UNIT 3 BIOLOGICAL DIVERSITY
Structure
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
3.12
3.13
Introduction
Objectives
Biological Diversity
3.3.1 Concept and Levels of Biological Diversity
3.3.2 Measurement of Biodiversity
3.3.3 The Current Status of Biodiversity
3.3.4 Distribution of Biodiversity
3.3.5 Evolution of Biodiversity
3.3.6 Role of Biodiversity in Ecosystem Function and Stability
Speciation
3.4.1 Concept of Species
3.4.2 Speciation : Natural Selection and Genetic Drift
3.4.3 Isolating Mechanisms
3.4.4 Natural Speciation
3.4.5 Genetic Drift
Extinction
3.5.1 Definition
3.5.2 Pseudoextinction
3.5.3 Causes of Extinction
IUCN Categories of Threat
3.6.1 2006 Release
3.6.2 2007 Release
3.6.3 Categories
3.6.4 Criticism
3.6.5 Mass Extinctions
Terrestrial Biodiversity
Biodiversity Hotspots
3.8.1 The Biodiversity Hotspots by Region
3.8.2 Approaches to Biodiversity Conservation
Biodiversity and Climate Change
Let us sum up
Check your progress and the key
Assignments/ Activities
References/ Further Readings
3.1
INTRODUCTION
Biodiversity is the variation of life forms within a given ecosystem, biome or for the
entire Earth. Biodiversity is often used as a measure of the health of biological systems.
Biodiversity found on earth today consists of many millions of distinct biological
species,. The whole of the earth's biodiversity - including all organisms and their
immense genetic variation, as well as their complex assemblages of communities and
ecosystems, is the result of four billion years of evolutionary change. Humanity shares
with all other species, a genetic heritage and numerous ecological linkages that form the
matrix, within which human societies have developed a complex set of psychological,
ethical and spiritual values, associated with biodiversity.
In this unit, we shall review all aspect of biological diversity in the world in general, and
India in particular. The diversity of species on earth constitutes a natural heritage and
life-support system for every country and all people. Humans have always depended on
the biodiversity around them for food, fuel, shelter, and health. The 80% world's
population relies on traditional medicines derived from natural bio-resources. Wild foods
still account over 40 percent of consumption by ethnic communities and others. The life giving services that are often taken for granted, maintenance of potable water, clean air,
and fertile soil all flow from the every day functions.and activities of healthy ecosystems.
Without biodiversity human would perish.
3.2
OBJECTIVES
The main objectives of this unit are to analyse the biological wealth present on the earth,
sustainable use of its components and their conservation. The major objectives of present
study are :
3.3

To understand the biological diversity and its component;

To study the importance of biological diversity in functioning and stability of
ecosystem;

To understand the importance of biological diversity for evolution and for
maintaining life sustaining systems of the biosphere,

To study the conservation and sustainable use of terrestrial biological diversity,

To study speciation, extinction and IUCN categories of threat.
BIOLOGICAL DIVERSITY
3.3.1 Concept and Levels of Biological Diversity
2
The term biological diversity defined as "variation of life at all levels of biological
organization". Another definition holds that biodiversity is a measure of the relative
diversity among organisms present in different ecosystems. "Diversity" in this definition
includes diversity within a species and among species, and comparative diversity among
ecosystems.
A third definition that is often used by ecologists is the "totality of genes, species, and
ecosystems of a region". An advantage of this definition is that it seems to describe most
circumstances and present a unified view of the traditional three levels at which
biodiversity has been identified:

Genetic diversity - diversity of genes within a species. There is a genetic variability
among the populations and the individuals of the same species.

Species diversity - diversity among species in an ecosystem. "Biodiversity hotspots"
are excellent examples of species diversity.

Ecosystem diversity - diversity at a higher level of organization, the ecosystem.
Diversity of habitat in a given unit area. To do with the variety of ecosystems on
Earth.
The 1992 United Nations Earth Summit in Rio de Janeiro defined "biodiversity" as "the
variability among living organisms from all sources, including, 'inter alia', terrestrial,
marine, and other aquatic ecosystems, and the ecological complexes of which they are
part: this includes diversity within species, between species and of ecosystems". This is,
in fact, the closest thing to a single legally accepted definition of biodiversity, since it is
the definition adopted by the United Nations Convention on Biological Diversity.
If the gene is the fundamental unit of natural selection, according to E. O. Wilson, the
real biodiversity is genetic diversity. For geneticists, biodiversity is the diversity of genes
and organisms. They study processes such as mutations, gene exchanges, and genome
dynamics that occur at the DNA level and generate evolution.
For ecologists, biodiversity is also the diversity of durable interactions among species. It
not only applies to species, but also to their immediate environment (biotope) and their
larger ecoregion. In each ecosystem, living organisms are part of a whole, interacting
with not only other organisms, but also with the air, water, and soil that surround them..
3.3.2 Measurement of Biodiversity
Biodiversity is a broad concept, so a variety of objective measures have been created in
order to empirically measure biodiversity. Each measure of biodiversity relates to a
particular use of the data.
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Biodiversity is usually plotted as taxonomic richness of a geographic area, with some
reference to a temporal scale. Whittaker described three common metrics used to measure
species-level biodiversity, encompassing attention to species richness or species
evenness:
Species richness - The least sophisticated indices of measurements of species diveristy.
There are two main indices are avialable :
1. Simpson's index (D) : Simpson (1949) gave the probability of any two individuals
drawn at random from an infinitely large community belonging to the same species as
:
D = P i2
Where, Pi = the proportion of individuals in the ith species.
2. Shannon-Weaver Index (Shannon and Weaver, 1949) : Shannon index takes into
account the degree of evenness in species abundances. The value of the Shannon
index obtained from empirical data usually falls between 1.5 and 3.5 and rarely
surpasses 4 (Margalef, 1972). The Shannon Index is calculated from the equation:
 ni   ni 
Shannan-Weaver Index (H') =     ln  
N N
Where;
ni
N
=
=
Number of individual species
Total number of species
There are three other indices which are commonly used by ecologists:

Alpha (α) diversity refers to diversity within a particular area, community or
ecosystem, and is measured by counting the number of taxa within the ecosystem
(usually species)

Beta (β) diversity is species diversity between ecosystems; this involves comparing
the number of taxa that are unique to each of the ecosystems.

Gamma (γ) diversity is a measure of the overall diversity for different ecosystems
within a region.
The relationship is as follows :
γ=α+β+Q
where, Q = Total number of habitats or communities,
α = Average value of α diversities,
β = Average value of β diversities.
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3.3.3 The Current Status of Biodiversity
Nobody knows for sure exactly how many species exist, or how rapidly species are
disappearing through extinction. About 1.75 million species out of an estimated total of
10-20 m. have been collected and named by systematizes, with the most undercounted
species being found among bacteria, protoctista (microorganisms), insects and fungi.
Though the total number of species is unknown, biologists and taxonomists have
accomplished reasonably complete samples in specific regions such as Western Europe.
Species inventories show that some ecosystems are richer in terms of biodiversity than
others. Groombridge and Jenkins (2000) go so far as to say, "The single most important
fact about biological diversity is that it is not evenly distributed over the planet."
As a soft guide, however, the numbers of identified species as of 2007 can be broken
down as follows:
1.
287,655 plants, including:
o
15,000 mosses,
o
13,025 ferns,
o
980 gymnosperms,
o
199,350 dicotyledons,
o
59,300 monocotyledons;
2.
74,000-120,000 fungi;
3.
10,000 lichens;
4.
1,250,000 animals, including:
o
o
1,190,200 invertebrates:

950,000 insects,

70,000 mollusks,

40,000 crustaceans,

130,200 others;
58,808 vertebrates:

29,300 fish,

5,743 amphibians,

8,240 reptiles,

10,234 birds, (9799 extant as of 2006)

5,416 mammals.
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Insects make up the vast majority of animal species. However the total number of species
for some phyla may be much higher:
5.
10-30 million insects;
6.
5-10 million bacteria;
7.
1.5 million fungi;
8.
~1 million mites
3.3.4 Distribution of Biodiversity
Biodiversity is not distributed uniformly across the globe. It is consistently richer in the
tropics and in other localized regions such as the California Floristic Province. As one
approaches Polar Regions one generally finds fewer species. Flora and fauna diversity
depends on climate, altitude, soils and the presence of other species. Generally, species
diversity per unit area tends to increase with decreasing latitude, with highest diversity
found in the tropics. Thus, in terms of natural land cover classes, tropical forests have the
highest densities of biodiversity per unit area; desert, tundra, and boreal forests have the
lowest. Topographical variations in the landscape lead to higher species diversity, and
some highly localized ecosystems, such as wetlands, are also species-rich. Recognition
that some areas possess higher levels of biodiversity, and especially endemics (plants or
animals that are only found in localized areas), has fueled interest in the identification of
biogeographical areas of species richness, and therefore of high conservation value.
Earth is endowed with immensely rich varieties of forms, which are roughly estimated as
20 million. Of these estimated species only 8% (i.e. 1.75 million) have been identified.
Amongst 1.75 million identified described organisms, producers constitute fairly
negligible proportion (4%), decomposers 15% and consumers 81%. When comparing this
proportion to the biomass generated by the three groups of organisms, the significance of
the group of producers becomes readily apparent, as they show highest biomass i.e.
(90%).
In our country, out of total identified species (microorganisms, plants, and animals),
producers, consumers, and decomposers constitute 19.6%, 58.4% and 22.0%,
respectively. The country is also rich in endemic species. The endemic plants comprise of
4950 angiosperms and 200 pteridophytes. The endemic animal species comprise of 37
mammal, 50 birds, 152 reptiles, 85 amphibians, 78 fishes and 635 invertebrates.
In the year 2006 large numbers of the Earth's species were formally classified as rare or
endangered or threatened species; moreover, many scientists have estimated that there are
millions more species actually endangered which have not yet been formally recognized.
About 40 percent of the 40,177 species assessed using the IUCN Red List criteria, are
now listed as threatened species with extinction - a total of 16,119 species.
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3.3.5 Evolution of Biodiversity
Biodiversity found on Earth today is the result of 4 billion years of evolution. The origin
of life has not been definitely established by science, however some evidence suggests
that life may already have been well-established a few hundred million years after the
formation of the Earth. Until approximately 600 million years ago, all life consisted of
bacteria and similar single-celled organisms.
The history of biodiversity during the Phanerozoic (the last 540 million years), starts with
rapid growth during the Cambrian explosion—a period during which nearly every
phylum of multicellular organisms first appeared. Over the next 400 million years or so,
global diversity showed little overall trend, but was marked by periodic, massive losses
of diversity classified as mass extinction events.
Fig. 3.1 : Apparent marine fossil diversity during the Phanerozoic
The apparent biodiversity shown in the fossil record (Fig. 3.1) suggests that the last few
million years include the period of greatest biodiversity in the Earth's history. However,
not all scientists support this view, since there is considerable uncertainty as to how
strongly the fossil record is biased by the greater availability and preservation of recent
geologic sections. Some scientists argue that corrected for sampling artifacts, modern
biodiversity is not much different from biodiversity 300 million years ago. Estimates of
the present global macroscopic species diversity vary from 2 million to 100 million
species, with a best estimate of somewhere near 13-14 million, the vast majority of them
arthropods.
Most biologists agree however that the period since the emergence of humans is part of a
new mass extinction, the Holocene extinction event, caused primarily by the impact
humans are having on the environment. It has been argued that the present rate of
extinction is sufficient to eliminate most species on the planet Earth within 100 years.
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New species are regularly discovered (on average between 5-10,000 new species each
year, most of them insects) and many, though discovered, are not yet classified (estimates
are that nearly 90% of all arthropods are not yet classified). Most of the terrestrial
diversity is found in tropical forests.
3.3.6 Role of Biodiversity in Ecosystem Function and Stability
There are a multitude of anthropocentric benefits of biodiversity in ecosystem function
and stability. Biodiversity is central to an ecocentric philosophy. It is important to
understand the reasons for believing in conservation of biodiversity. One way to identify
the reasons why we believe in it is to look at what we get from biological diversity and
the things that we loose as a result of species extinction, which has taken place over the
last 600 years. Mass extinction is the direct result of human activity and not of natural
phenomena which is the perception of many modern day thinkers.
Biodiversity provides many ecosystem services that are often not readily visible. It plays
a part in regulating the chemistry of our atmosphere and water supply. Biodiversity is
directly involved in recycling nutrients and providing fertile soils. Experiments with
controlled environments have shown that humans cannot easily build ecosystems to
support human needs; for example insect pollination cannot be mimicked by humanmade construction, and that activity alone represents tens of billions of dollars in
ecosystem services per annum to humankind.
There are many benefits that are obtained from natural ecosystem processes. Some
ecosystem services that benefit to society are air quality, climate (both global CO2
sequestration and regional and local), water purification, disease control, biological pest
control, pollination and prevention of erosion. Along with those come non- material
benefits that are obtained from ecosystems which are spiritual and aesthetic values,
knowledge systems and the value of education that we obtain today. However, the public
remains unaware of the crisis in sustaining biodiversity. Biodiversity takes a look into the
importance to life and provides modern audiences with a clear understanding of the
current threat to life on Earth.
In Agriculture
For some foodcrops and other economic crops, wild varieties of the domesticated species
can be reintroduced to form a better variety than the previous (domesticated) species. The
economic impact is gigantic, for even crops as common as the potato (which was bred
through only one variety, brought back from the Inca), a lot more can come from these
species. Wild varieties of the potato will all suffer enormously through the effects of
climate change. A report by the Consultative Group on International Agricultural
Research (CGIAR) describes the huge economic loss. Rice, which has been improved for
thousands of years by humans, can through the same process regain some of its
nutritional value that has been lost since.
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Crop diversity is also necessary to help the system recover when the dominant crop type
is attacked by a disease:
1. The Irish potato blight of 1846, which was a major factor in the deaths of a million
people and migration of another million, was the result of planting only two potato
varieties, both of which were vulnerable.
2. When the rice grassy stunt virus struck rice fields from Indonesia to India in the
1970s, 6273 varieties were tested. Only one was luckily found to be resistant, a
relatively feeble Indian variety, known to science only since 1966, with the desired
trait. It was hybridised with other varieties and now widely grown.
3. In 1970, coffee rust attacked coffee plantations in Sri Lanka, Brazil, and Central
America. A resistant variety was found in Ethiopia, coffee's presumed homeland,
which mitigated the rust epidemic.
Monoculture, the lack of biodiversity, was a contributing factor to several agricultural
disasters in history, including the Irish Potato Famine, the European wine industry
collapse in the late 1800s, and the US Southern Corn Leaf Blight epidemic of 1970.
Higher biodiversity also controls the spread of certain diseases as pathogens will need
adapt to infect different species.
Biodiversity provides food for humans. Although about 80 percent of our food supply
comes from just 20 kinds of plants, humans use at least 40,000 species of plants and
animals a day. Many people around the world depend on these species for their food,
shelter, and clothing. There is untapped potential for increasing the range of food
products suitable for human consumption, provided that the high present extinction rate
can be stopped.
Science and medicine
A significant proportion of drugs are derived, directly or indirectly, from biological
sources; in most cases these medicines can not presently be synthesized in a laboratory
setting. About 40% of the pharmaceuticals using natural compounds found in plants,
animals, and microorganisms. Moreover, only a small proportion of the total diversity of
plants has been thoroughly investigated for potential sources of new drugs. Many drugs
are also derived from microorganisms.
Through the field of bionics, considerable technological advancement has occurred which
would not have without a rich biodiversity. ..
Industrial materials
A wide range of industrial materials are derived directly from biological resources. These
include building materials, fibers, dyes, resins, gums, adhesives, rubber and oil. There is
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enormous potential for further research into sustainably utilizing materials from a wider
diversity of organisms.
Leisure, cultural and aesthetic value
Many people derive value from biodiversity through leisure activities such as hiking in
the countryside, birdwatching or natural history study. Biodiversity has inspired
musicians, painters, sculptors, writers and other artists. Many cultural groups view
themselves as an integral part of the natural world and show respect for other living
organisms.
Popular activities such as gardening, caring for aquariums and collecting butterflies are
all strongly dependent on biodiversity. The number of species involved in such pursuits is
in the tens of thousands, though the great majority do not enter mainstream
commercialism.
The relationships between the original natural areas of these often 'exotic' animals and
plants and commercial collectors, suppliers, breeders, propagators and those who
promote their understanding and enjoyment are complex and poorly understood. It seems
clear, however, that the general public responds well to exposure to rare and unusual
organisms-- they recognize their inherent value at some level, even if they would not
want the responsibility of caring for them. A family outing to the botanical garden or zoo
is as much an aesthetic or cultural experience as it is an educational one.
Philosophically it could be argued that biodiversity has intrinsic aesthetic and/ or spiritual
value to mankind in and of itself. This idea can be used as a counterweight to the rather
notion that tropical forests and other ecological realms are only worthy of conservation
because they may contain medicines or useful products.
3.4
SPECIATION
Speciation is the process by which new species of organisms arise. Earth is inhabited by
millions of different organisms, all of which likely arose from one early life-form that
came into existence about 3.5 billion years ago. It is the task of taxonomists to decide
which out of the multitude of different types of organisms should be considered species.
The wide range in the characteristics of individuals within groups makes defining a
species more difficult. Indeed, the definition of species itself is open to debate.
3.4.1 Concepts of Species
In the broadest sense, a species can be defined as a group of individuals that is "distinct"
from another group of individuals. Several different views have been put forward about
what constitutes an appropriate level of difference. Principal among these views are the
biological-species concept and the morphological-species concept.
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The biological-species concept delimits species based on breeding. Members of a single
species are those that interbreed to produce fertile offspring or have the potential to do so.
The morphological-species concept (from the ancient Greek root "morphos," meaning
form) is based on classifying species by a difference in their form or function. According
to this concept, members of the same species share similar characteristics. Species that
are designated by this criterion are known as a morphological species.
Organisms within a species do not necessarily look identical. For example, the domestic
dog is considered to be one species, even though there is a huge range in size and
appearance among the different breeds. For naturally occurring populations of organisms
that we are much less familiar with, it is much more difficult to recognize the significance
of any character differences observed. Therefore deciding what characteristics should be
used, as criteria to designate a species can be difficult.
3.4.2 Speciation : Natural Selection and Genetic Drift
Before the development of the modern theory of evolution, a widely held idea regarding
the diversity of life was the "typological" or "essentialist" view. This view held that a
species at its core had an unchanging perfect "type" and that any variations on this perfect
type were imperfections due to environmental conditions. Charles Darwin (1809-1882)
and Alfred Russel Wallace (1823-1913) independently developed the theory of evolution
by natural selection, now commonly known as Darwinian evolution.
The theory of Darwinian evolution is based on two main ideas. The first is that heritable
traits that confer an advantage to the individual that carries them will become more
widespread in a population through natural selection because organisms with these
favorable traits will produce more offspring. Since different environments favor different
traits, Darwin saw that the process of natural selection would, over time, make two
originally similar groups become different from one another, ultimately creating two
species from one. This led to the second major idea, which is that all species arise from
earlier species, therefore sharing a common ancestor.
When so much change occurs between different groups that they are morphologically
distinct or no longer able to interbreed, they may be considered different species; this
process is known as speciation. A species as a whole can transform over time into a new
species (vertical evolution) or split into more separate populations, each of which may
develop into new species (adaptive radiation).
Modern population geneticists recognize that natural selection is not the only factor
causing genetic change in a population over time. Genetic drift is the random change in
the genetic composition of a small population over time, due to an unequal genetic
contribution by individuals to succeeding generations. It is thought that genetic drift can
result in new species, especially in small isolated populations.
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3.4.3 Isolating Mechanisms
Whether natural selection and genetic drift lead to new species depends on whether there
is restricted gene flow between different groups. Gene flow is the movement of genes
between separate populations by migration of individuals. If two populations remain in
contact, gene flow will prevent them from becoming separate species (though they may
both develop into a new species through vertical evolution).
Gene flow is restricted through geographic effects such as mountain ranges and oceans,
leading to geographic isolation. Gene flow can also be prevented by biological factors
known as isolating mechanisms. Biological isolating mechanisms include differences in
behavior (especially mating behavior), and differences in habitat use, both of which lead
to a decrease in mating between individuals from different groups.
When geographic separation plays a role in speciation, this is known as allopatric
speciation, from the Greek roots allo, meaning separate, and "patric," meaning country.
In allopatric speciation, natural selection and genetic drift can act together.
For example, imagine a mudslide that causes a river to back up into a valley, separating a
population of rodents into two, one restricted to the shady side of the river, the other to
the sunny side. Because coat thickness is a genetically inherited trait, eventually, through
natural selection, the population of animals on the cooler side may develop thicker coats.
After many generations of separation, the two groups may look quite different and may
have evolved different behaviors as well, to allow them to survive better in their
respective habitats. Genetic drift may occur especially if either or both populations
remain small. Eventually these two populations may be so different as to warrant
designation as different species.
It is also possible for new species to form from a single population without any
geographic separation. This is known as "ecological" or "sympatric" (from the Greek root
sym, meaning same) speciation, and it results in ecological differences between
morphologically similar species inhabiting the same area. Sympatric speciation can occur
in flowering plants in a single generation, due to the formation of a polyploid. Polyploidy
is the complete duplication of an organism's genome, for example from n chromosomes
to 4n. Even higher multiples of n are possible. This increase in a plant's DNA content
makes it reproductively incompatible with other individuals of its former species.
Formation of new and distinct species, whereby a single evolutionary line splits into two
or more genetically independent ones. One of the fundamental processes of evolution,
speciation may occur in many ways. Investigators formerly found evidence for speciation
in the fossil record by tracing sequential changes in the structure and form of organisms.
Genetic studies now show that such changes do not always accompany speciation, since
many apparently identical groups are in fact reproductively isolated (i.e., they can no
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longer produce viable offspring through interbreeding). Polyploidy is a means by which
the beginnings of new species are created in just two or three generations.
Speciation is the evolutionary process by which new biological species arise. There are
four modes of natural speciation, based on the extent to which speciating populations are
geographically isolated from one another: allopatric, peripatric, parapatric and sympatric.
Speciation may also be induced artificially, through animal husbandry or laboratory
experiments. Observed examples of each kind of speciation are provided throughout.
3.4.4 Natural speciation
All forms of natural speciation have taken place over the course of evolution, though it
still remains a subject of debate as to the relative importance of each mechanism in
driving biodiversity.
There is debate as to the rate at which speciation events occur over geologic time. While
some evolutionary biologists claim that speciation events have remained relatively
constant over time, some paleontologists such as Niles Eldredge and Stephen Jay Gould
have argued that species usually remain unchanged over long stretches of time, and that
speciation occurs only over relatively brief intervals, a view known as punctuated
equilibrium.
Allopatric (geographic)
During allopatric speciation, a population splits into two geographically isolated
allopatric populations (for example, by habitat fragmentation due to geographical change
such as mountain building or social change such as emigration). The isolated populations
then undergo genotypic and/or phenotypic divergence as they (a) become subjected to
dissimilar selective pressures or (b) they independently undergo genetic drift. When the
populations come back into contact, they have evolved such that they are reproductively
isolated and are no longer capable of exchanging genes.
Observed instances : Island genetics, the tendency of small, isolated genetic pools to
produce unusual traits, has been observed in many circumstances, including insular
dwarfism and the radical changes among certain famous island chains, like Komodo and
Galapagos, the latter having given rise to the modern expression of evolutionary theory,
after being observed by Charles Darwin. Perhaps the most famous example of allopatric
speciation is Darwin's Galápagos Finches.
Peripatric (Mostly geographic)
In peripatric speciation, new species are formed in isolated, small peripheral populations,
which are prevented from exchanging genes with the main population. It is related to the
13
concept of a founder effect, since small populations often undergo bottlenecks. Genetic
drift is often proposed to play a significant role in peripatric speciation. E.g.

Mayr bird fauna

The Australian bird Petroica multicolor

Reproductive isolation occurs in populations of Drosophila subject to population
bottlenecking
Parapatric (Somewhat geographic)
In parapatric speciation, the zones of two diverging populations are separate but do
overlap. There is only partial separation afforded by geography, so individuals of each
species may come in contact or cross the barrier from time to time, but reduced fitness of
the heterzygote leads to selection for behaviours or mechanisms which prevent breeding
between the two species.
Ecologists refer to parapatric and peripatric speciation in terms of ecological niches. A
niche must be available in order for a new species to be successful.
Observed instances

Ring species

The Larus gulls form a ring species around the North Pole.

The Ensatina salamanders, which form a ring round the Central Valley in California.

The Greenish Warbler (Phylloscopus trochiloides), around the Himalayas.

the grass Anthoxanthum has been known to undergo parapatric speciation in such
cases as mine contamination of an area.
Sympatric (Non-geographic)
In sympatric speciation, species diverge while inhabiting the same place. Examples of
sympatric speciation are found in insects which become dependent on different host
plants in the same area.
Speciation via polyploidy: A diploid cell undergoes failed meiosis, producing diploid
gametes, which self-fertilize to produce a tetraploid zygote.
Polyploidy is a mechanism often attributed to causing some speciation events in
symparty. Not all polyploids are reproductively isolated from their parental plants, so an
increase in chromosome number may not result in the complete cessation of gene flow
between the incipient polyploids and their parental diploids.
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Polyploidy is observed in many species of both plant and animal like wheat, Salsify or
goatsbeard, Cichlids of Lake Victoria, Lake Tanganyika and Lake Malawi, Xenopus
laevis, and an African frog.
Hybridization between two different species sometimes leads to a distinct phenotype.
This phenotype can also be fitter than the parental lineage and as such natural selection
may then favor these individuals. Eventually, if reproductive isolation is achieved, it may
lead to a separate species. However, reproductive isolation between hybrids and their
parents is particularly difficult to achieve and thus hybrid speciation is considered an
extremely rare event.
Fig 3.2 Comparison of Allopatric, Peripatric, Parapatric and Sympatric Speciation.
Reinforcement
Reinforcement is the process by which natural selection increases reproductive isolation.
It may occur after two populations of the same species are separated and then come back
into contact. If their reproductive isolation was complete, then they will have already
developed into two separate incompatible species. If their reproductive isolation is
incomplete, then further mating between the populations will produce hybrids, which
may or may not be fertile. If the hybrids are infertile, or fertile but less fit than their
ancestors, then there will be no further reproductive isolation and speciation has
essentially occurred (e.g., as in horses and donkeys.) If the hybrid offspring are more fit
than their ancestors, then the populations will merge back into the same species within
the area they are in contact.
Reinforcement is required for both parapatric and sympatric speciation. Without
reinforcement, the geographic area of contact between different forms of the same
15
species, called their "hybrid zone," will not develop into a boundary between the different
species. And also without reinforcement they will have uncontrollable interbreeding.
Reinforcement may be induced in artificial selection experiments as described below.
Artificial speciation
New species have been created by domesticated animal husbandry, but the initial dates
and methods of the initiation of such species are not clear. For example, domestic sheep
were created by hybridisation, and no longer produce viable offspring with Ovis
orientalis, one species from which they are descended. Domestic cattle, on the other
hand, can be considered the same species as several varieties of wild ox, gaur, yak, etc.,
as they readily produce fertile offspring with them.
The best-documented creations of new species in the laboratory were performed in the
late 1980s. William Rice and G.W. Salt bred fruit flies, Drosophila melanogaster, using a
maze with three different choices such as light/dark and wet/dry. Each generation was
placed into the maze, and the groups of flies which came out of two of the eight exits
were set apart to breed with each other in their respective groups. After thirty-five
generations, the two groups and their offspring would not breed with each other even
when doing so was their only opportunity to reproduce.
Diane Dodd was also able to show allopatric speciation by reproductive isolation in
Drosophila pseudoobscura fruit flies after only eight generations using different food
types, starch and maltose. Dodd's experiment has been easy for many others to replicate,
including with other kinds of fruit flies and foods (Fig 3.3). The history of such attempts
is described in Rice and Hostert (1993).
Fig: 3.3 The Drosophila experiment conducted by Diane Dodd in 1989.
16
3.4.5 Genetics Drift
Hybrid speciation
Hybridization between two different species sometimes leads to a distinct phenotype.
This phenotype can also be fitter than the parental lineage and as such natural selection
may then favor these individuals. Eventually, if reproductive isolation is achieved, it may
lead to a separate species. However, reproductive isolation between hybrids and their
parents is particularly difficult to achieve and thus hybrid speciation is considered an
extremely rare event. The Mariana Mallard arose from hybrid speciation.
Hybridization without change in chromosome number is called homoploid hybrid
speciation. It is considered very rare but has been shown in Heloconius butterflies and
sunflowers. Polyploid speciation, which involves changes in chromosome number, is a
more common phenomenon, especially in plant species.
Gene transposition as a cause
Theodosius Dobzhansky, who studied fruit flies in the early days of genetic research in
1930s, speculated that parts of chromosomes that switch from one location to another
might cause a species to split into two different species. He mapped out how it might be
possible for sections of chromosomes to relocate themselves in a genome. Those mobile
sections can cause sterility in inter-species hybrids, which can act as a speciation
pressure. In theory, his idea was sound, but scientists long debated whether it actually
happened in nature. Eventually a competing theory involving the gradual accumulation of
mutations was shown to occur in nature so often that geneticists largely dismissed the
moving gene hypothesis.
However, recent research shows that jumping of a gene from one chromosome to another
can contribute to the birth of new species. This validates the reproductive isolation
mechanism, a key component of speciation.
Interspersed repeats
Interspersed repetitive DNA sequences function as isolating mechanisms. These repeats
protect newly evolving gene sequences from being overwritten by gene conversion, due
to the creation of non-homologies between otherwise homologous DNA sequences. The
non-homologies create barriers to gene conversion. This barrier allows nascent novel
genes to evolve without being overwritten by the progenitors of these genes. This
uncoupling allows the evolution of new genes, both within gene families and also allelic
forms of a gene. The importance is that this allows the splitting of a gene pool without
requiring physical isolation of the organisms harboring those gene sequences.
Human speciation
17
Humans have genetic similarities with chimpanzees and gorillas, suggesting common
ancestors. Analysis of genetic drift and recombination suggests humans and chimpanzees
speciated apart 4.1 million years ago.
3.5
EXTINCTION
In biology and ecology, extinction is the cessation of existence of a species or group of
taxa. The moment of extinction is generally considered to be the death of the last
individual of that species (although the capacity to breed and recover may have been lost
before this point). Because a species' potential range may be very large, determining this
moment is difficult, and is usually done retrospectively. This difficulty leads to
phenomena such as Lazarus taxa, where a species presumed extinct abruptly "re-appears"
(typically in the fossil record) after a period of apparent absence.
Through evolution, new species arise through the process of speciation — where new
varieties of organisms arise and thrive when they are able to find and exploit an
ecological niche — and species become extinct when they are no longer able to survive
in changing conditions or against superior competition. A typical species becomes extinct
within 10 million years of its first appearance, although some species, called living
fossils, survive virtually unchanged for hundreds of millions of years. Extinction, though,
is usually a natural phenomenon; it is estimated that 99.9% of all species that have ever
lived are now extinct.
Prior to the dispersion of humans across the earth, extinction generally occurred at a
continuous low rate, mass extinctions being relatively rare events. Starting approximately
100,000 years ago, and coinciding with an increase in the numbers and range of humans,
species extinctions have increased to a rate unprecedented since the Cretaceous–Tertiary
extinction event. This is known as the Holocene extinction event and is at least the sixth
such extinction event. Some experts have estimated that up to half of presently existing
species may become extinct by 2100.
3.5.1 Definition
A species becomes extinct when the last existing member of that species dies. Extinction
therefore becomes a certainty when there are no surviving individuals that are able to
reproduce and create a new generation. A species may become functionally extinct when
only a handful of individuals survive, which are unable to reproduce due to poor health,
age, sparse distribution over a large range, a lack of individuals of both sexes (in sexually
reproducing species), or other reasons.
Bark from the extinct Lepidodendron, which died out after the Carboniferous, likely due
to competition from newer plant life.
18
Pinpointing the extinction (or pseudoextinction) of a species requires a clear definition of
that species. If it is to be declared extinct, the species in question must be uniquely
identifiable from any ancestor or daughter species, or from other closely related species.
Extinction of a species (or replacement by a daughter species) plays a key role in the
punctuated equilibrium hypothesis of Stephen Jay Gould and Niles Eldredge.
In ecology, extinction is often used informally to refer to local extinction, in which a
species ceases to exist in the chosen area of study, but still exists elsewhere. This
phenomenon is also known as extirpation. Local extinctions may be followed by a
replacement of the species taken from other locations; wolf reintroduction is an example
of this. Species which are not extinct are termed extant. Those that are extant but
threatened by extinction are referred to as threatened or endangered species.
An important aspect of extinction at the present time are human attempts to preserve
critically endangered species, which is reflected by the creation of the conservation status
"Extinct in the Wild" (EW). Species listed under this status by the World Conservation
Union (IUCN) are not known to have any living specimens in the wild, and are
maintained only in zoos or other artificial environments. Some of these species are
functionally extinct, as they are no longer part of their natural habitat and it is unlikely
the species will ever be restored to the wild. When possible, modern zoological
institutions attempt to maintain a viable population for species preservation and possible
future reintroduction to the wild through use of carefully planned breeding programs.
The extinction of one species' wild population can have knock-on effects, causing further
extinctions. These are also called "chains of extinction".
3.5.2 Pseudoextinction
Descendants may or may not exist for extinct species. Daughter species that evolve from
a parent species carry on most of the parent species' genetic information, and even though
the parent species may become extinct, the daughter species lives on. In other cases,
species have produced no new variants, or none that are able to survive the parent species'
extinction. Extinction of a parent species where daughter species or subspecies are still
alive is also called pseudoextinction.
Pseudoextinction is difficult to demonstrate unless one has a strong chain of evidence
linking a living species to members of a pre-existing species. For example, it is
sometimes claimed that the extinct Hyracotherium, which was an ancient animal similar
to the horse, is pseudoextinct, rather than extinct, because there are several extant species
of equus, including zebra and donkeys. However, as fossil species typically leave no
genetic material behind, it is not possible to say whether Hyracotherium actually evolved
into more modern horse species or simply evolved from a common ancestor with modern
horses. Pseudoextinction is much easier to demonstrate for larger taxonomic groups. It is
19
said that dinosaurs are pseudoextinct, because some of their descendants, the birds,
survive today.
3.5.3 Causes of Extinction


The passenger pigeon, one of several species of extinct birds, was hunted to
extinction over the course of a few decades.
The Bali Tiger was declared extinct in 1937 due to hunting and habitat loss.
There are a variety of causes that can contribute directly or indirectly to the extinction of
a species or group of species. "Just as each species is unique," write Beverly and Stephen
Stearns, "so is each extinction... the causes for each are varied — some subtle and
complex, others obvious and simple". Most simply, any species that is unable to survive
or reproduce in its environment, and unable to move to a new environment where it can
do so, dies out and becomes extinct. Extinction of a species may come suddenly when an
otherwise healthy species is wiped out completely, as when toxic pollution renders its
entire habitat unlivable; or may occur gradually over thousands or millions of years, such
as when a species gradually loses out in competition for food to better adapted
competitors.
Assessing the relative importance of genetic factors compared to environmental ones as
the causes of extinction has been compared to the nature-nurture debate. The question of
whether more extinctions in the fossil record have been caused by evolution or by
catastrophe is a subject of discussion; Mark Newman, the author of Modeling Extinction
argues for a mathematical model that falls between the two positions. By contrast,
conservation biology uses the extinction vortex model to classify extinctions by cause.
When concerns about human extinction have been raised, for example in Sir Martin Rees'
2003 book Our Final Hour, those concerns lie with the effects of climate change or
technological disaster.
Currently, environmental groups and some governments are concerned with the
extinction of species caused by humanity, and are attempting to combat further
extinctions through a variety of conservation programs. Humans can cause extinction of a
species through overharvesting, pollution, habitat destruction, introduction of new
predators and food competitors, overhunting, and other influences. According to the
World Conservation Union (WCU, also known as IUCN), 784 extinctions have been
recorded since the year 1500, the arbitrary date selected to define "modern" extinctions,
with many more likely to have gone unnoticed.
Genetics and demographic phenomena
Population genetics and demographic phenomena affect the evolution, and therefore the
risk of extinction, of species. Species with small populations are much more vulnerable to
these types of effects. Limited geographic range is the most important determinant of
20
genus extinction at background rates but becomes increasingly irrelevant as mass
extinction arises.
Natural selection acts to propagate beneficial genetic traits and eliminate weaknesses. It
is nevertheless possible for a deleterious mutation to be spread throughout a population
through the effect of genetic drift.
A diverse or "deep" gene pool gives a population a higher chance of surviving an adverse
change in conditions. Effects that cause or reward a loss in genetic diversity can increase
the chances of extinction of a species. Population bottlenecks can dramatically reduce
genetic diversity by severely limiting the number of reproducing individuals and make
inbreeding more frequent. The founder effect can cause rapid, individual-based speciation
and is the most dramatic example of a population bottleneck.
Genetic pollution : Purebred naturally evolved region specific wild species can be
threatened with extinction in a big way through the process of Genetic Pollution i.e.
uncontrolled hybridization, introgression and Genetic swaping which leads to
homogenization or replacement of local genotypes as a result of either a numerical and/or
fitness advantage of introduced plant or animal. Nonnative species can bring about a form
of extinction of native plants and animals by hybridization and introgression either
through purposeful introduction by humans or through habitat modification, bringing
previously isolated species into contact. These phenomena can be especially detrimental
for rare species coming into contact with more abundant ones where the abundant ones
can interbreed with them swamping the entire rarer gene pool creating hybrids thus
driving the entire original purebred native stock to complete extinction. Such extinctions
are not always apparent from morphological (outward appearance) observations alone.
Some degree of gene flow may be a normal, evolutionarily constructive process, and all
constellations of genes and genotypes cannot be preserved however, hybridization with or
without introgression may, nevertheless, threaten a rare species' existence.
Widespread genetic pollution also leads to weakening of the naturally evolved (wild)
region specific gene pool leading to weaker hybrid animals and plants which are not able
to cope with natural environs over the long run and fast tracks them towards final
extinction.
The gene pool of a species or a population is the complete set of unique alleles that would
be found by inspecting the genetic material of every living member of that species or
population. A large gene pool indicates extensive genetic diversity, which is associated
with robust populations that can survive bouts of intense selection. Meanwhile, low
genetic diversity (see inbreeding and population bottlenecks) can cause reduced
biological fitness and an increased chance of extinction amongst the reducing population
of purebred individuals from a species.
21
Habitat degradation : The degradation of a species' habitat may alter the fitness
landscape to such an extent that the species is no longer able to survive and becomes
extinct. This may occur by direct effects, such as the environment becoming toxic, or
indirectly, by limiting a species' ability to compete effectively for diminished resources or
against new competitor species.
Habitat degradation through toxicity can kill off a species very rapidly, by killing all
living members through contamination or sterilizing them. It can also occur over longer
periods at lower toxicity levels by affecting life span, reproductive capacity, or
competitiveness.
Habitat degradation can also take the form of a physical destruction of niche habitats. The
widespread destruction of tropical rainforests and replacement with open pastureland is
widely cited as an example of this; elimination of the dense forest eliminated the
infrastructure needed by many species to survive. For example, a fern that depends on
dense shade for protection from direct sunlight can no longer survive without forest to
shelter it. Another example is the destruction of ocean floors by bottom trawling.
Diminished resources or introduction of new competitor species also often accompany
habitat degradation. Global warming has allowed some species to expand their range,
bringing unwelcome competition to other species that previously occupied that area.
Sometimes these new competitors are predators and directly affect prey species, while at
other times they may merely outcompete vulnerable species for limited resources. Vital
resources including water and food can also be limited during habitat degradation,
leading to extinction.
The Golden Toad was last seen on May 15, 1989. Decline in amphibian populations is
ongoing worldwide.
Predation, competition, and disease : Humans have been transporting animals and
plants from one part of the world to another for thousands of years, sometimes
deliberately (e.g., livestock released by sailors onto islands as a source of food) and
sometimes accidentally (e.g., rats escaping from boats). In most cases, such introductions
are unsuccessful, but when they do become established as an invasive alien species, the
consequences can be catastrophic. Invasive alien species can affect native species directly
by eating them, competing with them, and introducing pathogens or parasites that sicken
or kill them or, indirectly, by destroying or degrading their habitat. Human populations
may themselves act as invasive predators. According to the "overkill hypothesis", the
swift extinction of the megafauna in areas such as New Zealand, Australia, Madagascar
and Hawaii resulted from the sudden introduction of human beings to environments full
of animals that had never seen them before, and were therefore completely unadapted to
their predation techniques.
Coextinction
22
Coextinction refers to the loss of a species due to the extinction of another; for example,
the extinction of parasitic insects following the loss of their hosts. Coextinction can also
occur when a species loses its pollinator, or to predators in a food chain who lose their
prey. "Species coextinction is a manifestation of the interconnectedness of organisms in
complex ecosystems ... While coextinction may not be the most important cause of
species extinctions, it is certainly an insidious one".
3.6
IUCN CATEGORIES OF THREAT
The IUCN Red List of Threatened Species (also known as the IUCN Red List or Red
Data List), created in 1963, is the world's most comprehensive inventory of the global
conservation status of plant and animal species. The International Union for the
Conservation of Nature and Natural Resources (IUCN) is the world's main authority on
the conservation status of species.
The IUCN Red List is set upon precise criteria to evaluate the extinction risk of
thousands of species and subspecies. These criteria are relevant to all species and all
regions of the world. The aim is to convey the urgency of conservation issues to the
public and policy makers, as well as help the international community to try to reduce
species extinction.
Major species assessors include Bird Life International, the Institute of Zoology (the
research division of the Zoological Society of London), the World Conservation
Monitoring Center, and many Specialist Groups within the IUCN's Species Survival
Commission (SSC). Collectively, assessments by these organizations and groups account
for nearly half the species on the Red List.
IUCN Red List is widely considered to be the most objective and authoritative system for
classifying species in terms of the risk of extinction.
The IUCN aims to have the category of every species re-evaluated every 5 years if
possible, or at least every ten years. This is done in a peer-reviewed manner through
IUCN Species Survival Commission (SSC) Specialist Groups, which are Red List
Authorities responsible for a species, group of species or specific geographic area, or in
the case of Bird Life International, an entire class (Aves). There are over 7000 extant
species in the 2006 Red List which have not had their category evaluated since 1996.
The IUCN Red List Categories and Criteria have several specific aims:
 To provide a system that can be applied consistently by different people;
 To improve objectivity by providing users with clear guidance on how to evaluate
different factors which affect the risk of extinction;
 To provide a system which will facilitate comparisons across widely different taxa;
23
To give people using threatened species lists a better understanding of how individual
species were classified.
Fig. 3.4 : The percentage of species in several groups, which are listed as
Critical
endangered
or vulnerable
on the 2007 IUCN Red List.
3.6.1 2006 release
The 2006 Red List, released on 4 May 2006 evaluated 40,168 species as a whole, plus an
additional 2,160 subspecies, varieties, aquatic stocks, and subpopulations.
From the species evaluated as a whole, 16,118 were considered threatened. Of these,
7,725 were animals, 8,390 were plants, and three were lichen and mushrooms.
This release listed 784 species extinctions recorded since 1500 CE, unchanged from the
2004 release. This was an increase of 18 from the 766 listed as of 2000. Each year a
small number of "extinct" species may be rediscovered, becoming Lazarus species, or
may be reclassified as "data deficient". In 2002, the extinction list dropped to 759
species, but has been rising ever since.
3.6.2 2007 release
On September 12, 2007, the World Conservation Union (IUCN) released the 2007 IUCN
Red List of Threatened Species, the latest update to their online database of species'
extinction risks. In this release, they have raised their classification of both the Western
24
Lowland Gorilla (Gorilla gorilla gorilla) and the Cross River Gorilla (Gorilla gorilla
diehli) from Endangered to Critically Endangered, which is the last category before
Extinct in the Wild, due to Ebola virus and poaching, along with other factors. Russ
Mittermeier, chief of Swiss-based IUCN's Primate Specialist Group, stated that 16,306
species are endangered with extinction, 188 more than in 2006 (total of 41,415 species on
the Red List). The Red List includes the Sumatran Orangutan (Pongo abelii) in the
Critically Endangered category and the Bornean Orangutan (Pongo pygmaeus) in the
Endangered category.
3.6.3 Categories
Species are classified in nine groups, set through criteria such as rate of decline,
population size, area of geographic distribution, and degree of population and distribution
fragmentation. A representation of the relationships between the categories is shown in
Figure 3.5.
Fig. 3.5 : Structure of the categories of IUCN Red List
a. Extinct (EX) : A taxon is Extinct when there is no reasonable doubt that the last
individual has died. A taxon is presumed Extinct when exhaustive surveys in known
and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout
its historic range have failed to record an individual. Surveys should be over a time
frame appropriate to the taxon's life cycle and life form.
b. Extinct in the Wild (EW) : A taxon is Extinct in the Wild when it is known only
to survive in cultivation, in captivity or as a naturalized population (or populations)
well outside the past range. A taxon is presumed Extinct in the Wild when exhaustive
surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal,
25
annual), throughout its historic range have failed to record an individual. Surveys
should be over a time frame appropriate to the taxon's life cycle and life form.
c. Critically Endangered (CR) : A taxon is Critically Endangered when the best
available evidence indicates that it meets any of the criteria A to E for Critically
Endangered (see Section V), and it is therefore considered to be facing an extremely
high risk of extinction in the wild.
d. Endangered (EN) : A taxon is Endangered when the best available evidence
indicates that it meets any of the criteria A to E for Endangered (see Section
V), and it is therefore considered to be facing a very high risk of extinction in
the wild.
e. Vulnerable (VU) : A taxon is Vulnerable when the best available evidence
indicates that it meets any of the criteria A to E for Vulnerable (see Section V),
and it is therefore considered to be facing a high risk of extinction in the wild.
f. Near Threatened (NT) : A taxon is Near Threatened when it has been
evaluated against the criteria but does not qualify for Critically Endangered,
Endangered or Vulnerable now, but is close to qualifying for or is likely to
qualify for a threatened category in the near future.
g. Least Concern (LC) : A taxon is Least Concern when it has been evaluated
against the criteria and does not qualify for Critically Endangered, Endangered,
Vulnerable or Near Threatened. Widespread and abundant taxa are included in
this category.
In the 2001 system, Near Threatened and Least Concern have now become their own
categories, while Conservation Dependent is no longer used and has been merged into
Near Threatened.
h. Data Deficient (DD) : A taxon is Data Deficient when there is inadequate
information to make a direct, or indirect, assessment of its risk of extinction based on
its distribution and/or population status. A taxon in this category may be well studied,
and its biology well known, but appropriate data on abundance and/or distribution are
lacking. Data Deficient is therefore not a category of threat. Listing of taxa in this
category indicates that more information is required and acknowledges the possibility
that future research will show that threatened classification is appropriate. It is
important to make positive use of whatever data are available. In many cases great
care should be exercised in choosing between DD and a threatened status. If the range
of a taxon is suspected to be relatively circumscribed, and a considerable period of
time has elapsed since the last record of the taxon, threatened status may well be
justified.
26
i.
Not Evaluated (NE) : A taxon is Not Evaluated when it is has not yet been
evaluated against the criteria.
Note: As in previous IUCN categories, the abbreviation of each category (in
parenthesis) follows the English denominations when translated into other languages.
When discussing the IUCN Red List, the official term "threatened" is a grouping of
three categories: Critically Endangered, Endangered, and Vulnerable.
j.
Possibly Extinct : The additional category of Possibly Extinct (PE) is used by
Birdlife International, the Red List Authority for birds for the IUCN Red List.
Birdlife International has recommended PE become an official category. BirdLife
International has not stated whether a "Possibly Extinct in the Wild" category should
also be added, although it is mentioned that Spix's Macaw has this status. "Possibly
Extinct" can be considered a subcategory of "Critically Endangered".
3.6.4 Criticism
The IUCN Red List has come under criticism on the grounds of secrecy surrounding the
sources of data, among other allegations.
3.6.5 Mass extinctions
27
Apparent fraction of genera going extinct at any given time, as reconstructed from the
fossil record. Does not attempt to include recent Holocene extinction event.
There have been at least five mass extinctions in the history of life, and four in the last
3.5 billion years in which many species have disappeared in a relatively short period of
geological time. The most recent of these, the Cretaceous–Tertiary extinction event 65
million years ago at the end of the Cretaceous period, is best known for having wiped out
the non-avian dinosaurs, among many other species.
Modern mass extinction : According to a 1998 survey of 400 biologists conducted by
New York's American Museum of Natural History, nearly 70 percent believed that they
were currently in the early stages of a human-caused mass extinction, known as the
Holocene extinction event. In that survey, the same proportion of respondents agreed
with the prediction that up to 20 percent of all living populations could become extinct
within 30 years (by 2028). Biologist E. O. Wilson estimated in 2002 that if current rates
of human destruction of the biosphere continue, one-half of all species of life on earth
would be extinct in 100 years. More significantly the rate of species extinctions at present
is estimated at 100 to 1000 times "background" or average extinction rates in the
evolutionary time scale of planet Earth.
3.7
TERRESTRIAL BIODIVERSITY
Biodiversity is the web of life that distinguishes planet Earth from the other lifeless
spheres in our solar system, if not the universe. There are three different levels of
diversity: ecosystem diversity, species diversity, and genetic diversity (i.e., diversity
within species). We focus here on terrestrial (as opposed to aquatic) ecosystem diversity,
and on species diversity within terrestrial ecosystems.
The number and types of organisms inhabiting the planet have varied immensely during
geologic history. In part, these variations have been caused by the evolution of new types
of organisms and the elimination of others due to environmental changes and mass
extinctions, as occurred at the end of the Mesozoic period 65 million years ago which
saw the extinction of the dinosaurs.
Now, however, human transformations of the earth's surface are a force of geologic
proportions that is affecting biodiversity in almost every corner of the world. Changes are
occurring rapidly enough that the result is a net loss of species rather than a proliferation
of new life forms. Species have been disappearing at 50-100 times the natural rate, and
this is predicted to rise dramatically. Based on current trends, an estimated 34,000 plant
and 5,200 animal species - including one in eight of the world's bird species - are
critically endangered.
The greatest human impact on biodiversity is the alteration and destruction of habitats,
which occurs mainly through changes in land use: draining of wetlands, clearing of land
28
for agriculture, felling of forests for timber, and pollution of the environment and
fragmentation. Other impacts on biodiversity include the development and potential
proliferation of genetically modified organisms (GMOs), direct exploitation (e.g., overharvesting of plants or animals), and introduction of alien (non-native) species.
Loss of species is significant in several respects. First, breaking of critical links in the
biological chain can disrupt the functioning of an entire ecosystem and its
biogeochemical cycles. This disruption may have significant effects on larger scale
processes. Second, loss of species can have impacts on the organism pool from which
medicines and pharmaceuticals can be derived. Third, loss of species can result in loss of
genetic material, which is needed to replenish the genetic diversity of domesticated plants
that are the basis of world agriculture (Convention on Biological Diversity).
In recent years, the international scientific community has made considerable progress
toward fostering global awareness of the importance of biodiversity. As a result, a
number of multiagency organizations have been established, and many conservation
programs have been implemented.
3.8
BIODIVERSITY HOTSPOTS
A variety of approaches have been utilized to identify areas of high species richness and
endemism. A biodiversity hotspot is a biogeographic region with a significant reservior
of biodiversity that is threatened with destruction.
The concept of biodiversity hoptspots was originated by Dr. Norman Myers in two
articles in the scientific journal ‘The Environmentalist’ (1988 &1990) revised after
thorough analysis by myers and others in ‘Hotspots: Earth’s Biological Richest and Most
Endangered Terrestrial Ecoregions’ (1999). The hotspots ideas was also promoted by
Russell Mittermeier in the popular book ‘hotspots revisited’ (2004), although this has not
been subjected to scientific peer-review like the other hotspots analysis.
The term "hotspots" indicate areas of high conservation value that are facing significant
threats to conservation. Myer's first version was entirely focused on tropical rain forests.
In its most recent iteration, the hotspots analysis identified 25 high priority areas,
including some temperate areas such as the California coast, the Mediterranean and New
Zealand.
To qualify as a biodiversity hotspots, a region must two strict criteria : it must contain at
least 1,500 species of vascular plants as endemics, and it has to have lost at least 70 % of
its original habitat. Around the world, at least 25 areas qualify under this definition, with
nine other possible candidtes. These sites support nearly 60 % of the world’s plant, bird,
mammal, reptile, and amphibian species, with a very high share of endemic species.
29
Dense human habitation tends to occur near hotspots. Most hotspots are located in the
tropics and most of them are forests.
3.8.1 The biodiversity hotspots by region
North and Central America
1.
California Floristic Province
2.
Caribbean Islands
3.
Madrean Pine Oak Woodlands
4.
Mesoamerica
South America
1.
Atlantic Forest
2.
Cerrado
3.
Chilean Winter Rainfall-Valdivian Forests
4.
Tumes-Choco-Magdalena
5.
Tropical Andes
Europe and Central Asia
1.
Caucasus
2.
Irano-Anatolian
3.
Mediterranean Basin
4.
mountains of Central Asia
Africa
1.
Cape Floristic Region
2.
Coastal Forests of Eastern Africa
3.
Eastern Afromntane
4.
Guinean Forests of Eastern Africa
5.
Horn of Africa
6.
Coastal Forests of Eastern Africa
7.
Madagascar and the Indian Ocean Islands
8.
Maputaland Pondoland Albany
30
9.
Succulent Karoo
Asia – Pacific
1.
East Melanesian Island
2.
Eastern Himalaya
3.
Indo-Burma
4.
Japan
5.
Mountains of Southwest China
6.
New Caledonia
7.
New Zealand
8.
Philippines
9.
polynesia-Micronesia
10. Southwest Australia
11. Sundaland
12. Wallacea
13. Western Ghats and Sri Lanka
Brazil's Atlantic Forest is considered a hotspot of biodiversity and contains roughly
20,000 plant species, 1350 vertebrates, and millions of insects, about half of which occur
nowhere else in the world. The island of Madagascar including the unique Madagascar
dry deciduous forests and lowland rainforests possess a very high ratio of species
endemism and biodiversity, since the island separated from mainland Africa 65 million
years ago, most of the species and ecosystems have evolved independently producing
unique species different from those in other parts of Africa.
Many regions of high biodiversity (as well as high endemism) arise from very specialized
habitats which require unusual adaptation mechanisms. For example the peat bogs of
Northern Europe and the alvar regions such as the Stora Alvaret on Oland, Sweden host a
large diversity of plants and animals, many of which are not found elsewhere.
The Global 200 approach, adopted by the World Wide Fund for Nature (WWF),
identifies 233 high priority areas that are globally representative of all habitat types.
Olson and Dinerstein in 1998 suggest that although tropical moist forests contain over
half of all species diversity, the many other ecosystems that contain the remaining 50
percent also deserve consideration. These include tropical dry forests, tundra, temperate
grasslands, polar seas, and mangroves, which all contain unique expressions of
biodiversity with characteristic species, biological communities, and distinctive
ecological and evolutionary phenomena. Given their focus on ecoregions, large units of
31
land or water containing a characteristic set of natural communities, and given the large
number of regions included on the list, the Global 200 ecosystems comprises a much
larger proportion of the terrestrial land surface.
Hotspots and the Global 200 represent priority-setting efforts that focuses on high value
and highly threatened ecosystems. The Global 200 report states that, among terrestrial
ecosystems included on their list, 47 percent are considered critical or endangered and 29
percent are vulnerable, leaving a little over a quarter that are stable or intact. An
alternative approach, developed by Wildlife Conservation Society and CIESIN (2002), is
to identify the world's last great wild areas, and to concentrate resources and attention to
securing as much of those regions under some kind of conservation status. Presumably,
this can be done at far less cost than conservation in densely settled areas. Ultimately,
however, the two approaches are complimentary. The hotspots approach is undertaken in
combination with efforts to conserve the last remaining "pristine" wilderness areas.
3.8.2 Approaches to Biodiversity Conservation
There are some major approaches to conservation policy :
Traditional Protected Areas
Traditional protected areas harness the power of the state to define areas in which
varying degrees of conservation (from strict preservation to protected multi-use
landscapes), to set policies for land and resource use, and to enforce those policies
through allocation of resources and prosecution of offenders.
Collaborative Management
Collaborative management or community-based natural resource management works
with multiple stakeholders - government, community, and private sector - to identify and
implement approaches to conservation that may include varying degrees of sustainable
natural resource use. These two approaches are not mutually exclusive, and many
instances of collaborative management in and around protected areas have been
documented.
Conservation Corridor
There are also a number different approaches or theories that guide on-the-ground
conservation as it relates to land use and land cover. One of these is the development of
conservation corridors that connect a series of protected areas with protected landscapes
so as to provide animal migration routes in response to habitat fragmentation. In Central
America, which owing to its location as a land bridge between North and South America
contains some 7-8 percent of the world's biodiversity on just one percent of its land
surface, an ambitious initiative is underway to create a Mesoamerican Biological
32
Corridor (MBC). The MBC intends to use a combination of land purchases and
incentives to convince farmers living in the corridors to abandon slash and burn
agriculture and cattle ranching for planting shaded coffee and cacao, which an serve as
habitat for birds. Similar corridor initiatives have been undertaken to link habitat
remnants in Florida, and new initiatives are planned for Europe, western Australia, the
Himalayas, and Brazil's Amazon and Atlantic forests.
Gap Analysis
Gap analysis is a tool that was developed to identify the gaps between species
distribution and existing protected areas. In contrast to a species-by-species approach, or
habitat protection for a single flagship species (e.g., lions or pandas), gap analysis
identifies the gaps in representation of biodiversity in areas managed exclusively or
primarily for the long term maintenance of populations of native species and natural
ecosystems. Once identified, gaps are filled through new reserve acquisitions or
designations, corridors, or through changes in management practices.
Conservation of Agro-Biodiversity through Improved Land-Management
This is an important objective of the Convention on Biological Diversity. A dozen crops
together provide about 75 percent of the world's caloric intake. In terms of animal protein
intake, just three domestic animals - pigs, cattle and chickens - constitute the largest
sources. The importance of this greatly reduced number of crops and animals means that
conscious efforts will need to be taken to protect agro-biodiversity, if not for other reason
because little utilized or exploited crop varieties provide important genetic information
that can help to combat diseases and pests in the future. Some of the most valuable
genetic resources are in the fields of subsistence farmers in the developing world, and
countries like Mexico have made a conscious effort to exclude genetically modified
crops in order to preserve the purity of their local varieties.
3.9
BIODIVERSITY AND CLIMATE CHANGE
There are a number of major issues at the interface of biodiversity, land use and climate
change. As climate changes, ecosystems will respond to changes in temperature and
precipitation as well as changes in the carbon-dioxide concentrations in the atmosphere.
These changes are likely to favor some species and to negatively affect others, which will
alter competitive relationships and may cause invasions by "generalist" species (Walker
and Steffan 1997). Perhaps most significantly, there is a risk that climatic changes will
occur more rapidly than individual species are able to adapt. For those species that are
able to migrate with climate change (seeking appropriate habitat as it literally moves out
from under them), there is a risk that migration "escape routes" will be closed due to
anthropogenically altered landscapes or natural barriers, such as mountains, rivers and
oceans (Malcolm and Markham 2000). The ultimate result could be large-scale
extinctions.
33
An analysis of WWF's Global 200 ecosystems suggests that more than 80 percent of
these biologically rich regions will suffer extinctions of plant and animal species as a
result of global warming; changes in habitats from global warming will be more severe at
high latitudes and altitudes than in lowland tropical areas; the most unique and diverse
natural ecosystems may lose more than 70 percent of the habitats upon which their plant
and animal species depend; and many habitats will change at a rate approximately ten
times faster than the rapid changes during the recent postglacial period (Malcolm et al.
2002).
Unlike the introduction of invasive species, land conversion, and other threats to
biodiversity, because climate is globally pervasive, it will affect even remote wilderness
areas that to date have experienced little of anthropogenic change. Walker and Steffan
predict that more natural ecosystems will be in an early successional state, and that the
biosphere will be "weedier" and structurally simpler, by comparison with ecologically
complex old-growth areas. The study of climate change impacts on biodiversity is still in
its infancy, but several path breaking workshops and research initiatives suggest future
research directions for those interested in how humanity can mitigate the impacts of
climate change on other species (Global Change in Terrestrial Ecosystems, IAI 1994).
There is also increasing interest in how to address, at the policy level, the complex
linkages between climate change and biodiversity (IUCN 2001, Convention on
Biological Diversity).
3.10 LET US SUM UP
After going through this unit, you would have achieved the objectives stated earlier in the
unit. Let us recall what we have discussed so far.
1. Biodiversity Convention held at Rio-de-Janerio in June, 1992 has spelled out that the
variability among living organisms spring from all sources including terrestrial,
marine and freshwater ecosystems and also the ecological complexes of which they
are part. Para et al. (1993) has thus spelled out three types of diversities viz. α (alpha),
β (beta) and γ (gamma);
2. Diversity is the most important characteristic of nature, which pervades the whole
universe. The planet earth also exhibits a wide range of diversity both amongst
inanimate and animate objects. Animate objects exhibits much greater diversity than
the same exhibited by inanimate objects;
3. The environmental concerns of the present day are fundamentally governed by the
biodiversity. A voyage through the area of history of living organisms on this planet
reveals that ever since the birth of life on this lifeless earth of ours and throughout the
evolutionary process the diversity has played an important role in the integration and
maintenance of the system;
34
4. Species must adapt to environmental change to survive. Species are reproductive
communities, with their members capable of interbreeding among themselves, and
not, as the general rule, with members of other species.
5. Evolution of new species centers on how changes occur in adaptations so that an
ancestral species is split into two (occasionally more) descendant species, with
interbreeding no longer possible between the members of what have evolved into
descendant, or “daughter,” species.
6. Speciation, then, is integral to the evolutionary process. Natural selection shapes most
evolutionary adaptive change nearly simultaneously in genetically independent
lineages as speciation is triggered by extinction in “turnover” events. When physical
environmental events that go “too far too fast” start triggering regional, species-level
extinction, then evolutionary change predominantly via speciation occurs. In times of
environmental normalcy, speciation and species-wide evolutionary change are
comparatively rare;
7. The reduction of biodiversity results in the disruption of the quality and quantity of
services provided at various trophic levels in an ecosystem. Such stressed ecosystems
have to be managed so that at all stages and at all times the balance remains intact
and the system functions unhindered;
8. Number of factors like misuse of nature, destruction and degradation of forests and
habitats, contamination and destruction of natural resources is leading to the
extinction of several species of organisms;
9. India is one of the 12-mega biodiversity countries of the world and currently
available data place India in the tenth position in the world and fourth in Asia in plant
diversity. In terms of the number of mammalian species, India ranks tenth in the
world and ranks eleventh for endemic species of higher vertebrates. India have two of
the all identified ‘Hot Spots’. These are Eastern Himalayan and Western Ghats.
3.11 CHECK YOUR PROGRESS : THE KEY
Tick the correct answer :
1. Species content of a region irrespective of numerical strength of each species is
called :
(a) Vegetation
(b) Flora
(c) Community
(d) None of these
2. According to IUCN what percentage of flowering plants in world is endangered ?
(a) 50 %
(b) 15 %
(c) 10 %
(d) 05 %.
3. The tendency of biological system to remain in a state of equilibrium is called
(a) Biomass
(b) Succession
35
(c) Post - climax
(d) Homeostasis
4. The species that occur in different geographical regions are called :
(a) Sympatric
(b) Allopatric
(c) Ecological equivalents
(d) None of the above
5. Which is the most stable ecosystem ?
Key :
1.
2.
3.
4.
5.
3.12
(a) Desert
(b) Ocean
(c) Mountain
(d) Forests
(b) Flora
(c) 10 %
(d) Homeostasis
(b) Allopatric
(b) Ocean
ASSIGNMENTS/ ACTIVITIES
It is compulsory for every student to complete an assignment/ activity/ project work from
any known prospects of present study of biological diversity. Explain the following (any
one):
1. Biological diversity and its phases of evolution in India.
2. Ecological amplitudes and possible way, which a species can extend its distribution
to newer areas in nature.
3. Species speciation and mode of distribution.
4. IUCN categories of threat
5. Biodiversity hot spots and approaches to conservation,
6. Terrestrial biodiversity
3.13 REFERENCES / FURTHER READINGS

Agarwal A (1992). Jhum: Is there a way out? The price of forests. CSE, New Delhi.

Alexander VM and Korotayev AV (2007). Phanerozoic marine biodiversity follows a
hyperbolic trend. Palaeoworld 16: 311-318.

Alroy J (2001). Effect of sampling standardization on estimates of Phanerozonic marine
diversification. Proceedings of the National Academy of Science, USA 98: 6261-6266.

Bloom DE (1995). International Public Opinion on the Environment. Science 269: 354357.
36


Chandra S, Khanna KK and Kehri HK (1995). Microbes and Man. BSMPL Publishers,
Dehra Dun, India.
Chaterjee S (1995). Global ‘Hot Spots’ of Biodiversity. Current Science 68:11778-1179.

Clover C (2004). The End of the Line: How overfishing is changing the world and what
we eat. Ebury Press, London.

Davis P and Kenrick P (2004). Fossil Plants. Smithsonian Books, Washington DC.

Diamond J (1999). Up to the Starting Line: Guns, Germs, and Steel. WW Norton.

Drakare Stina, Lennon JJ, Hillebrand Helmut (2006). The imprint of the geographical,
evolutionary and ecological context on species-area relationships. Ecology Letters 9: 215227.

Edward OW (2002). The Future of Life. Alfred A. Knopf, New York.

Encyclopedia Smithsonian: Numbers of Insects

Gadgil M (1994). Reckoning with life. The Hindu Survey of the Environment.

Gaston KJ and Spicer JI (2004). Biodiversity: an introduction. 2nd Ed, Blackwell
Publishing.

Government of India (1994). Conservation of Biological Diversity in India: An
Approach. MoEF, GOI, New Delhi pp 48.

Green JB (1993). Natural Resources of the Himalaya and the Mountains of Central Asia.
IUCN, Gland, Switzerland. pp. 137-290.

IUCN (2004). IUCN Red List of Threatened Species. International Union for the
Conservation of Nature and Natural Resources and World Conservation Union, Gland,
Switzerland.

IUCN (2007). IUCN Red List of Threatened Species. International Union for the
Conservation of Nature and Natural Resources and World Conservation Union, Gland,
Switzerland.

Klemn C (1993). Biological Diversity, Conservation and Law. IUCN, Gland,
Switzerland.

Lawton JH and May RM. Extinction rates, Oxford University Press, Oxford, UK.

Lee Anita (2007). The Pleistocene Overkill Hypothesis. University of California at
Berkeley Geography Programme.

Leveque C and Mounolou J (2003). Biodiversity. John Wiley & Sons New York.

Margulis L, Dolan D K and Lyons C. Diversity of Life: The Illustrated Guide to the Five
Kingdoms. Jones & Bartlett Publishers, Sudbury.

Myers N (1988). Threatened biotas: 'hot spots' in tropical forests. Environmentalist 8:
187-208.

Myers N (1990). The biodiversity
Environmentalist 10: 243-256.
challenge:
expanded
hot-spots
analysis.
37

Myers N, Mittermeier RA, Mittermeier CG, Fonseca GABda and Kent J (2000).
Biodiversity hotspots for conservation priorities. Nature 403: 853-858.

Nee S (2004). More diverse than meets the eye. Nature 429: 804-805.

Novacek MJ (2001). The Biodiversity Crisis: Losing What Counts. American Museum of
Natural History Books, New York.

Pant DD (1999). Biodiversity Conservation and Evolution of Plants. Current Science 76:
21-23.

Payne JL and Finnegan S (2007). The effect of geographical range on extinction risk
during background and mass extinction. Proc. Nat. Acad. Sci. 104: 10506-10511.

Possingham H and Wilson K (2005). Turning up the heat on hotspots. Nature 436: 919920.

Stork NE (2007). Biodiversity: world of Insects. Nature 448: 657-658.

Whittaker RH (1972). Evolution and measurement of species diversity. Taxon 21: 213251.

Wilson EO (1988). The current state of Biological Diversity. In: Biodiversity. National
Academy Press, Washington DC pp. 3-5.

World Conservation Monitoring Center (1992). Global Biodiversity: Status of Earth’s
Living Resources. Chapman and Hall, London.

World Conservation Monitoring Center (1993). Global Biodiversity. Chapman and Hall,
London.

World Resources Institute (1992). World Resources, 1992-93. Oxford University Press,
New York.
38
UNIT 4 POLLUTION & CLIMATE CHANGE
Structure
4.0
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
Introduction
Objectives
Major Forms of Pollution and major Polluted Areas
Air Pollution
4.3.1 Pollutants
4.3.2 Sources
4.3.3 Indoor Air Quality or Indoor Air Pollution
4.3.4 Effects of Air Pollution
4.3.5 Reduction Efforts
Water Pollution
4.4.1 Sources
4.4.2 Contaminants
4.4.3 Transport and Chemical Reaction of Water Pollution
4.4.4 Effects of Water Pollution
Soil Pollution
4.5.1 Microanalysis of Soil Contamination
4.5.2 Effects on Human Health
4.5.3 Effects on Ecosystem
4.5.4 Cleanup Options
Greenhouse Gases
4.6.1 Greenhouse Effect
4.6.2 Greenhouse Gases : Trends and Role
4.6.3 Sources of the Greenhouse Gases
4.6.4 Greenhouse Gas Emission
4.6.5 Role of Greenhouse Gases in Climate Change
Ozone Layer
4.7.1 Origin
4.7.2 Distribution of Ozone in Stratosphere
4.7.3 Importance of Ozone layer
4.7.4 Regulation
Ozone Hole or Ozone Depletion
4.8.1 Ozone Depletion mechanism
4.8.2 Consequence of Ozone Layer Depletion
4.8.3 Ozone Depletion and Global Warming
Global Warming
4.9.1 Terminology
4.9.2 Recent Temperature Changes
4.9.3 Cause of Global Warming
4.9.4 Feedbacks
4.9.5 Attributed and expected effects
Ultraviolet
4.10.1 Discovery
4.10.2 Origin of term
39
4.10.3
4.10.4
4.10.5
4.10.6
4.10.7
4.10.8
4.10.9
4.11
4.12
4.13
4.14
4.15
Subtypes
Black light
Natural sources of UV
Human Health related Effects of UV Radiation
Degradation of Polymers, Pigments and Dyes
Blockers and Absorbers
Application of UV
Sea Level Rise
4.11.1 Overview of Sea Level Rise
4.11.2 Effects of Sea level Rise
4.11.3 Sea Level Measurement Through Satellite
Let Us Sum Up
Check Your Progress & the Key
Assignments / Activities
References / Further Readins
40
4.1
INTRODUCTION
Pollution is the introduction of contaminants into an environment. These contaminants
cause instability, disorder, harm or discomfort to the physical systems or living
organisms therein. Pollution can take the form of chemical substances, or energy, such as
noise, heat, or light energy. Pollutants, the elements of pollution, can be foreign
substances or energies, or naturally occurring; when naturally occurring, they are
considered contaminants when they exceed natural levels. Pollution is often classed as
point source or nonpoint source pollution.
Sometimes the term pollution is extended to include any substance when it occurs at such
unnaturally high concentration within a system that it endangers the stability of that
system. For example, water is innocuous and essential for life, and yet at very high
concentration, it could be considered a pollutant: if a person were to drink an excessive
quantity of water, the physical system could be so overburdened that breakdown and
even death could result.
4.2
Objectives
The main aim of this unit is give you an overall picture of present scenario of
environmental pollution and its effects on biosphere. The major objectives of present
study are:
1. to understand the environmental pollution and its effects on air, water and soil;
2. to identification and characterisation of pollutants, critical environmental variables
and key species of pollutant gradients;
3. to study the cycling of pollutants within ecosystem;
4. to understand the structure of ozone layer and its depletion;
5. to understand about global warming, ultraviolet and sea level rise and
6. to understand the economically sound and environmentally robust solutions to control
global climatic problems.
4.3
MAJOR FORMS
POLLUTED AREAS
OF
POLLUTION
AND
MAJOR
The major forms of pollution are listed below along with the particular pollutants
relevant to each of them:

Air pollution, the release of chemicals and particulates into the atmosphere.
Common air pollutants include carbon monoxide, sulfur dioxide, chlorofluorocarbons
(CFCs) and nitrogen oxides produced by industry and motor vehicles. Photochemical
ozone and smog are created as nitrogen oxides and hydrocarbons react to sunlight.

Water pollution, by the release of waste products and contaminants into surface
runoff into river drainage systems, leaching into groundwater, liquid spills,
wastewater discharges, eutrophication and littering.
41

Soil contamination occurs when chemicals are released by spill or underground
leakage. Among the most significant soil contaminants are hydrocarbons, heavy
metals, MTBE, herbicides, pesticides and chlorinated hydrocarbons.

Radioactive contamination, resulting from 20th century activities in atomic physics,
such as nuclear power generation and nuclear weapons research, manufacture and
deployment.

Noise pollution, which encompasses roadway noise, aircraft noise, industrial noise as
well as high-intensity sonar.

Light pollution, includes light trespass, over-illumination and astronomical
interference.

Visual pollution, which can refer to the presence of overhead power lines, motorway
billboards, scarred landforms (as from strip mining), open storage of trash or
municipal solid waste.

Thermal pollution, is a temperature change in natural water bodies caused by human
influence, such as use of water as coolant in a power plant.
The Blacksmith Institute issues annually a list of the world's worst polluted places. In the
2007 issues the ten top nominees are located in Azerbaijan, China, India, Peru, Russia,
Ukraine and Zambia.
4.4
AIR POLLUTION
Air pollution is the human introduction into the atmosphere of chemicals, particulate
matter, or biological materials that cause harm or discomfort to humans or other living
organisms, or damage the environment. Air pollution causes deaths and respiratory
disease. Air pollution is often identified with major stationary sources, but the greatest
source of emissions is actually mobile sources, mainly automobiles. Gases such as
carbon dioxide, which contribute to global warming, have recently gained recognition as
pollutants by climate scientists, while they also recognize that carbon dioxide is essential
for plant life through photosynthesis.
The gaseous cover on the surface of the earth is called atmosphere. The atmosphere is a
complex, dynamic natural gaseous system that is essential to support life on planet
Earth.. It consists of gaseous mixtures such as nitrogen, oxygen, carbon dioxidemixed
with water vapours and is collectively called air. According to Sytnick, (1985), the
gaseous mass wchich forms the atmosphere is about 5.5 x 1015 tons. It also contains other
gases in very minute quntitiy, dust particle, pollen grains etc., which are given in
following tables :
Composition of Unpolluted Air
Consitituents
Nitrogen
Oxygen
Argon
Volume
78.09 %
20.94 %
0.93 %
42
Carbon dioxide
Neon
Helium
Methane
Krypton
Hydrogen
Nitrous oxides
Carbon mono-oxide
Ozone
Sulphure dioxide
Nitrogen dioxide
4.4.1
0.032 %
18 ppm
5.2 ppm
1.3 ppm
1.0 ppm
0.5 ppm
0.25 ppm
0.1 ppm
0.02 ppm
0.001 ppm
0.001 ppm
Pollutants
There are so many substances in the air which may impair the health of living beings, or
reduce visibility. These arise both from natural processes and human activity. Substances
not naturally found in the air or at greater concentrations or in different locations from
usual are referred to as pollutants.
Pollutants can be classified as either primary or secondary. Primary pollutants are
substances directly emitted from a process, such as ash from a volcanic eruption or the
carbon monoxide gas from a motor vehicle exhaust.
Secondary pollutants are not emitted directly. Rather, they form in the air when primary
pollutants react or interact. An important example of a secondary pollutant is ground
level ozone - one of the many secondary pollutants that make up photochemical smog.
Note that some pollutants may be both primary and secondary: that is, they are both
emitted directly and formed from other primary pollutants.
Major primary pollutants produced by human activity include:

Sulfur oxides (SOx) especially sulfur dioxide are emitted from burning of coal and
oil.

Nitrogen oxides (NOx) especially nitrogen dioxide are emitted from high temperature
combustion. Can be seen as the brown haze dome above or plume downwind of
cities.

Carbon monoxide is colourless, odourless, non-irritating but very poisonous gas. It is
a product by incomplete combustion of fuel such as natural gas, coal or wood.
Vehicular exhaust is a major source of carbon monoxide.

Carbon dioxide (CO2), a greenhouse gas emitted from combustion.

Volatile organic compounds (VOC), such as hydrocarbon fuel vapors and solvents.

Particulate matter (PM), measured as smoke and dust. PM10 is the fraction of
suspended particles 10 micrometers in diameter and smaller that will enter the nasal
43
cavity. PM2.5 has a maximum particle size of 2.5 µm and will enter the bronchies
and lungs.

Toxic metals, such as lead, cadmium and copper.

Chlorofluorocarbons (CFCs), harmful to the ozone layer emitted from products
currently banned from use.

Ammonia (NH3) emitted from agricultural processes.

Odors, such as from garbage, sewage, and industrial processes

Radioactive pollutants produced by nuclear explosions and war explosives, and
natural processes such as radon.
Secondary pollutants include:

Particulate matter formed from gaseous primary pollutants and compounds in
photochemical smog, such as nitrogen dioxide.

Ground level ozone (O3) formed from NOx and VOCs.

Peroxyacetyl nitrate (PAN) similarly formed from NOx and VOCs.
Minor air pollutants include:

4.4.2
A variety of persistent organic pollutants, which can attach to particulate matter are
known as minor hazardous air pollutants. Some of these are regulated in USA under
the Clean Air Act and in Europe under the Air Framework Directive..
Sources
Sources of air pollution refer to the various locations, activities or factors which are
responsible for the releasing of pollutants in the atmosphere. These sources can be
classified into two major categories which are :
Anthropogenic sources : Its include human activity mostly related to burning different
kinds of fuel.

"Stationary Sources" as smoke stacks of power plants, manufacturing facilities,
municipal waste incinerators.

"Mobile Sources" as motor vehicles, aircraft etc.

Marine vessels, such as container ships or cruise ships, and related port air pollution.

Burning wood, fireplaces, stoves, furnaces and incinerators .

Oil refining, and industrial activity in general.

Chemicals, dust and controlled burn practices in agriculture and forestry
management.

Fumes from paint, hair spray, varnish, aerosol sprays and other solvents.

Waste deposition in landfills, which generate methane.
44

Military, such as nuclear weapons, toxic gases, germ warfare and rocketry.
Natural sources

Dust from natural sources, usually large areas of land with little or no vegetation.

Methane, emitted by the digestion of food by animals, for example cattle.

Radon gas from radioactive decay within the Earth's crust.

Smoke and carbon monoxide from wildfires.

Volcanic activity, which produce sulfur, chlorine, and ash particulates.
Emission factors
Air pollutant emission factors are representative values that attempt to relate the quantity
of a pollutant released to the ambient air with an activity associated with the release of
that pollutant. These factors are usually expressed as the weight of pollutant divided by a
unit weight, volume, distance, or duration of the activity emitting the pollutant (e.g.,
kilograms of particulate emitted per megagram of coal burned). Such factors facilitate
estimation of emissions from various sources of air pollution. In most cases, these factors
are simply averages of all available data of acceptable quality, and are generally assumed
to be representative of long-term averages.
4.4.3
Indoor Air Quality (IAQ) or Indoor Air pollution
It refers to the physical, chemical, and biological characteristics of air in the indoor
environment within a home, building, or an institution or commercial facility. Indoor air
pollution is a concern in the developed countries, where energy efficiency improvements
sometimes make houses relatively airtight, reducing ventilation and raising pollutant
levels. Indoor air problems can be subtle and do not always produce easily recognized
impacts on health. Different conditions are responsible for indoor air pollution in the
rural areas and the urban areas.
In the developing countries, it is the rural areas that face the greatest threat from indoor
pollution, where some 3.5 billion people continue to rely on traditional fuels such as
firewood, charcoal, and cowdung for cooking and heating. Concentrations of indoor
pollutants in households that burn traditional fuels are alarming. Burning such fuels
produces large amount of smoke and other air pollutants in the confined space of the
home, resulting in high exposure. Women and children are the groups most vulnerable as
they spend more time indoors and are exposed to the smoke. Daily averages of pollutant
level emitted indoors often exceed current WHO guidelines and acceptable levels.
Although many hundreds of separate chemical agents have been identified in the smoke
from biofuels, the four most serious pollutants are particulates, carbon monoxide,
polycyclic organic matter, and formaldehyde. Unfortunately, little monitoring has been
done in rural and poor urban indoor environments in a manner that is statistically
rigorous.
45
In urban areas, exposure to indoor air pollution has increased due to a variety of reasons,
including the construction of more tightly sealed buildings, reduced ventilation, the use
of synthetic materials for building and furnishing and the use of chemical products,
pesticides, and household care products. Indoor air pollution can begin within the
building or be drawn in from outdoors. Other than nitrogen dioxide, carbon monoxide,
and lead, there are a number of other pollutants that affect the air quality in an enclosed
space.
Volatile organic compounds originate mainly from solvents and chemicals. The main
indoor sources are perfumes, hair sprays, furniture polish, glues, air fresheners, moth
repellents, wood preservatives, and many other products used in the house. The main
health effect is the imitation of the eye, nose and throat. In more severe cases there may
be headaches, nausea and loss of coordination. In the long term, some of the pollutants
are suspected to damage to the liver and other parts of the body.
Tobacco smoke generates a wide range of harmful chemicals and is known to cause
cancer. It is well known that passive smoking causes a wide range of problems to the
passive smoker (the person who is in the same room with a smoker and is not
himself/herself a smoker) ranging from burning eyes, nose, and throat irritation to cancer,
bronchitis, severe asthma, and a decrease in lung function.
Pesticides, if used carefully and the manufacturers, instructions followed carefully they
do not cause too much harm to the indoor air.
Biological pollutants include pollen from plants, mite, hair from pets, fungi, parasites,
and some bacteria. Most of them are allergens and can cause asthma, hay fever, and other
allergic diseases.
Formaldehyde is a gas that comes mainly from carpets, particle boards, and insulation
foam. It causes irritation to the eyes and nose and may cause allergies in some people.
Asbestos is mainly a concern because it is suspected to cause cancer.
Radon (Rn) gas, a carcinogen, is exuded from the earth in certain locations and trapped
inside houses. Due to modern houses having poor ventilation, it is confined inside the
house causing harm to the dwellers.
4.4.4
Effects of air pollution
The important effects of air pollutants are as follows :
1. Atmospheric particles can scatter and absorbed sunlight, thus reduce the visibility.
Reduced visibility is aesthetically unidesirable and it is also dangerous for aircrafts
and motors. In general cities receive above 15 to 20 % less solar radiation than rural
areas and the reduction of sunlight can become as high as one third in the summer
and two-third in winter. The reduction in sunlight is largely due to fuel combustion
for industrial and household heating purpose.
46
2. The effects of particulate matter include corrosion of metals, erosion and soiling of
buildings, soulptures and painted surfaces and soiling of clothings and draperies,
damage of electric equipments etc.
3. The toxic effects of particulate matter on animals and human beings can be classified
as :



Intrinsic toxicity due to chemical or physical properties - Carbon monoxide in
congested areas remove 5 to 10 %of blood from circulation. Although body
tissues extract only 25 % of O2 from the blood, the heart needs 75%. So there is
little margin for safety.
Interference with clearance mechanism in the respiratory tracts - Chronic
bronchitis and emphysma have also been found to caused by SO2. a 24 hour
exposure to about 0.2 ppm of SO2 may cause serious health problems. Lung
cancer has also been found to correlated with air pollution. Polycyclic aromatic
hydrocarbons (PAH) are found to related to the pathogenesis of lung cancer.
Toxicity due to abosrbed toxic substance – Many toxic particles includings
metal dusts, asbestos, aromatic hydrocarbons have been discovered in a polluted
urban atmosphere. Lead from vehicle exhaustsa, resulting from the use of
tetraethyl lead as an anti knock additive to petrol, may build up to dangerous
levels in urban areas adacent to busy road complexes. Lead in high doses kills
outright. In lower doses (in dense traffic areas) it shortens life span and causes
deterioration of nervous system. Retarded children have a higher lead conteneet in
their body than the normal ones.
4. Benzpyrenes – Their concentrations are extremely small but they play a role in higher
cancer rates in urban areas as compared to rural areas. Peroxy acetyl nitrates (PAN)
or photochemical smog may constitute a serious problem where high levels of
vehicular emmissions occur in cities experiencing bright sunlight and ambient
temperatures above 21oC.
5. The small solid particles can serve as carriers for microorganisms and other infective
agents and therby spread diseases. Large dust particles are trapped in nose and
throat and very tiny particles which stay in the lungs may start an ugly chain of events
leading to serious illness and deaths.
6. Air pollution causes coughing, sneezing, thickening of secretion of mucus and
narrowing or complete closure of glottis due to presence of gases, especially SO2,
nitrogen dioxide and oxidaqnts. The silicon particles may cause ‘silicosis’ and fibrous
particles ‘fibrosis’. It is suspected that some pollutants can start the growth of lung
cancer.
7. Effect of SO2 – SO2 can damage materials and properties mainly through their
conversion into the highly reactive H2SO4. It causes discolouration and physical
deteriation of building materials and sculptures. Deterioration and fading are also
produced in fabrics as cotton, nylon, leather and paper. It accelerates corrosion of
metals, especially iron, steel and zinc. SO2 and H2SO4 both are capable of causing
irritation in respiratory tracts of animals and human beings and high concentrations of
SO2 cause severe heart and lung diseases.
8. The toxic effects of CO on human beings or animals arise from its reversible
combination with haemoglobin in the blood. Haemoglobin has much greater affinity
47
with CO and it lessens the oxygen carrying capacity of blood. It also reduces the
dissociation of oxyhaemoglobin.
9. A continued increase in excess unabsorbed CO2 could have a catastrophic warming
effect on the atmosphere, melting of polar ice, change in the ecosystems of seas and
even floods on an undreamed scale.
10. Effect of NO2 – Nitrogen oxides are known to produce fading the textile dyes,
deterioration of cotton and nylon and corrosion of metals due to production of
particulate nitrates. It affects lungs, heart, liver and kidney at higher concentrations
(15 to 50 ppm for two hours). Besides, it is considered to be a major factor in causing
eye irrittaion.
11. Effects of air pollutants on plants – SO2 has been found to affect vegetation
adversely even at the concentration below 0.032 ppm. It is suspected that sulphur
dioxide pollution in urban and industrial areas of industrialised countries has a major
impact on the respiratory condition of the population and also has significant effects
on the crops and other vegetations of the surrounding rural areas. High concentration
of SO2 over short period of time can produce leaf injury, such as necrosis in plants or
brownish colouration in the tips of pine needles. Lower concentrations over long
period lead to chronic leaf injury such as gradual chlorosis. NO2 also causes leaf
injury and reduction of growth in several NO2 sensitive plants. Some plants produce
volatile tarpenbes. In urban areas, ethylene (a hydrocarbon) is known to inhibit the
plant growth.
4.4.5
Reduction efforts
There are various air pollution control technologies and urban planning strategies
available to reduce air pollution.
Efforts to reduce pollution from mobile sources includes primary regulation (many
developing countries have permissive regulations), expanding regulation to new sources
(such as cruise and transport ships, farm equipment, and small gas-powered equipment
such as lawn trimmers, chainsaws, and snow mobiles), increased fuel efficiency (such as
through the use of hybrid vehicles), conversion to cleaner fuels (such as bioethanol,
biodiesel, or conversion to electric vehicles).
4.5
WATER POLLUTION
Water pollution is the contamination of water bodies such as lakes, rivers, oceans, and
groundwater caused by human activities, which can be harmful to organisms and plants
which live in these water bodies. Water pollution is a major problem in the global
context. It has been suggested that it is the leading worldwide cause of deaths and
diseases, and that it accounts for the deaths of more than 14,000 people daily.
Although natural phenomena such as volcanoes, algae bloom, storms, and earthquakes
also cause major changes in water quality and the ecological status of water. Water is
typically referred to as polluted when it impaired by anthropogenic contaminants and
either does not support a human use (like serving as drinking water) or undergoes a
48
marked shift in its ability to support its constituent biotic communities. Water pollution
has many causes and characteristics.
4.5.1
Sources
The primary sources of water pollution are generally grouped into two categories based
on their point of origin. Point-source pollution refers to contaminants that enter a
waterway through a discrete "point source". Examples of this category include discharges
from a wastewater treatment plant, outfalls from a factory, leaking underground tanks,
etc.
The second primary category, “non-point source” pollution, refers to contamination that,
as its name suggests, does not originate from a single discrete source. Non-point source
pollution is often a cumulative effect of small amounts of contaminants gathered from a
large area. Nutrient runoff in stormwater from sheet flow over an agricultural field, or
metals and hydrocarbons from an area with high impervious surfaces and vehicular
traffic are examples of non-point source pollution. The primary focus of legislation and
efforts to curb water pollution for the past several decades was first aimed at point
sources. As point sources have been effectively regulated, greater attention has come to
be placed on non-point source contributions, especially in rapidly urbanizing/
suburbanizing or developing areas.
4.5.2
Contaminants
The specific contaminants leading to pollution in water include a wide spectrum of
chemicals, pathogens, and physical or sensory changes. While many of the chemicals and
substances that are regulated may be naturally occurring (iron, manganese, etc) the
concentration is often the key in determining what is a natural component of water, and
what is a contaminant. Many of the chemical substances are toxic. Pathogens can
produce waterborne diseases in either human or animal hosts. Alteration of water's
physical chemistry include acidity, electrical conductivity, temperature, and
eutrophication.
Contaminants may include organic and inorganic substances.
Organic water pollutants are:

Insecticides and herbicides, a huge range of organohalide and other chemicals

Bacteria, often is from sewage or livestock operations

Food processing waste, including pathogens

Tree and brush debris from logging operations

VOCs (volatile organic compounds), such as industrial solvents, from improper
storage
49

DNAPLs (dense non-aqueous phase liquids), such as chlorinated solvents, which may
fall at the bottom of reservoirs, since they don't mix well with water and are more
dense

Petroleum Hydrocarbons including fuels (gasoline, diesel, jet fuels, and fuel oils) and
lubricants (motor oil) from oil field operations, refineries, pipelines, retail service
station's underground storage tanks, and transfer operations. Note: VOCs include
gasoline-range hydrocarbons.

Detergents

Various chemical compounds found in personal hygiene and cosmetic products

Disinfection by-products (DBPs) found in chemically disinfected drinking water
Inorganic water pollutants include:
4.5.3

Heavy metals including acid mine drainage

Acidity caused by industrial discharges (especially sulfur dioxide from power plants)

Pre-production industrial raw resin pellets, an industrial pollutant

Chemical waste as industrial by products

Fertilizers, in runoff from agriculture including nitrates and phosphates

Silt in surface runoff from construction sites, logging, slash and burn practices or land
clearing sites
Transport and chemical reactions of water pollutants
Most water pollutants are eventually carried by the rivers into the oceans. In some areas
of the world the influence can be traced hundred miles from the mouth by studies using
hydrology transport models. Advanced computer models such as SWMM or the DSSAM
Model have been used in many locations worldwide to examine the fate of pollutants in
aquatic systems.
Many chemicals undergo reactive decay or chemically change especially over long
periods of time in groundwater reservoirs. A noteworthy class of such chemicals are the
chlorinated hydrocarbons such as trichloroethylene (used in industrial metal degreasing
and electronics manufacturing) and tetrachloroethylene used in the dry cleaning industry.
Both of these chemicals, which are carcinogens themselves, undergo partial
decomposition reactions, leading to new hazardous chemicals (including
dichloroethylene and vinyl chloride).
Groundwater pollution is much more difficult to abate than surface pollution because
groundwater can move great distances through unseen aquifers. Non-porous aquifers
such as clays partially purify water of bacteria by simple filtration (adsorption and
absorption), dilution, and, in some cases, chemical reactions and biological activity:
however, in some cases, the pollutants merely transform to soil contaminants.
Groundwater that moves through cracks and caverns is not filtered and can be transported
50
as easily as surface water. In fact, this can be aggravated by the human tendency to use
natural sinkholes as dumps in areas of Karst topography.
There are a variety of secondary effects stemming not from the original pollutant, but a
derivative condition. Some of these secondary impacts are:
4.5.4

Silt bearing surface runoff from can inhibit the penetration of sunlight through the
water column, hampering photosynthesis in aquatic plants.

Thermal pollution can induce fish kills and invasion by new thermophilic species.
This can cause further problems to existing wildlife.
Effects of Water Pollution
Water Pollution comes from many different sources and can effect many different things.
The effects of water pollution are not only devastating to people, but they can kill
animals, fish, and birds. Furthermore, the effects of water pollution pose a serious threat
to society today and in the future.
Effects of Untreated Human Waste
Normally, human waste goes through various treatment plants to become
uncontaminated, but during a heavy rain storm, human waste can back up and overflow
into rivers or the water supplies. This waste can also cause disease and it can rob the
water of oxygen which kills the wildlife that lives in the water.
Effects of Run-Off Pollution
When rain runs off the land it picks up dirt and silt and carries them into the water. When
the dirt and silt (sediment) settle in the water body they enter, these sediments can keep
sunlight from reaching aquatic plants, plants that live in and grow in the water. When the
sun can't reach the plants, they die. The sediments can also clog fish gills, and some other
organisms that live on the bottom of the body of water.
Effects of Oil Pollution and Antifreeze
When oil is spilled into the water, the effects on the ecosystem and its components are
devastating. Some animals, such as birds, mammals, and fish may and can be killed if
they ingest oil. Many may die from eating oil contaminated prey. Birds may die if the oil
coats their feathers. They can neither fly nor stay warm. Furthermore, when oil coats the
feathers they can become sick and die. Oil and antifreeze can cause the water to have a
bad odor and leave a sticky film on the surface of water that kills animals and fish. Oil is
one of the most devastating pollutants of water. Contaminated Ground Water Effects
When contaminated water seeps into the ground it can have serious effects. People can
get very sick and have the possibility of developing liver or kidney problems, cancer or
other illnesses, depending on if contaminated water seeps into the ground.
51
Fertilizers and Other Chemicals
Water, from rain, runs down the slopes of the land which may include farm areas that use
fertilizers, pesticides, and other farming chemicals. After that they travel down into the
rivers, lakes, or oceans. Fertilizers and some chemicals may cause plants to grow quicker.
With the growth of more plants, more bacteria will grow (bacteria eat dead plants).
Bacteria need oxygen to survive and if there are more bacteria in a river than normal,
there is less oxygen for fish and some of them may die. In addition, some fish in the
Great Lakes suffer from tumors and the populations of some species in these waters are
declining. Other chemicals besides farming chemicals effect humans as well. Nitrates in
drinking water can cause diseases to infants that might cause them death. Cadmium (a
metal in sludge-derived fertilizer) can be absorbed by crops, and if people ingest this in
sufficiently it can cause diarrheal disorders, liver, and kidney damage. The culprit is
suspected to be inorganic substances such as mercury, arsenic, and lead. Also, other
chemicals can cause problems with the taste, smell, and the color of water. Pesticides,
PCB's, and PCP's (polychlorinated phenols) are some examples that are toxic to all life.
Pesticides are used in farming, forestry, and homes. PCB's can still be found as insulators
in old electrical transformers, and PCP's can be found in products such as wood
preservatives. They are very toxic and that is what makes them a threat to our ecosystem.
Effects of Factory Pollution
Many factories have pipes that drain chemicals into rivers or streams. These chemicals
can damage aquatic life as they are carried downstream. Furthermore, the added
chemicals can warm the river, which decreases the amount of oxygen that the fish need to
live.
Effects of Garbage from Private Offices and Homes
Many people today dump their garbage into streams, lakes, rivers, and oceans. Some
examples of this garbage are cans, paper, furniture, and other household products. When
people dump cleaning products into the ecosystem they are endangering its inhabitants.
When plastic is dumped in lakes, ducks are at risk because they might be strangled and
when dumped in the ocean, dolphins might be killed. Aluminum cans can cut the animals
and fish.
Effects of Eutrophication
Eutrophication is the fertilization of surface water by nutrients that were previously
scarce. Eutrophication, occurs when lake water is artificially supplemented with
nutrients, which causes abnormal plant growth. The cause of eutrophication can be runoff
of chemical fertilizers from fields. Eutrophication can produce problems such as bad
tastes and odors as well as green scum algae. Also, the growth of rooted plants increases,
which decreases the amount of oxygen in the deepest waters of the lake. A common
chemical change is the precipitation of calcium carbonate in hard waters. Eutrophication
makes some lakes void of life.
Effects of Acid Rain
52
The effects of acid rain are most clearly seen in lakes, streams, rivers, oceans, and other
bodies of water. Acid rain directly falls on water, but it can flow into rivers after it falls
on land. Lakes and streams become acidic (pH value goes down) when the water and the
land around it can not neutralize the acid rain. Animals that live in the water environment
are hurt and possibly killed. Some fish can only tolerate a certain amount of acid before
dying. The more acid rain that falls, the life in the bodies of water decreases.
Furthermore, animals that eat prey that is affected will be killed because they will be
consuming acid.
4.6
SOIL POLLUTION
Soil contamination is caused by the presence of man-made chemicals or other alteration
in the natural soil environment. This type of contamination typically arises from the
rupture of underground storage tanks, application of pesticides, percolation of
contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes
from landfills or direct discharge of industrial wastes to the soil. The most common
chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other
heavy metals. This occurrence of this phenomenon is correlated with the degree of
industrialization and intensity of chemical usage.
The concern over soil contamination stems primarily from health risks, both of direct
contact and from secondary contamination of water supplies. Mapping of contaminated
soil sites and the resulting cleanup are time consuming and expensive tasks, requiring
extensive amounts of geology, hydrology, chemistry and computer modeling skills.
The United States, while having some of the most widespread soil contamination, has
actually been a leader in defining and implementing standards for cleanup. Other
industrialized countries have a large number of contaminated sites, but lag the U.S. in
executing remediation. Developing countries may be leading in the next generation of
new soil contamination cases.
Each year in the U.S., thousands of sites complete soil contamination cleanup, some by
using microbes that “eat up” toxic chemicals in soil, many others by simple excavation
and others by more expensive high-tech soil vapor extraction or air stripping. At the same
time, efforts proceed worldwide in creating and identifying new sites of soil
contamination, particularly in industrial countries other than the U.S., and in developing
countries which lack the money and the technology to adequately protect soil resources.
4.6.1
Microanalysis of soil contamination
To understand the fundamental nature of soil contamination, it is necessary to envision
the variety of mechanisms for pollutants to become entrained in soil. Soil particulates
may be composed of a gamut of organic and inorganic chemicals with variations in
cation exchange capacity, buffering capacity, and redox poise. For example, at the
extremes, one has a sand component, a coarse grained, inert, and totally inorganic
substance; whereas peat soils are dominated by a fine organic material, made of
decomposing organic material and highly active. Most soils are mixtures of soil subtypes
53
and thus have quite complex characteristics. There is also a great diversity of soil
porosity, ranging from gravels to sands to silt to clay (in increasing order of porosity),
pore size, and pore tortuosity (both in decreasing order). Finally there is a wide spectrum
of chemical bonding or adhesion characteristics: each contaminant has a different
interaction or bonding mechanism with a given soil type.
On balance, some contaminants may literally drain through soils such as sand and gravel
and move to other soils or deeper aquifers, while polar or organic chemicals discharged
into a clay soil will have a very high adsorption. Thus most soil contamination is the
result of pollutants adhering to the soil particle surface, or lodging in interstices of a soil
matrix. Clearly the equilibrium reached is a dynamic one, where new pollutants may
lodge on new soil particles and the action of groundwater movement may over time
transport some of the soil contaminants to other locations or depths.
Soil contamination results when hazardous substances are either spilled or buried directly
in the soil or migrate to the soil from a spill that has occurred elsewhere. For example,
soil can become contaminated when small particles containing hazardous substances are
released from a smokestack and are deposited on the surrounding soil as they fall out of
the air. Another source of soil contamination could be water that washes contamination
from an area containing hazardous substances and deposits the contamination in the soil
as it flows over or through it.
4.6.2
Effects on human health
The major concern is that there are many sensitive land uses where people are in direct
contact with soils such as residences, parks, schools and playgrounds. Other contact
mechanisms include contamination of drinking water or inhalation of soil contaminants
which have vaporized. There is a very large set of health consequences from exposure to
soil contamination depending on pollutant type, pathway of attack and vulnerability of
the exposed population. Chromium and obsolete pesticide formulations are carcinogenic
to populations. Lead is especially hazardous to young children, in which group there is a
high risk of developmental damage to the brain,while to all populations kidney damage is
a risk.
Chronic exposure to at sufficient concentrations is known to be associated with higher
incidence of leukemia. Obsolete pesticides such as mercury and cyclodienes are known
to induce higher incidences of kidney damage, some irreversible; cyclodienes are linked
to liver toxicity. Organophosphates and carbamates can induce a chain of responses
leading to neuromuscular blockage. Many chlorinated solvents induce liver changes,
kidney changes and depression of the central nervous system. There is an entire spectrum
of further health effects such as headache, nausea, fatigue (physical), eye irritation and
skin rash for the above cited and other chemicals.
4.6.3
Effects on ecosystem
Not unexpectedly, soil contaminants can have significant deleterious consequences for
ecosystems. There are radical soil chemistry changes which can arise from the presence
of many hazardous chemicals even at low concentration of the contaminant species.
54
These changes can manifest in the alteration of metabolism of endemic microorganisms
and arthropods resident in a given soil environment. The result can be virtual eradication
of some of the primary food chain, which in turn have major consequences for predator
or consumer species. Even if the chemical effect on lower life forms is small, the lower
pyramid levels of the food chain may ingest alien chemicals, which normally become
more concentrated for each consuming rung of the food chain. Many of these effects are
now well known, such as the concentration of persistent DDT materials for avian
consumers, leading to weakening of egg shells, increased chick mortality and potentially
species extinction.
Effects occur to agricultural lands which have certain types of soil contamination.
Contaminants typically alter plant metabolism, most commonly to reduce crop yields.
This has a secondary effect upon soil conservation, since the languishing crops cannot
shield the earth's soil mantle from erosion phenomena. Some of these chemical
contaminants have long half-lives and in other cases derivative chemicals are formed
from decay of primary soil contaminants.
4.6.4
Cleanup options
Microbes can be used in soil cleanup. Cleanup or remediation is analyzed by
environmental scientists who utilize field measurement of soil chemicals and also apply
computer models for analyzing transport and fate of soil chemicals. Thousands of soil
contamination cases are currently in active cleanup across the U.S. as of 2006. There are
several principal strategies for remediation:
4.7

Excavate soil and remove it to a disposal site away from ready pathways for human
or sensitive ecosystem contact. This technique also applies to dredging of bay muds
containing toxins.

Aeration of soils at the contaminated site (with attendant risk of creating air pollution)

Bioremediation, involving microbial digestion of certain organic chemicals.
Techniques used in bioremediation include landfarming, biostimulation and
bioaugmentation soil biota with commercially available microflora.

Extraction of groundwater or soil vapor with an active electromechanical system,
with subsequent stripping of the contaminants from the extract.

Containment of the soil contaminants (such as by capping or paving over in place).
GREENHOUSE GASES
Many chemical compounds present in Earth's atmosphere behave as 'greenhouse gases'.
These are gases which allow direct sunlight (relative shortwave energy) to reach the
Earth's surface unimpeded. As the shortwave energy (that in the visible and ultraviolet
portion of the spectra) heats the surface, longer-wave (infrared) energy (heat) is reradiated to the atmosphere. Greenhouse gases absorb this energy, thereby allowing less
heat to escape back to space, and 'trapping' it in the lower atmosphere.
55
Many greenhouse gases occur naturally in the atmosphere, such as carbon dioxide,
methane, water vapor, and nitrous oxide, while others are synthetic. Those that are manmade include the chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs) and
Perfluorocarbons (PFCs), as well as sulfur hexafluoride (SF6). Atmospheric
concentrations of both the natural and man-made gases have been rising over the last few
centuries due to the industrial revolution. As the global population has increased and our
reliance on fossil fuels (such as coal, oil and natural gas) has been firmly solidified, so
emissions of these gases have risen. While gases such as carbon dioxide occur naturally
in the atmosphere, through our interference with the carbon cycle (through burning forest
lands, or mining and burning coal), we artificially move carbon from solid storage to its
gaseous state, thereby increasing atmospheric concentrations.
Greenhouse gases which reduce the loss of heat into space and therefore contribute to
global temperatures through the greenhouse effect. Greenhouse gases are essential to
maintaining the temperature of the Earth; without them the planet would be so cold as to
be uninhabitable. However, an excess of greenhouse gases can raise the temperature of a
planet to lethal levels, as on Venus where the 96.5% carbon dioxide (CO2) atmosphere
results in surface temperatures of about 467 °C (872 °F). Greenhouse gases are produced
by many natural and industrial processes, which currently result in CO2 levels of 380
ppmv (parts per million by volume) in the atmosphere.
4.7.1
Greenhouse Effect
The greenhouse effect was discovered by Joseph Fourier in 1824 and was first
investigated quantitatively by Svante Arrhenius in 1896. It is the process by which
absorption and emission of infrared radiation by atmospheric gases warm a planet's lower
atmosphere and surface.
When sunlight reaches the surface of the Earth, some of it is absorbed and warms the
surface. Because the Earth's surface is much cooler than the sun, it radiates energy at
much longer wavelengths than the sun does, peaking in the infrared at about 10 µm. The
atmosphere absorbs these longer wavelengths more effectively than it does the shorter
wavelengths from the sun. The absorption of this longwave radiant energy warms the
atmosphere; the atmosphere is also warmed by transfer of sensible and latent heat from
the surface. Greenhouse gases also emit longwave radiation both upward to space and
downward to the surface. The downward part of this longwave radiation emitted by the
atmosphere is the "greenhouse effect". The term is a misnomer though, as this process is
not the mechanism that warms greenhouses.
On earth, the most abundant greenhouse gases are, in order of relative abundance:

Water vapor, which causes about 36–70% of the greenhouse effect on Earth. (Note
clouds typically affect climate differently from other forms of atmospheric water.)

Carbon dioxide, which causes 9–26%

Methane, which causes 4–9%

Ozone, which causes 3–7%
56

Other gases nitrous oxide, CFCs, etc.
(Note that this is a combination of the strength of the greenhouse effect of the gas and its
abundance. For example, methane is a much stronger greenhouse gas than CO2, but
present in much smaller concentrations).
It is not possible to state that a certain gas causes a certain percentage of the greenhouse
effect, because the influences of the various gases are not additive. (The higher ends of
the ranges quoted are for the gas alone; the lower ends, for the gas counting overlaps.)
Other greenhouse gases include, but are not limited to, nitrous oxide, sulfur hexafluoride,
hydrofluorocarbons, perfluorocarbons and chlorofluorocarbons.
The major atmospheric constituents (nitrogen, N2 and oxygen, O2) are not greenhouse
gases. This is because homonuclear diatomic molecules such as N2 and O2 neither absorb
nor emit infrared radiation, as there is no net change in the dipole moment of these
molecules when they vibrate. Molecular vibrations occur at energies that are of the same
magnitude as the energy of the photons on infrared light. Heteronuclear diatomics such
as CO or HCl absorb IR; however, these molecules are short-lived in the atmosphere
owing to their reactivity and solubility. As a consequence they do not contribute
significantly to the greenhouse effect.
Late 19th century scientists experimentally discovered that N2 and O2 did not absorb
infrared radiation (called, at that time, "dark radiation") and that CO2 and many other
gases did absorb such radiation. It was recognized in the early 20th century that the
known major greenhouse gases in the atmosphere caused the earth's temperature to be
higher than it would have been without the greenhouse gases.
4.7.2
Greenhouse Gases : Trends And Role
1. Carbon Dioxide(CO2)
The natural production and absorption of carbon dioxide (CO2) is achieved through the
terrestrial biosphere and the ocean. However, humankind has altered the natural carbon
cycle by burning coal, oil, natural gas and wood and since the industrial revolution began
in the mid 1700s, each of these actvities has increased in scale and distribution. Carbon
dioxide was the first greenhouse gas demonstrated to be increasing in atmospheric
concentration with the first conclusive measurements being made in the last half of the
20th century. Prior to the industrial revolution, concentrations were fairly stable at 280
ppm. Today, they are around 370 ppm, an increase of well over 30 %. The atmospheric
concentration has a marked seasonal oscillation that is mostly due to the greater extent of
landmass in the northern hemisphere and its vegetation. A greater drawdown of CO2
occurs in the northern hemisphere spring and summer as plants convert CO2 to plant
material through photosynthesis. It is then released again in the fall and winter as the
plants decompose.
2. Methane (CH4)
57
Methane is an extrememly effective absorber of radiation, though its atmospheric
concentration is less than CO2 and its lifetime in the atmosphere is brief (10-12 years),
compared to some other greenhouse gases (such as CO2, N2O, CFCs). Methane(CH4) has
both natural and anthropogenic sources. It is released as part of the biological processes
in low oxygen environments, such as in swamplands or in rice production (at the roots of
the plants). Over the last 50 years, human activities such as growing rice, raising cattle,
using natural gas and mining coal have added to the atmospheric concentration of
methane. Direct atmospheric measurement of atmospheric methane has been possible
since the late 1970s and its conentration rose from 1.52 ppmv in 1978 by around 1 % per
year to 1990, since when there has been little sustained increase. The current atmospheric
concentration is ~1.77 ppmv, and there is no scientific consensus on why methane has
not risen much since around 1990.
3. Tropospheric Ozone (O3)
Ultraviolet radiation and oxygen interact to form ozone in the stratosphere. Existing in a
broad band, commonly called the 'ozone layer', a small fraction of this ozone naturally
descends to the surface of the Earth. However, during the 20th century, this tropospheric
ozone has been supplemented by ozone created by human processes. The exhaust
emissions from automobiles and pollution from factories (as well as burning vegetation)
leads to greater concentrations of carbon and nitrogen molecules in the lower atmosphere
which, when it they are acted on by sunlight, produce ozone. Consequently, ozone has
higher concentrations in and around cities than in sparsely populated areas, though there
is some transport of ozone downwind of major urban areas. Ozone is an important
contributor to photochemical smog. Concentrations of ozone have risen by around 30%
since the pre-industrial era, and is now considered by the IPCC to be the third most
important greenhouse gas after carbon dioxide and methane. An additional complication
of ozone is that it also interacts with and is modulated by concentrations of methane.
4. Nitrous Oxide
Concentrations of nitrous oxide also began to rise at the beginning of the industrial
revolution and is understood to be produced by microbial processes in soil and water,
including those reactions which occur in fertilizer containing nitrogen. Increasing use of
these fertilizers has been made over the last century. Global concentration for N2O in
1998 was 314 ppb, and in addition to agricultural sources for the gas, some industrial
processes (fossil fuel-fired power plants, nylon production, nitric acid production and
vehicle emissions) also contribute to its atmospheric load.
5. CFCs etc.
CFCs (chlorofluorocarbons) have no natural source, but were entirely synthesized for
such diverse uses as refrigerants, aerosol propellants and cleaning solvents. Their
creation was in 1928 and since then concentrations of CFCs in the atmosphere have been
rising. Due to the discovery that they are able to destroy stratospheric ozone, a global
effort to halt their production was undertaken and was extremely successful. So much so
that levels of the major CFCs are now remaining level or declining. However, their long
atmospheric lifetimes determine that some concentration of the CFCs will remain in the
58
atmosphere for over 100 years. Since they are also greenhouse gas, along with such other
long-lived synthesized gases as CF4 (carbontatrafluoride), SF6 (sulfurhexafluoride), they
are of concern. Another set of synthesized compounds called HFCs (hydrofluorcarbons)
are also greenhouse gases, though they are less stable in the atmosphere and therefore
have a shorter lifetime and less of an impact as a greenhouse gas.
6. Carbon Monoxide (CO) and other reactive gases
Carbon monoxide (CO) is not considered a direct greenhouse gas, mostly because it does
not absorb terrestrial thermal IR energy strongly enough. However, CO is able to
modulate the production of methane and tropospheric ozone. The Northern Hemisphere
contains about twice as much CO as the Southern Hemisphere because as much as half of
the global burden of CO is derived from human activity, which is predominantly located
in the NH. Due to the spatial variability of CO, it is difficult to ascertain global
concentrations, however, it appears as though they were generally increasing until the
late 1980s, and have since begun to decline somewhat. One possible explanation is the
reduction in vehicle emissions of CO since greater use of catalytic converters has been
made.
Volatile Organic Compounds (VOCs) also have a small direct impact as greenhouse
gases, as well being involved in chemical processes which modulate ozone production.
VOCs include non-methane hydrocarbons (NMHC), and oxygenated NMHCs (eg.
alcohols and organic acids), and their largest source is natural emissions from vegetation.
However, there are some anthropogenic sources such as vehicle emissions, fuel
production and biomass burning. Though measurement of VOCs is extremely difficult, it
is expected that most anthropogenic emissions of these compounds have increased in
recent decades.
4.7.3
Sources of the Greenhouse Gases
Natural and anthropogenic
Most greenhouse gases have both natural and anthropogenic sources. During the preindustrial holocene, concentrations of these gases were roughly constant. Since the
industrial revolution, concentrations of all the long-lived greenhouse gases have
increased due to human actions.
Gas
Preindustri
al Level
CO2
280 ppm
CH4
N2O
CFC-12
Increase
since 1750
Radiative
forcing
(W/m2)
384ppm
104 ppm
1.46
700 ppb
1,745 ppb
1,045 ppb
0.48
270 ppb
314 ppb
44 ppb
0.15
533 ppt
533 ppt
0.17
0
Current
Level
59
Ice cores provide evidence for variation in greenhouse gas concentrations over the past
800,000 years. Both CO2 and CH4 vary between glacial and interglacial phases, and
concentrations of these gases correlate strongly with temperature. Before the ice core
record, direct measurements do not exist. Various proxies and modelling suggests large
variations; 500 Myr ago CO2 levels were likely 10 times higher than now. Indeed higher
CO2 concentrations are thought to have prevailed throughout most of the Phanerozoic
ion, with concentrations four to six times current concentrations during the Mesozoic era,
and ten to fifteen times current concentrations during the early Palaeozoic era until the
middle of the Devonian period, about 400 Mya. The spread of land plants is thought to
have reduced CO2 concentrations during the late Devonian, and plant activities as both
sources and sinks of CO2 have since been important in providing stabilising feedbacks.
Earlier still, a 200-million year period of intermittent, widespread glaciation extending
close to the equator (Snowball Earth) appears to have been ended suddenly, about 550
Mya, by a colossal volcanic outgassing which raised the CO2 concentration of the
atmosphere abruptly to 12%, about 350 times modern levels, causing extreme greenhouse
conditions and carbonate deposition as limestone at the rate of about 1mm per day. This
episode marked the close of the Precambrian eon, and was succeeded by the generally
warmer conditions of the Phanerozoic, during which multicellular animal and plant life
evolved. No volcanic carbon dioxide emission of comparable scale has occurred since. In
the modern era, emissions to the atmosphere from volcanoes are only about 1% of
emissions from human sources
Anthropogenic greenhouse gases
Since about 1750 human activity has increased the concentration of carbon dioxide and
of some other important greenhouse gases. Natural sources of carbon dioxide are more
than 20 times greater than sources due to human activity, but over periods longer than a
few years natural sources are closely balanced by natural sinks such as weathering of
continental rocks and photosynthesis of carbon compounds by plants and marine
plankton. As a result of this balance, the atmospheric concentration of carbon dioxide
remained between 260 and 280 parts per million for the 10,000 years between the end of
the last glacial maximum and the start of the industrial era.
Some of the main sources of greenhouse gases due to human activity include:

burning of fossil fuels and deforestation leading to higher carbon dioxide
concentrations. Land use change (mainly deforestation in the tropics) account for up
to one third of total anthropogenic CO2 emissions.

livestock enteric fermentation and manure management, paddy rice farming, land use
and wetland changes, pipeline losses, and covered vented landfill emissions leading
to higher methane atmospheric concentrations. Many of the newer style fully vented
septic systems that enhance and target the fermentation process also are sources of
atmospheric methane.

use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and
halons in fire suppression systems and manufacturing processes.

agricultural activities, including the use of fertilizers, that lead to higher nitrous oxide
concentrations.
60
The seven sources of CO2 from fossil fuel combustion are (with percentage contributions
for 2000–2004):
2. Solid fuels (e.g. coal): 35%
3. Liquid fuels (e.g. gasoline): 36%
4. Gaseous fuels (e.g. natural gas): 20%
5. Flaring gas industrially and at wells: <1%
6. Cement production: 3%
7. Non-fuel hydrocarbons: <1%
8. The "international bunkers" of shipping and air transport not included in national
inventories: 4%
The USEPA (United State Envvironment Protection Agency) ranks the major greenhouse
gas contributing end-user sectors in the following order: industrial, transportation,
residential, commercial and agricultural. Major sources of an individual's greenhouse
gases include home heating and cooling, electricity consumption, and transportation.
Corresponding conservation measures are improving home building insulation, compact
fluorescent lamps and choosing energy-efficient vehicles.
Carbon dioxide, methane, nitrous oxide and three groups of fluorinated gases (sulfur
hexafluoride, HFCs, and PFCs) are the major greenhouse gases and the subject of the
Kyoto Protocol, which came into force in 2005.
Although CFCs are greenhouse gases, they are regulated by the Montreal Protocol, which
was motivated by CFCs' contribution to ozone depletion rather than by their contribution
to global warming.
4.7.4
Greenhouse Gas Emissions
Measurements from Antarctic ice cores show that just before industrial emissions started,
atmospheric CO2 levels were about 280 parts per million by volume (ppm; the units µL/L
are occasionally used and are identical to parts per million by volume). From the same
ice cores it appears that CO2 concentrations stayed between 260 and 280 ppm during the
preceding 10,000 years. Studies using evidence from stomata of fossilized leaves suggest
greater variability, with CO2 levels above 300 ppm during the period 7,000–10,000 years
ago, though others have argued that these findings more likely reflect calibration/
contamination problems rather than actual CO2 variability.
Since the beginning of the Industrial Revolution, the concentrations of many of the
greenhouse gases have increased. The concentration of CO2 has increased by about 100
ppm (i.e., from 280 ppm to 380 ppm). The first 50 ppm increase took place in about 200
years, from the start of the Industrial Revolution to around 1973; the next 50 ppm
increase took place in about 33 years, from 1973 to 2006. The greenhouse gases with the
largest radiative forcing are:
61
Relevant to radiative forcing
Gas
Current (1998)
Amount by volume
CO2
365 ppm {383 ppm
(2007.01)}
1,745 ppb
314 ppb
CH4
N2O
Increase over
pre-industrial
(1750)
87 ppm {105
ppm (2007.01)}
1,045 ppb
44 ppb
Percentage
increase
31% {37.77 %
(2007.01)}
150%
16%
Radiative
forcing
(W/m²)
1.46 {~1.532
(2007.01)}
0.48
0.15
(Source: IPCC radiative forcing report 1994 updated (to 1998 & 2003) by IPCC TAR
table 6.1).
Recent rates of change and emission
The sharp acceleration in CO2 emissions since 2000 of >3% y−1 (>2 ppm y−1) from 1.1%
y−1 during the 1990s is attributable to the lapse of formerly declining trends in carbon
intensity of both developing and developed nations. Although over 3/4 of cumulative
anthropogenic CO2 is still attributable to the developed world, China was responsible for
most of global growth in emissions during this period. Localised plummeting emissions
associated with the collapse of the Soviet Union have been followed by slow emissions
growth in this region due to more efficient energy use, made necessary by the increasing
proportion of it that is exported. In comparison, methane has not increased appreciably,
and N2O by 0.25% y−1.
4.7.5
Role of Greenhouse Gases on Climate Change
Given the natural variability of the Earth’s climate, it is difficult to determine the extent
of change that humans cause. In computer-based models, rising concentrations of
greenhouse gases generally produce an increase in the average temperature of the Earth.
Rising temperatures may, in turn, produce changes in weather, sea levels, and land use
patterns, commonly referred to as “climate change.”
Assessments generally suggest that the Earth’s climate has warmed over the past century
and that human activity affecting the atmosphere is likely an important driving factor. A
National Research Council study dated May 2001 stated, “Greenhouse gases are
accumulating in Earth’s atmosphere as a result of human activities, causing surface air
temperatures and sub-surface ocean temperatures to rise. Temperatures are, in fact,
rising. The changes observed over the last several decades are likely mostly due to
human activities, but we cannot rule out that some significant part of these changes is
also a reflection of natural variability.”
However, there is uncertainty in how the climate system varies naturally and reacts to
emissions of greenhouse gases. Making progress in reducing uncertainties in projections
of future climate will require better awareness and understanding of the buildup of
greenhouse gases in the atmosphere and the behavior of the climate system.
62
4.8
OZONE LAYER AND OZONE HOLE
The ozone layer is a layer in Earth's atmosphere which contains relatively high
concentrations of ozone (O3). This layer absorbs 93-99% of the sun's high frequency
ultraviolet light, which is potentially damaging to life on earth. Over 91% of ozone in
earth's atmosphere is present here. "Relatively high" means a few parts per million—
much higher than the concentrations in the lower atmosphere but still small compared to
the main components of the atmosphere. It is mainly located in the lower portion of the
stratosphere from approximately 15 km to 35 km above Earth's surface, though the
thickness varies seasonally and geographically.
The ozone layer was discovered in 1913 by the French physicists Charles Fabry and
Henri Buisson. Its properties were explored in detail by the British meteorologist G. M.
B. Dobson, who developed a simple spectrophotometer that could be used to measure
stratospheric ozone from the ground. Between 1928 and 1958 Dobson established a
worldwide network of ozone monitoring stations which continues to operate today
(2008). The "Dobson unit", a convenient measure of the total amount of ozone in a
column overhead, is named in his honor.
4.8.1
Origin of ozone or Ozone Cycle
The photochemical mechanisms that give rise to the ozone layer were worked out by the
British physicist Sidney Chapman in 1930. Ozone in the earth's stratosphere is created by
ultraviolet light (whose wavelength is shorter than 240 nm) striking oxygen molecules
containing two oxygen atoms (O2), splitting them into individual oxygen atoms (atomic
oxygen); the atomic oxygen then combines with unbroken O2 to create ozone, O3. The
ozone molecule is also unstable (although, in the stratosphere, long-lived) and when
ultraviolet light between 310 and 200 nm hits ozone it splits into a molecule of O 2 and an
atom of atomic oxygen, a continuing process called the ozone-oxygen cycle, thus
creating an ozone layer in the stratosphere, the region from about 10 to 50 km (32,000 to
164,000 feet) above Earth's surface. About 90% of the ozone in our atmosphere is
contained in the stratosphere. Ozone concentrations are greatest between about 20 and 40
km, where they range from about 2 to 8 parts per million. If all of the ozone were
compressed to the pressure of the air at sea level, it would be only a few millimeters
thick.
Ten percent of the ozone in the atmosphere is contained in the troposphere, the lowest
part of our atmosphere where all of our weather takes place. Tropospheric ozone has two
sources: about 10 % is transported down from the stratosphere while the remainder is
created in smaller amounts through different mechanisms.
4.8.2
Distribution of ozone in the stratosphere
63
The thickness of the ozone layer—that is, the total amount of ozone in a column
overhead—varies by a large factor worldwide, being in general smaller near the equator
and larger as one moves towards the poles. It also varies with season, being in general
thicker during the spring and thinner during the autumn. The reasons for this latitude and
seasonal dependence are complicated, involving atmospheric circulation patterns as well
as solar intensity.
Since stratospheric ozone is produced by solar UV radiation, one might expect to find the
highest ozone levels over the tropics and the lowest over polar regions. The same
argument would lead one to expect the highest ozone levels in the summer and the lowest
in the winter. The observed behavior is very different: most of the ozone is found in the
mid-to-high latitudes of the northern and southern hemispheres, and the highest levels are
found in the spring, not summer, and the lowest in the autumn, not winter. During winter,
the ozone layer actually increases in depth. This puzzle is explained by the prevailing
stratospheric wind patterns, known as the Brewer-Dobson circulation. While most of the
ozone is indeed created over the tropics, the stratospheric circulation then transports it
poleward and downward to the lower stratosphere of the high latitudes.
The ozone layer is higher in altitude in the tropics, and lower in altitude in the
extratropics, especially in the polar regions. This altitude variation of ozone results from
the slow circulation that lifts the ozone-poor air out of the troposphere into the
stratosphere. As this air slowly rises in the tropics, ozone is produced by the overhead
sun which photolyzes oxygen molecules. As this slow circulation bends towards the midlatitudes, it carries the ozone-rich air from the tropical middle stratosphere to the midand-high latitudes lower stratosphere. The high ozone concentrations at high latitudes are
due to the accumulation of ozone at lower altitudes.
4.8.3
Importance of ozone layer
Although the concentration of the ozone in the ozone layer is very small, it is vitally
important to life because it absorbs biologically harmful ultraviolet (UV) radiation
emitted from the Sun. UV radiation is divided into three categories, based on its
wavelength; these are referred to as UV-A, UV-B, and UV-C. UV-C, which would be
very harmful to humans, is entirely screened out by ozone at around 35 km altitude. UVB radiation can be harmful to the skin and is the main cause of sunburn; excessive
exposure can also cause genetic damage, as a result problems such as skin cancer. The
ozone layer is very effective at screening out UV-B; for radiation with a wavelength of
290 nm, the intensity at Earth's surface is 350 billion times weaker than at the top of the
atmosphere. Nevertheless, some UV-B reaches the surface. Most UV-A reaches the
surface; this radiation is significantly less harmful, although it can potentially cause
genetic damage.
Depletion of the ozone layer allows more of the UV radiation, and particularly the more
harmful wavelengths, to reach the surface, causing increased genetic damage to living
creatures and organisms.
4.8.4
Regulation
64
On January 23, 1978, Sweden became the first nation to ban CFC-containing aerosol
sprays that are thought to damage the ozone layer. A few other countries, including the
United States, Canada, and Norway, followed suit later that year, but the European
Community rejected an analogous proposal. Even in the U.S., chlorofluorocarbons
continued to be used in other applications, such as refrigeration and industrial cleaning,
until after the discovery of the Antarctic ozone hole in 1985. After negotiation of an
international treaty (the Montreal Protocol), CFC production was sharply limited
beginning in 1987 and phased out completely by 1996.
On August 2, 2003, scientists announced that the depletion of the ozone layer may be
slowing down due to the international ban on CFCs. Three satellites and three ground
stations confirmed that the upper atmosphere ozone depletion rate has slowed down
significantly during the past decade. The study was organized by the American
Geophysical Union. Some breakdown can be expected to continue due to CFCs used by
nations which have not banned them, and due to gases which are already in the
stratosphere. CFCs have very long atmospheric lifetimes, ranging from 50 to over 100
years, so the final recovery of the ozone layer is expected to require several lifetimes.
Compounds containing C–H bonds are being designed to replace the function of CFC's
(such as HCFC), since these compounds are more reactive and less likely to survive long
enough in the atmosphere to reach the stratosphere where they could affect the ozone
layer.
4.9
OZONE HOLE AND OZONE DEPLETION
Ozone depletion describes two distinct, but related observations: a slow, steady decline
of about 4 percent per decade in the total amount of ozone in Earth's stratosphere since
the late 1970s; and a much larger, but seasonal, decrease in stratospheric ozone over
Earth's polar regions during the same period. The latter phenomenon is commonly
referred to as the ozone hole. In addition to this well-known stratospheric ozone
depletion, there are also tropospheric ozone depletion events, which occur near the
surface in polar regions during spring. Ozone levels, over the northern hemisphere, have
been dropping by 4% per decade. Over approximately 5% of the Earth's surface, around
the north and south poles, much larger (but seasonal) declines have been seen; these are
the ozone holes.
4.9.1
Ozone depletion mechanism
Ozone can be destroyed by a number of free radical catalysts, the most important of
which are the hydroxyl radical (OH·), the nitric oxide radical (NO·) and atomic chlorine
(Cl·) and bromine (Br·). All of these have both natural and anthropogenic (manmade)
sources; at the present time, most of the OH· and NO· in the stratosphere is of natural
origin, but human activity has dramatically increased the high in oxygen chlorine and
bromine. These elements are found in certain stable organic compounds, especially
chlorofluorocarbons (CFCs), which may find their way to the stratosphere without being
destroyed in the troposphere due to their low reactivity. Once in the stratosphere, the Cl
65
and Br atoms are liberated from the parent compounds by the action of ultraviolet light
e.g.
CFCl3 + hν → CFCl2 + Cl
Where 'h' is Planck's constant, 'ν' is frequency of electromagnetic radiation.
The Cl and Br atoms can then destroy ozone molecules through a variety of catalytic
cycles. In the simplest example of such a cycle, a chlorine atom reacts with an ozone
molecule, taking an oxygen atom with it (forming ClO) and leaving a normal oxygen
molecule. A free oxygen atom then takes away the oxygen from the ClO, and the final
result is an oxygen molecule and a chlorine atom, which then reinitiates the cycle. The
chemical shorthand for these gas-phase reactions is:
Cl + O3 → ClO + O2
ClO + O → Cl + O2
The net reaction is : O3 + O → 2 O2, the "recombination" reaction given above.
The overall effect is to increase the rate of recombination, leading to an overall decrease
in the amount of ozone. For this particular mechanism to operate there must be a source
of O atoms, which is primarily the photo dissociation of O3; thus this mechanism is only
important in the upper stratosphere where such atoms are abundant. More complicated
mechanisms have been discovered that lead to ozone destruction in the lower
stratosphere as well.
A single chlorine atom would keep on destroying ozone for up to two years (the time
scale for transport back down to the troposphere) were it not for reactions that remove
them from this cycle by forming reservoir species such as hydrogen chloride (HCl) and
chlorine nitrate (ClONO2). On a per atom basis, bromine is even more efficient than
chlorine at destroying ozone, but there is much less bromine in the atmosphere at present.
As a result, both chlorine and bromine contribute significantly to the overall ozone
depletion. Laboratory studies have shown that fluorine and iodine atoms participate in
analogous catalytic cycles. However, in the Earth's stratosphere, fluorine atoms react
rapidly with water and methane to form strongly-bound HF, while organic molecules
which contain iodine react so rapidly in the lower atmosphere that they do not reach the
stratosphere in significant quantities. Furthermore, a single chlorine atom is able to react
with 100,000 ozone molecules. This fact plus the amount of chlorine released into the
atmosphere by chlorofluorocarbons (CFCs) yearly demonstrates how dangerous CFCs
are to the environment.
4.9.2
Consequences of ozone layer depletion
Since the ozone layer absorbs UV-B ultraviolet light from the Sun, ozone layer depletion
is expected to increase surface UV-B levels, which could lead to damage, including
increases in skin cancer. This was the reason for the Montreal Protocol. Although
decreases in stratospheric ozone are well-tied to CFCs and there are good theoretical
66
reasons to believe that decreases in ozone will lead to increases in surface UV-B, there is
no direct observational evidence linking ozone depletion to higher incidence of skin
cancer in human beings. This is partly due to the fact that UV-A, which has also been
implicated in some forms of skin cancer, is not absorbed by ozone, and it is nearly
impossible to control statistics for lifestyle changes in the populace.
Increased UV
Ozone, while a minority constituent in the earth's atmosphere, is responsible for most of
the absorption of UV-B radiation. The amount of UV-B radiation that penetrates through
the ozone layer decreases exponentially with the slant-path thickness/ density of the
layer. Correspondingly, a decrease in atmospheric ozone is expected to give rise to
significantly increased levels of UV-B near the surface.
Biological effects of increased UV and microwave radiation from a depleted
ozone layer
The main public concern regarding the ozone hole has been the effects of surface UV on
human health. So far, ozone depletion in most locations has been typically a few percent
and, as noted above, no direct evidence of health damage is available in most latitudes.
Were the high levels of depletion seen in the ozone hole ever to be common across the
globe, the effects could be substantially more dramatic. As the ozone hole over
Antarctica has in some instances grown so large as to reach southern parts of Australia
and New Zealand, environmentalists have been concerned that the increase in surface UV
could be significant.
Effects of ozone layer depletion on Humans
UV-B (the higher energy UV radiation absorbed by ozone) is generally accepted to be a
contributory factor to skin cancer. In addition, increased surface UV leads to increased
tropospheric ozone, which is a health risk to humans. The increased surface UV also
represents an increase in the vitamin D synthetic capacity of the sunlight.
The cancer preventive effects of vitamin D represent a possible beneficial effect of ozone
depletion. In terms of health costs, the possible benefits of increased UV irradiance may
outweigh the burden.
1. Basal and Squamous Cell Carcinomas -- The most common forms of skin cancer in
humans, basal and squamous cell carcinomas, have been strongly linked to UV-B
exposure. The mechanism by which UV-B induces these cancers is well understood —
absorption of UV-B radiation causes the pyrimidine bases in the DNA molecule to form
dimers, resulting in transcription errors when the DNA replicates. These cancers are
relatively mild and rarely fatal, although the treatment of squamous cell carcinoma
sometimes requires extensive reconstructive surgery. By combining epidemiological data
with results of animal studies, scientists have estimated that a one percent decrease in
stratospheric ozone would increase the incidence of these cancers by 2%.
67
2. Malignant Melanoma -- Another form of skin cancer, malignant melanoma, is much
less common but far more dangerous, being lethal in about 15% - 20% of the cases
diagnosed. The relationship between malignant melanoma and ultraviolet exposure is not
yet well understood, but it appears that both UV-B and UV-A are involved. Experiments
on fish suggest that 90 to 95% of malignant melanomas may be due to UV-A and visible
radiation whereas experiments on opossums suggest a larger role for UV-B. Because of
this uncertainty, it is difficult to estimate the impact of ozone depletion on melanoma
incidence. One study showed that a 10% increase in UV-B radiation was associated with
a 19% increase in melanomas for men and 16% for women. A study of people in Punta
Arenas, at the southern tip of Chile, showed a 56% increase in melanoma and a 46%
increase in nonmelanoma skin cancer over a period of seven years, along with decreased
ozone and increased UV-B levels.
3. Cortical Cataracts -- Studies are suggestive of an association between ocular cortical
cataracts and UV-B exposure, using crude approximations of exposure and various
cataract assessment techniques. A detailed assessment of ocular exposure to UV-B was
carried out in a study on Chesapeake Bay Watermen, where increases in average annual
ocular exposure were associated with increasing risk of cortical opacity. In this highly
exposed group of predominantly white males, the evidence linking cortical opacities to
sunlight exposure was the strongest to date. However, subsequent data from a
population-based study in Beaver Dam, WI suggested the risk may be confined to men.
In the Beaver Dam study, the exposures among women were lower than exposures
among men, and no association was seen. Moreover, there were no data linking sunlight
exposure to risk of cataract in African Americans, although other eye diseases have
different prevalences among the different racial groups, and cortical opacity appears to be
higher in African Americans compared with whites.
4. Increased Tropospheric Ozone -- Increased surface UV leads to increased
tropospheric ozone. Ground-level ozone is generally recognized to be a health risk, as
ozone is toxic due to its strong oxidant properties. At this time, ozone at ground level is
produced mainly by the action of UV radiation on combustion gases from vehicle
exhausts.
Effects on Crops
An increase of UV radiation would be expected to affect crops. A number of
economically important species of plants, such as rice, depend on cyanobacteria residing
on their roots for the retention of nitrogen. Cyanobacteria are sensitive to UV light and
they would be affected by its increase.
Effects on Plankton
Research has shown a widespread extinction of plankton two million years ago that
coincided with a nearby supernova. There is a difference in the orientation and motility
of planktons when excess of UV rays reach earth. Researchers speculate that the
extinction was caused by a significant weakening of the ozone layer at that time when the
radiation from the supernova produced nitrogen oxides that catalyzed the destruction of
68
ozone (plankton are particularly susceptible to effects of UV light, and are vitally
important to marine food webs).
4.9.3
Ozone depletion and global warming
Although they are often interlinked in the mass media, the connection between global
warming and ozone depletion is not strong. There are four areas of linkage:

The same CO2 radiative forcing that produces near-surface global warming is
expected to cool the stratosphere. This cooling, in turn, is expected to produce a
relative increase in polar ozone (O3) depletion and the frequency of ozone holes.

Conversely, ozone depletion represents a radiative forcing of the climate system.
There are two opposing effects: Reduced ozone causes the stratosphere to absorb less
solar radiation, thus cooling the stratosphere while warming the troposphere; the
resulting colder stratosphere emits less long-wave radiation downward, thus cooling
the troposphere. Overall, the cooling dominates; the IPCC concludes that "observed
stratospheric O3 losses over the past two decades have caused a negative forcing of
the surface-troposphere system" of about −0.15 ± 0.10 watts per square meter
(W/m²).

One of the strongest predictions of the greenhouse effect is that the stratosphere will
cool. Although this cooling has been observed, it is not trivial to separate the effects
of changes in the concentration of greenhouse gases and ozone depletion since both
will lead to cooling. However, this can be done by numerical stratospheric modeling.
Results from the National Oceanic and Atmospheric Administration's Geophysical
Fluid Dynamics Laboratory show that above 20 km (12.4 miles), the greenhouse
gases dominate the cooling.

Ozone depleting chemicals are also greenhouse gases. The increases in concentrations
of these chemicals have produced 0.34 ± 0.03 W/m² of radiative forcing,
corresponding to about 14% of the total radiative forcing from increases in the
concentrations of well-mixed greenhouse gases.
World Ozone Day
In 1994, the United Nations General Assembly voted to designate September 16 as
"World Ozone Day", to commemorate the signing of the Montreal Protocol on that date
in 1987.
4.10
GLOBAL WARMING
Global warming is the increase in the average temperature of the Earth's near-surface air
and oceans since the mid-twentieth century, and its projected continuation.
The average global air temperature near the Earth's surface increased 0.74 ± 0.18 °C
(1.33 ± 0.32 °F) during the hundred years ending in 2005. The Intergovernmental Panel
on Climate Change (IPCC) concludes "most of the observed increase in globally
averaged temperatures since the mid-twentieth century is very likely due to the observed
69
increase in anthropogenic (man-made) greenhouse gas concentrations" via an enhanced
greenhouse effect. Natural phenomena such as solar variation combined with volcanoes
probably had a small warming effect from pre-industrial times to 1950 and a small
cooling effect from 1950 onward.
These basic conclusions have been endorsed by at least thirty scientific societies and
academies of science, including all of the national academies of science of the major
industrialized countries.
Climate model projections summarized by the IPCC indicate that average global surface
temperature will likely rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the twenty-first
century. This range of values results from the use of differing scenarios of future
greenhouse gas emissions as well as models with differing climate sensitivity.
Increasing global temperature will cause sea level to rise, and is expected to increase the
intensity of extreme weather events and to change the amount and pattern of
precipitation. Other effects of global warming include changes in agricultural yields,
trade routes, glacier retreat, species extinctions and increases in the ranges of disease
vectors.
Remaining scientific uncertainties include the amount of warming expected in the future,
and how warming and related changes will vary from region to region around the globe.
Most national governments have signed and ratified the Kyoto Protocol aimed at
reducing greenhouse gas emissions, but there is ongoing political and public debate
worldwide regarding what, if any, action should be taken to reduce or reverse future
warming or to adapt to its expected consequences.
4.10.1
Terminology
The term "global warming" refers to the warming in recent decades and its projected
continuation, and implies a human influence. The United Nations Framework
Convention on Climate Change (UNFCCC) uses the term "climate change" for humancaused change, and "climate variability" for other changes. The term "anthropogenic
global warming" (AGW) is sometimes used when focusing on human-induced changes.
4.10.2
Recent Temperature changes
Global temperatures on both land and sea have increased by 0.75 °C (1.35 °F) relative to
the period 1860–1900, according to the instrumental temperature record. This measured
temperature increase is not significantly affected by the urban heat island effect. Since
1979, land temperatures have increased about twice as fast as ocean temperatures
(0.25 °C per decade against 0.13 °C per decade). Temperatures in the lower troposphere
have increased between 0.12 and 0.22 °C (0.22 and 0.4 °F) per decade since 1979,
according to satellite temperature measurements. Temperature is believed to have been
relatively stable over the one or two thousand years before 1850, with possibly regional
fluctuations such as the Medieval Warm Period or the Little Ice Age.
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Sea temperatures increase more slowly than those on land both because of the larger
effective heat capacity of the oceans and because the ocean can lose heat by evaporation
more readily than the land. The Northern Hemisphere has more land than the Southern
Hemisphere, so it warms faster. The Northern Hemisphere also has extensive areas of
seasonal snow and sea-ice cover subject to the ice-albedo feedback. More greenhouse
gases are emitted in the Northern than Southern Hemisphere, but this does not contribute
to the difference in warming because the major greenhouse gases persist long enough to
mix between hemispheres.
4.10.3
Causes of Global Warming
The Earth's climate changes in response to external forcing, including variations in its
orbit around the Sun (orbital forcing), changes in solar luminosity, volcanic eruptions,
and atmospheric greenhouse gas concentrations. The detailed causes of the recent
warming remain an active field of research, but the scientific consensus is that the
increase in atmospheric greenhouse gases due to human activity caused most of the
warming observed since the start of the industrial era. This attribution is clearest for the
most recent 50 years, for which the most detailed data are available. Some other
hypotheses departing from the consensus view have been suggested to explain most of
the temperature increase. One such hypothesis proposes that warming may be the result
of variations in solar activity.
None of the effects of forcing are instantaneous. The thermal inertia of the Earth's oceans
and slow responses of other indirect effects mean that the Earth's current climate is not in
equilibrium with the forcing imposed. Climate commitment studies indicate that even if
greenhouse gases were stabilized at 2000 levels, a further warming of about 0.5 °C
(0.9 °F) would still occur.
4.10.4
Feedbacks
The effects of forcing agents on the climate are complicated by various feedback
processes.
One of the most pronounced feedback effects relates to the evaporation of water.
Warming by the addition of long-lived greenhouse gases such as CO2 will cause more
water to evaporate into the atmosphere. Since water vapor itself acts as a greenhouse gas,
the atmosphere warms further; this warming causes more water vapor to evaporate (a
positive feedback), and so on until other processes stop the feedback loop. The result is a
much larger greenhouse effect than that due to CO2 alone. Although this feedback
process causes an increase in the absolute moisture content of the air, the relative
humidity stays nearly constant or even decreases slightly because the air is warmer. This
feedback effect can only be reversed slowly as CO2 has a long average atmospheric
lifetime.
Feedback effects due to clouds are an area of ongoing research. Seen from below, clouds
emit infrared radiation back to the surface, and so exert a warming effect; seen from
above, clouds reflect sunlight and emit infrared radiation to space, and so exert a cooling
effect. Whether the net effect is warming or cooling depends on details such as the type
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and altitude of the cloud. These details are difficult to represent in climate models, in part
because clouds are much smaller than the spacing between points on the computational
grids of climate models. Nevertheless, cloud feedback is second only to water vapor
feedback and is positive in all the models that were used in the IPCC Fourth Assessment
Report.
A subtler feedback process relates to changes in the lapse rate as the atmosphere warms.
The atmosphere's temperature decreases with height in the troposphere. Since emission
of infrared radiation varies with the fourth power of temperature, longwave radiation
emitted from the upper atmosphere is less than that emitted from the lower atmosphere.
Most of the radiation emitted from the upper atmosphere escapes to space, while most of
the radiation emitted from the lower atmosphere is re-absorbed by the surface or the
atmosphere. Thus, the strength of the greenhouse effect depends on the atmosphere's rate
of temperature decrease with height: if the rate of temperature decrease is greater the
greenhouse effect will be stronger, and if the rate of temperature decrease is smaller then
the greenhouse effect will be weaker. Both theory and climate models indicate that
warming will reduce the decrease of temperature with height, producing a negative lapse
rate feedback that weakens the greenhouse effect. Measurements of the rate of
temperature change with height are very sensitive to small errors in observations, making
it difficult to establish whether the models agree with observations.
Another important feedback process is ice-albedo feedback. When global temperatures
increase, ice near the poles melts at an increasing rate. As the ice melts, land or open
water takes its place. Both land and open water are on average less reflective than ice,
and thus absorb more solar radiation. This causes more warming, which in turn causes
more melting, and this cycle continues.
Positive feedback due to release of CO2 and CH4 from thawing permafrost, such as the
frozen peat bogs in Siberia, is an additional mechanism that could contribute to warming.
Similarly a massive release of CH4 from methane clathrates in the ocean could cause
rapid warming, according to the clathrate gun hypothesis.
The ocean's ability to sequester carbon is expected to decline as it warms. This is because
the resulting low nutrient levels of the mesopelagic zone (about 200 to 1000 m depth)
limits the growth of diatoms in favor of smaller phytoplankton that are poorer biological
pumps of carbon.
4.10.5
Attributed and expected effects
According to United Nations Environment Programme (UNEP), economic sectors likely
to face difficulties related to climate change include banks, agriculture, transport and
others. Developing countries dependent upon agriculture will be particularly harmed by
global warming.
Although it is difficult to connect specific weather events to global warming, an increase
in global temperatures may in turn cause broader changes, including glacial retreat,
Arctic shrinkage, and worldwide sea level rise. Changes in the amount and pattern of
precipitation may result in flooding and drought. There may also be changes in the
72
frequency and intensity of extreme weather events. Other effects may include changes in
agricultural yields, addition of new trade routes, reduced summer streamflows, species
extinctions, and increases in the range of disease vectors.
Some effects on both the natural environment and human life are, at least in part, already
being attributed to global warming. A 2001 report by the IPCC suggests that glacier
retreat, ice shelf disruption such as that of the Larsen Ice Shelf, sea level rise, changes in
rainfall patterns, and increased intensity and frequency of extreme weather events, are
being attributed in part to global warming. While changes are expected for overall
patterns, intensity, and frequencies, it is difficult to attribute specific events to global
warming. Other expected effects include water scarcity in some regions and increased
precipitation in others, changes in mountain snowpack, and adverse health effects from
warmer temperatures.
Increasing deaths, displacements, and economic losses projected due to extreme weather
attributed to global warming may be exacerbated by growing population densities in
affected areas, although temperate regions are projected to experience some benefits,
such as fewer deaths due to cold exposure. A summary of probable effects and recent
understanding can be found in the report made for the IPCC Third Assessment Report by
Working Group II. The newer IPCC Fourth Assessment Report summary reports that
there is observational evidence for an increase in intense tropical cyclone activity in the
North Atlantic Ocean since about 1970, in correlation with the increase in sea surface
temperature, but that the detection of long-term trends is complicated by the quality of
records prior to routine satellite observations. The summary also states that there is no
clear trend in the annual worldwide number of tropical cyclones.
Additional anticipated effects include sea level rise of 110 to 770 millimeters (0.36 to
2.5 ft) between 1990 and 2100, repercussions to agriculture, possible slowing of the
thermohaline circulation, reductions in the ozone layer, increased intensity (but less
frequent) of hurricanes and extreme weather events, lowering of ocean pH, and the
spread of diseases such as malaria and dengue fever. One study predicts 18% to 35% of a
sample of 1,103 animal and plant species would be extinct by 2050, based on future
climate projections. However, few mechanistic studies have documented extinctions due
to recent climate change and one study suggests that projected rates of extinction are
uncertain.
4.11
ULTRAVIOLET
Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of
visible light, but longer than soft X-rays. It is so named because the spectrum consists of
electromagnetic waves with frequencies higher than those that humans identify as the
colour violet.
UV light is typically found as part of the radiation received by the Earth from the Sun.
Most humans are aware of the effects of UV through the painful condition of sunburn.
The UV spectrum has many other effects, including both beneficial and damaging
changes to human health.
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4.11.1
Discovery
The discovery of UV radiation was intimately associated with the observation that silver
salts darken when exposed to sunlight. In 1801 the German physicist Johann Wilhelm
Ritter made the hallmark observation that invisible rays just beyond the violet end of the
visible spectrum were especially effective at darkening silver chloride-soaked paper. He
called them "de-oxidizing rays" to emphasize their chemical reactivity and to distinguish
them from "heat rays" at the other end of the visible spectrum. The simpler term
"chemical rays" was adopted shortly thereafter, and it remained popular throughout the
19th century. The terms chemical and heat rays were eventually dropped in favor of
ultraviolet and infrared radiation, respectively.
4.11.2
Origin of term
The name means "beyond violet" (from Latin ultra, "beyond"), violet being the colour of
the shortest wavelengths of visible light. UV light has a shorter wavelength than that of
violet light.
4.11.3
Subtypes
The electromagnetic spectrum of ultraviolet light can be subdivided in a number of ways.
The draft ISO standard on determining solar irradiances (ISO-DIS-21348) describes the
following ranges:
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Name
Abbreviation
UVA
Wavelength range
in nanometers
400 nm – 315 nm
Energy per
photon
3.10 – 3.94 eV
Ultraviolet A
Long wave/ Black light
Near
Ultraviolet B or
medium wave
Middle
Ultraviolet C, short
wave, or germicidal
Far
Vacuum
Extreme
NUV
UVB
400 nm – 300 nm
315 nm – 280 nm
3.10 – 4.13 eV
3.94 – 4.43 eV
MUV
UVC
300 nm – 200 nm
280 nm – 100 nm
4.13 – 6.20 eV
4.43 – 12.4 eV
FUV
VUV
EUV
200 nm – 122 nm
200 nm – 10 nm
121 nm – 10 nm
6.20 – 10.2 eV
6.20 – 124 eV
10.2 – 124 eV
In photolithography, in laser technology, etc., the term deep ultraviolet or DUV refers to
wavelengths below 300 nm. "Vacuum UV" is so named because it is absorbed strongly
by air and is therefore used in a vacuum. In the long-wave limit of this region, roughly
150–200 nm, the principal absorber is the oxygen in air. Work in this region can be
performed in an oxygen free atmosphere, pure nitrogen being commonly used, which
avoids the need for a vacuum chamber.
4.11.4
Black light
A black light, or Wood's light, is a lamp that emits long wave UV radiation and very little
visible light. Commonly these are referred to as simply a "UV light". Fluorescent black
lights are typically made in the same fashion as normal fluorescent lights except that only
one phosphor is used and the normally clear glass envelope of the bulb may be replaced
by a deep-bluish-purple glass called Wood's glass, a nickel-oxide–doped glass, which
blocks almost all visible light above 400 nanometers. The color of such lamps is often
referred to in the trade as "blacklight blue" or "BLB." This is to distinguish these lamps
from "bug zapper" blacklight ("BL") lamps that don't have the blue Wood's glass. The
phosphor typically used for a near 368 to 371 nanometer emission peak is either
europium-doped strontium fluoroborate (SrB4O7F:Eu2+) or europium-doped strontium
borate (SrB4O7:Eu2+) while the phosphor used to produce a peak around 350 to 353
nanometers is lead-doped barium silicate (BaSi2O5:Pb+). "Blacklight Blue" lamps peak
at 365 nm.
While "black lights" do produce light in the UV range, their spectrum is confined to the
longwave UVA region. Unlike UVB and UVC, which are responsible for the direct DNA
damage that leads to skin cancer, black light is limited to lower energy, longer waves and
does not cause sunburn. However, UVA is capable of causing damage to collagen fibers
and destroying vitamin A in skin.
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A black light may also be formed by simply using Wood's glass instead of clear glass as
the envelope for a common incandescent bulb. This was the method used to create the
very first black light sources.
Some UV fluorescent bulbs specifically designed to attract insects for use in bug zappers
use the same near-UV emitting phosphor as normal blacklights, but use plain glass
instead of the more expensive Wood's glass. Plain glass blocks less of the visible
mercury emission spectrum, making them appear light blue to the naked eye. These
lamps are referred to as "blacklight" or "BL" in most lighting catalogs.
Ultraviolet light can also be generated by some light-emitting diodes.
4.11.5
Natural sources of UV
The Sun emits ultraviolet radiation in the UVA, UVB, and UVC bands, but because of
absorption in the atmosphere's ozone layer, 98.7% of the ultraviolet radiation that reaches
the Earth's surface is UVA. (Some of the UVB and UVC radiation is responsible for the
generation of the ozone layer.)
Ordinary glass is partially transparent to UVA but is opaque to shorter wavelengths while
Silica or quartz glass, depending on quality, can be transparent even to vacuum UV
wavelengths. Ordinary window glass passes about 90% of the light above 350 nm, but
blocks over 90% of the light below 300 nm.
4.11.6
Human health-related effects of UV radiation
Beneficial effects
The Earth's atmosphere blocks UV radiation from penetrating through the atmosphere by
98.7%. A positive effect of UVB exposure is that it induces the production of vitamin D
in the skin. It has been estimated that tens of thousands of premature deaths occur in the
United States annually from a range of cancers due to vitamin D deficiency. Another
effect of vitamin D deficiency is osteomalacia (the adult equivalent of rickets), which can
result in bone pain, difficulty in weight bearing and sometimes fractures. Other studies
show most people get adequate Vitamin D through food and incidental exposure.
Many countries have fortified certain foods with Vitamin D to prevent deficiency. Eating
fortified foods or taking a dietary supplement pill is usually preferred to UVB exposure,
due to the increased risk of skin cancer from UV radiation.
Too little UVB radiation leads to a lack of Vitamin D. Too much UVB radiation leads to
direct DNA damages and sunburn. An appropriate amount of UVB (What is appropriate
depends on your skin colour) leads to a limited amount of direct DNA damage. This is
recognized and repaired by the body. Then the melanin production is increased which
leads to a long lasting tan. This tan occurs with a 2 day lag phase after irradiation, but it
is much less harmful and long lasting than the one obtained from UVA.
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Harmful effects
An overexposure to UVB radiation can cause sunburn and some forms of skin cancer. In
humans, prolonged exposure to solar UV radiation may result in acute and chronic health
effects on the skin, eye, and immune system. However the most deadly form - malignant
melanoma - is mostly caused by the indirect DNA damage (free radicals and oxidative
stress). This can be seen from the absence of a UV-signature mutation in 92% of all
melanoma.
UVC rays are the highest energy, most dangerous type of ultraviolet light. Little attention
has been given to UVC rays in the past since they are filtered out by the atmosphere.
However, their use in equipment such as pond sterilization units may pose an exposure
risk, if the lamp is switched on outside of its enclosed pond sterilization unit.
Skin : UVA, UVB and UVC can all damage collagen fibers and thereby accelerate aging
of the skin. Both UVA and UVB destroy vitamin A in skin which may cause further
damage. In the past UVA was considered less harmful, but today it is known, that it can
contribute to skin cancer via the indirect DNA damage (free radicals and reactive oxygen
species). It penetrates deeply but it does not cause sunburn. UVA does not damage DNA
directly like UVB and UVC, but it can generate highly reactive chemical intermediates,
such as hydroxyl and oxygen radicals, which in turn can damage DNA. Because it does
not cause reddening of the skin (erythema) it cannot be measured in the SPF testing.
There is no good clinical measurement of the blocking of UVA radiation, but it is
important that sunscreen block both UVA and UVB.
UVB light can cause direct DNA damage. The radiation excites DNA molecules in skin
cells, causing aberrant covalent bonds to form between adjacent cytosine bases,
producing a dimer. When DNA polymerase comes along to replicate this strand of DNA,
it reads the dimer as "AA" and not the original "CC". This causes the DNA replication
mechanism to add a "TT" on the growing strand. This is a mutation, which can result in
cancerous growths and is known as a "classical C-T mutation". The mutations that are
caused by the direct DNA damage carry a UV signature mutation that is commonly seen
in skin cancers. The mutagenicity of UV radiation can be easily observed in bacteria
cultures. This cancer connection is one reason for concern about ozone depletion and the
ozone hole. UVB causes some damage to collagen but at a very much slower rate than
UVA.
Eye :High intensities of UVB light are hazardous to the eyes, and exposure can cause
welder's flash (photokeratitis or arc eye) and may lead to cataracts, pterygium, and
pinguecula formation.
Protective eyewear is beneficial to those who are working with or those who might be
exposed to ultraviolet radiation, particularly short wave UV.
4.11.7
Degradation of polymers, pigments and dyes
Many polymers used in consumer products are degraded by UV light, and need addition
of UV absorbers to inhibit attack, especially if the products are used externally and so
77
exposed to sunlight. The problem appears as discoloration or fading, cracking and
sometimes, total product disintegration if cracking has proceeded far enough. The rate of
attack increases with exposure time and sunlight intensity.
It is known as UV degradation, and is one form of polymer degradation. Sensitive
polymers include thermoplastics, such as polypropylene and polyethylene as well as
speciality fibres like aramids. UV absorption leads to chain degradation and loss of
strength at sensitive points in the chain structure. They include tertiary carbon atoms,
which in polypropylene occur in every repeat unit.
In addition, many pigments and dyes absorb UV and change colour, so paintings and
textiles may need extra protection both from sunlight and fluorescent lamps, two
common sources of UV radiation. Old and antique paintings such as watercolour
paintings for example, usually need to be placed away from direct sunlight. Common
window glass provides some protection by absorbing some of the harmful UV, but
valuable artifacts need shielding.
4.11.8
Blockers and absorbers
Ultraviolet Light Absorbers (UVAs) are molecules used in organic materials (polymers,
paints, etc.) to absorb UV light in order to reduce the UV degradation (photo-oxidation)
of a material. A number of different UVAs exist with different absorption properties.
UVAs can disappear over time, so monitoring of UVA levels in weathered materials is
necessary.
In sunscreen, ingredients which absorb UVA/UVB rays, such as avobenzone and octyl
methoxycinnamate, are known as absorbers. They are contrasted with physical
"blockers" of UV radiation such as titanium dioxide and zinc oxide.
4.11.9
Applications of UV
Security
To help thwart counterfeiters, sensitive documents (e.g. credit cards, driver's licenses,
passports) may also include a UV watermark that can only be seen when viewed under a
UV-emitting light. Passports issued by most countries usually contain UV sensitive inks
and security threads. Visa stamps and stickers on passports of visitors contain large and
detailed seals invisible to the naked eye under normal lights, but strongly visible under
UV illumination. Passports issued by many nations have UV sensitive watermarks on all
pages of the passport. Currencies of various countries' banknotes have an image, as well
as many multicolored fibers, that are visible only under ultraviolet light.
Fluorescent lamps
Fluorescent lamps produce UV radiation by ionising low-pressure mercury vapour. A
phosphorescent coating on the inside of the tubes absorbs the UV and converts it to
visible light.
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The main mercury emission wavelength is in the UVC range. Unshielded exposure of the
skin or eyes to mercury arc lamps that do not have a conversion phosphor is quite
dangerous.
The light from a mercury lamp is predominantly at discrete wavelengths. Other practical
UV sources with more continuous emission spectra include xenon arc lamps (commonly
used as sunlight simulators), deuterium arc lamps, mercury-xenon arc lamps, metalhalide arc lamps, and tungsten-halogen incandescent lamps.
Astronomy
In astronomy, very hot objects preferentially emit UV radiation. Because the ozone layer
blocks many UV frequencies from reaching telescopes on the surface of the Earth, most
UV observations are made from space.
Biological surveys and pest control
Some animals, including birds, reptiles, and insects such as bees, can see into the near
ultraviolet. Many fruits, flowers, and seeds stand out more strongly from the background
in ultraviolet wavelengths as compared to human color vision. Scorpions glow or take on
a yellow to green color under UV illumination. Many birds have patterns in their
plumage that are invisible at usual wavelengths but observable in ultraviolet, and the
urine and other secretions of some animals, including dogs, cats, and human beings, is
much easier to spot with ultraviolet.
Many insects use the ultraviolet wavelength emissions from celestial objects as
references for flight navigation. A local ultraviolet emissor will normally disrupt the
navigation process and would eventually attract to itself the flying insect.
Ultraviolet traps are used to eliminate various small flying insects. They are attracted to
the UV light, and are killed using an electric shock, or trapped once they come into
contact with the device. Different designs of ultraviolet light traps are also used by
entomologists for collecting nocturnal insects during faunistic survey studies.
Spectrophotometry
UV/ VIS spectroscopy is widely used as a technique in chemistry, to analyze chemical
structure, most notably conjugated systems. UV radiation is often used in visible
spectrophotometry to determine the existence of fluorescence in a given sample.
Analyzing minerals
Ultraviolet lamps are also used in analyzing minerals, gems, and in other detective work
including authentication of various collectibles. Materials may look the same under
visible light, but fluoresce to different degrees under ultraviolet light; or may fluoresce
differently under short wave ultraviolet versus long wave ultraviolet.
Chemical markers
79
UV fluorescent dyes are used in many applications (for example, biochemistry and
forensics). The Green Fluorescent Protein (GFP) is often used in genetics as a marker.
Many substances, such as proteins, have significant light absorption bands in the
ultraviolet that are of use and interest in biochemistry and related fields. UV-capable
spectrophotometers are common in such laboratories.
Photochemotherapy
Exposure to UVA light while the skin is hyper-photosensitive by taking psoralens is an
effective treatment for psoriasis called PUVA. Due to psoralens potentially causing
damage to the liver, PUVA may only be used a limited number of times over a patient's
lifetime
Phototherapy
Ultraviolet radiation has other medical applications, in the treatment of skin conditions
such as psoriasis and vitiligo. UVA radiation can be used in conjunction with psoralens
(PUVA treatment). UVB radiation is rarely used in conjunction with psoralens. In cases
of psoriasis and vitiligo, UV light with wavelength of 311 nm is most effective.
Exposure to UVB light, particularly the 310 nm narrowband UVB range, is an effective
long-term treatment for many skin conditions like psoriasis, vitiligo, eczema, and many
others. UVB phototherapy does not require additional medications or topical preparations
for the therapeutic benefit; only the light exposure is needed. However, phototherapy can
be effective when used in conjunction with certain topical treatments such as anthralin,
coal tar, and Vitamin A and D derivatives, or systemic treatments such as methotrexate
and soriatane.
Typical treatment regimes involve short exposure to UVB rays 3 to 5 times a week at a
hospital or clinic, and for the best results, up to 30 or more sessions may be required.
Photolithography
Ultraviolet radiation is used for very fine resolution photolithography, a procedure where
a chemical known as a photoresist is exposed to UV radiation which has passed through a
mask. The light allows chemical reactions to take place in the photoresist, and after
development (a step that either removes the exposed or unexposed photoresist), a
geometric pattern which is determined by the mask remains on the sample. Further steps
may then be taken to "etch" away parts of the sample with no photoresist remaining.
UV radiation is used extensively in the electronics industry because photolithography is
used in the manufacture of semiconductors, integrated circuit components and printed
circuit boards.
Checking electrical insulation
A new application of UV is to detect corona discharge (often simply called "corona") on
electrical apparatus. Degradation of insulation of electrical apparatus or pollution causes
80
corona, wherein a strong electric field ionizes the air and excites nitrogen molecules,
causing the emission of ultraviolet radiation. The corona degrades the insulation level of
the apparatus. Corona produces ozone and to a lesser extent nitrogen oxide which may
subsequently react with water in the air to form nitrous acid and nitric acid vapour in the
surrounding air.
Sterilization
Ultraviolet lamps are used to sterilize workspaces and tools used in biology laboratories
and medical facilities. A low pressure mercury vapor discharge tube floods the inside of a
hood with shortwave UV light when not in use, sterilizing microbiological contaminants
from irradiated surfaces.
Disinfecting drinking water
UV radiation can be an effective viricide and bactericide. Disinfection using UV
radiation is commonly used in wastewater treatment applications and is finding an
increased usage in drinking water treatment. Many bottlers of spring water use UV
disinfection equipment to sterilize their water.
Food processing
As consumer demand for fresh and "fresh-like" food products increases, the demand for
nonthermal methods of food processing is likewise on the rise. In addition, public
awareness regarding the dangers of food poisoning is also raising demand for improved
food processing methods. Ultraviolet radiation is used in several food processes to kill
unwanted microorganisms.
Fire detection
UV detectors are sensitive to most fires, including hydrocarbons, metals, sulfur,
hydrogen, hydrazine, and ammonia. Arc welding, electrical arcs, lightning, X-rays used
in nondestructive metal testing equipment (though this is highly unlikely), and
radioactive materials can produce levels that will activate a UV detection system. The
presence of UV-absorbing gases and vapors will attenuate the UV radiation from a fire,
adversely affecting the ability of the detector to detect flames.
Ultraviolet detectors generally use either a solid-state device, such as one based on
silicon carbide or aluminium nitride, or a gas-filled tube as the sensing element. UV
detectors which are sensitive to UV light in any part of the spectrum respond to
irradiation by sunlight and artificial light. Virtually all fires emit some radiation in the
UVB band, while the Sun's radiation at this band is absorbed by the Earth's atmosphere.
The result is that the UV detector is "solar blind", meaning it will not cause an alarm in
response to radiation from the Sun, so it can easily be used both indoors and outdoors.
Curing of inks, adhesives, varnishes and coatings
81
Certain inks, coatings and adhesives are formulated with photoinitiators and resins. When
exposed to the correct energy and irradiance in the required band of UV light,
polymerization occurs, and so the adhesives harden or cure. Usually, this reaction is very
quick, a matter of a few seconds. Applications include glass and plastic bonding, optical
fiber coatings, the coating of flooring, UV Coating and paper finishes in offset printing,
and dental fillings.
Deterring substance abuse in public places
UV lights have been installed in some parts of the world in public restrooms, and on
public transport, for the purpose of deterring substance abuse. The blue color of these
lights, combined with the fluorescence of the skin, make it harder for intravenous drug
users to find a vein. The efficacy of these lights for that purpose has been questioned,
with some suggesting that drug users simply find a vein outside the public restroom and
mark the spot with a marker for accessibility when inside the restroom. There is currently
no published evidence supporting the idea of a deterrent effect.
Erasing EPROM modules
Some EPROM (electronically programmable read-only memory) modules are erased by
exposure to UV radiation. These modules often have a transparent glass (quartz) window
on the top of the chip that allows the UV radiation in. These have been largely
superseded by EEPROM and flash memory chips in most devices.
Preparing low surface energy polymers
UV radiation is useful in preparing low surface energy polymers for adhesives. Polymers
exposed to UV light will oxidize thus raising the surface energy of the polymer. Once the
surface energy of the polymer has been raised, the bond between the adhesive and the
polymer will not be smaller.
Reading otherwise illegible papyruses
Using multi-spectral imaging it is possible to read illegible papyruses, such as the burned
papyruses of the Villa of the Papyri or of Oxyrhynchus. The technique involves taking
pictures of the illegible papyruses using different filters in the infrared or ultraviolet
range, finely tuned to capture certain wavelengths of light. Thus, the optimum spectral
portion can be found for distinguishing ink from paper on the papyrus surface.
Lasers
Ultraviolet lasers have applications in industry (laser engraving), medicine (dermatology
and keratectomy), free air secure communications and computing (optical storage). They
can be made by applying frequency conversion to lower-frequency lasers.
4.12
SEA LEVEL RISE
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Sea-level rise is an increase in sea level. Multiple complex factors may influence this
change.
Sea-level has risen about 130 meters (400 ft) since the peak of the last ice age about
18,000 years ago. Most of the rise occurred before 6,000 years ago. From 3,000 years
ago to the start of the 19th century sea level was almost constant, rising at 0.1 to 0.2
mm/yr. Since 1900 the level has risen at 1 to 2 mm/yr; since 1993 satellite altimetry from
TOPEX/ Poseidon indicates a rate of rise of 3.1 ± 0.7 mm per yr. Church and White in
2006 found a sea-level rise from January 1870 to December 2004 of 195 mm, a 20th
century rate of sea-level rise of 1.7 ± 0.3 mm per yr and a significant acceleration of sealevel rise of 0.013 ± 0.006 mm per year. If this acceleration remains constant, then the
1990 to 2100 rise would range from 280 to 340 mm.
Sea-level rise can be a product of global warming through two main processes: thermal
expansion of sea water and widespread melting of land ice. Global warming is predicted
to cause significant rises in sea level over the course of the twenty-first century.
4.12.1
Overview of sea-level change
Local and eustatic sea level change
Local mean sea level (LMSL) is defined as the height of the sea with respect to a land
benchmark, averaged over a period of time (such as a month or a year) long enough that
fluctuations caused by waves and tides are smoothed out. One must adjust perceived
changes in LMSL to account for vertical movements of the land, which can be of the
same order (mm/yr) as sea level changes. Some land movements occur because of
isostatic adjustment of the mantle to the melting of ice sheets at the end of the last ice
age. The weight of the ice sheet depresses the underlying land, and when the ice melts
away the land slowly rebounds. Atmospheric pressure, ocean currents and local ocean
temperature changes also can affect LMSL.
“Eustatic” change (as opposed to local change) results in an alteration to the global sea
levels, such as changes in the volume of water in the world oceans or changes in the
volume of an ocean basin.
Short term and periodic changes
There are many following factors which can produce short-term (a few minutes to 14
months) changes in sea level.
I
Short-term (periodic) causes
Periodic sea level changes
Diurnal and semidiurnal astronomical tides
Long-period tides
Rotational variations (Chandler wobble)
Time scale
(P = period)
Vertical effect
12–24 h P
0.2–10+ m
14 month P
83
Meteorological and oceanographic fluctuations
Atmospheric pressure
Hours to months
Winds (storm surges)
1–5 days
Evaporation and precipitation (may also
Days to weeks
follow long-term pattern)
Ocean surface topography (changes in water
Days to weeks
density and currents)
6 mo every 5–10
El Niño/southern oscillation
yr
Seasonal variations
Seasonal water balance among oceans
(Atlantic, Pacific, Indian)
Seasonal variations in slope of water
surface
River runoff/floods
2 months
Seasonal
water
density
changes
6 months
(temperature and salinity)
Seiches
Seiches (standing waves)
Minutes to hours
Earthquakes
Tsunamis (generate catastrophic longHours
period waves)
Abrupt change in land level
Minutes
–0.7 to 1.3 m
Up to 5 m
Up to 1 m
Up to 0.6 m
1m
0.2 m
Up to 2 m
Up to 10 m
Up to 10 m
Longer term changes
Various factors affect the volume or mass of the ocean, leading to long-term changes in
eustatic sea level. The two primary influences are temperature (because the volume of
water depends on temperature), and the mass of water locked up on land and sea as fresh
water in rivers, lakes, glaciers, polar ice caps, and sea ice. Over much longer geological
timescales, changes in the shape of the oceanic basins and in land/sea distribution will
affect sea level.
Observational and modelling studies of mass loss from glaciers and ice caps indicate a
contribution to sea-level rise of 0.2 to 0.4 mm/yr averaged over the 20th century.
Glaciers and ice caps
Each year about 8 mm (0.3 inch) of water from the entire surface of the oceans falls into
the Antarctica and Greenland ice sheets as snowfall. If no ice returned to the oceans, sea
level would drop 8 mm every year. Although approximately the same amount of water
returns to the ocean in icebergs and from ice melting at the edges, scientists do not know
which is greater — the ice going in or the ice coming out. The difference between the ice
input and output is called the mass balance and is important because it causes changes in
global sea level.
84
Geological influences
At times during Earth's long history, continental drift has arranged the land masses into
very different configurations from those of today. When there were large amounts of
continental crust near the poles, the rock record shows unusually low sea levels during
ice ages, because there was lots of polar land mass upon which snow and ice could
accumulate. During times when the land masses clustered around the equator, ice ages
had much less effect on sea level. However, over most of geologic time, long-term sea
level has been higher than today. Only at the Permian-Triassic boundary ~250 million
years ago was long-term sea level lower than today. Long term changes in sea level are
the result of changes in the oceanic crust, with a downward trend expected to continue in
the very long term.
During the glacial/interglacial cycles over the past few million years, sea level has varied
by somewhat more than a hundred metres. This is primarily due to the growth and decay
of ice sheets (mostly in the northern hemisphere) with water evaporated from the sea.
85
Long-term causes
Range
effect
of Vertical
effect
Change in volume of ocean basins
Plate tectonics and seafloor spreading (plate
divergence/convergence) and change in seafloor Eustatic
elevation (mid-ocean volcanism)
0.01
mm/yr
Marine sedimentation
Eustatic
<
0.01
mm/yr
Change in mass of ocean water
Melting or accumulation of continental ice
• Climate changes during the 20th century
Eustatic
10 mm/yr
•• Antarctica (the results of increasing precipitation)
Eustatic
•• Greenland (from changes in both precipitation and
runoff)
• Long-term adjustment to the end of the last ice age
•• Greenland and Antarctica contribution over 20th
century
Release of water from earth's interior
Release or accumulation of continental hydrologic
reservoirs
Uplift or subsidence of Earth's surface (Isostasy)
Thermal-isostasy (temperature/density changes in
earth's interior)
Glacio-isostasy (loading or unloading of ice)
Hydro-isostasy (loading or unloading of water)
Volcano-isostasy (magmatic extrusions)
Sediment-isostasy (deposition and erosion of
sediments)
Tectonic uplift/subsidence
Vertical and horizontal motions of crust (in response to
fault motions)
Sediment compaction
Sediment compression into denser matrix (particularly
significant in and near river deltas)
Loss of interstitial fluids (withdrawal of groundwater or
oil)
Earthquake-induced vibration
Departure from geoid
Shifts in hydrosphere, aesthenosphere, core-mantle
interface
Shifts in earth's rotation, axis of spin, and precession of
Eustatic
Eustatic
-0.2 to 0.0
mm/yr
0.0 to 0.1
mm/yr
0.0 to 0.5
mm/yr
Eustatic
Eustatic
Local effect
Local effect
Local effect
Local effect
10 mm/yr
Local effect
<
mm/yr
Local effect
1-3
mm/yr
4
Local effect
Local effect
≤
55
mm/yr
Local effect
Local effect
Eustatic
86
equinox
External gravitational changes
Eustatic
Evaporation and precipitation (if due to a long-term
Local effect
pattern)
4.12.2
Effects of sea level rise
Based on the projected increases stated above, the The Intergovernmental Panel on
Climate Change (IPCC) report notes that current and future climate change would be
expected to have a number of impacts, particularly on coastal systems. Such impacts may
include increased coastal erosion, higher storm-surge flooding, inhibition of primary
production processes, more extensive coastal inundation, changes in surface water
quality and groundwater characteristics, increased loss of property and coastal habitats,
increased flood risk and potential loss of life, loss of nonmonetary cultural resources and
values, impacts on agriculture and aquaculture through decline in soil and water quality,
and loss of tourism, recreation, and transportation functions.
There is an implication that many of these impacts will be detrimental. The report does,
however, note that owing to the great diversity of coastal environments; regional and
local differences in projected relative sea level and climate changes; and differences in
the resilience and adaptive capacity of ecosystems, sectors, and countries, the impacts
will be highly variable in time and space and will not necessarily be negative in all
situations.
Statistical data on the human impact of sea level rise is scarce. A study in the April, 2007
issue of Environment and Urbanization reports that 634 million people live in coastal
areas within 30 feet (9.1 m) of sea level. The study also reported that about two thirds of
the world's cities with over five million people are located in these low-lying coastal
areas.
Drowning of Islands
IPCC assessments suggest that deltas and small island states are particularly vulnerable
to sea level rise caused by both thermal expansion and ocean volume. Relative sea level
rise (mostly caused by subsidence) is currently causing substantial loss of lands in some
deltas. Sea level changes have not yet been conclusively proven to have directly resulted
in environmental, humanitarian, or economic losses to small island states, but the IPCC
and other bodies have found this a serious risk scenario in coming decades.
Many reports have focused the island nations of the Pacific, notably the Polynesian
island of Tuvalu, which based on more severe flooding events in recent years, was
thought to be "sinking" due to sea level rise. A scientific review in 2000 reported that
based on University of Hawaii gauge data, Tuvalu had experienced a negligible increase
in sea-level of 0.07 mm a year over the past two decades, and that ENSO had been a
larger factor in Tuvalu's higher tides in recent years. A subsequent study by John Hunter
from the University of Tasmania, however, adjusted for ENSO effects and the movement
of the gauge (which was thought to be sinking). Hunter concluded that Tuvalu had been
87
experiencing sea-level rise of about 1.2 mm per year. The recent more frequent flooding
in Tuvalu may also be due to an erosional loss of land during and following the actions of
1997 cyclones Gavin, Hina, and Keli.
4.12.3
Sea Level Measurement through Satellite
Sea level rise estimates from satellite altimetry are 3.1 +/- 0.4 mm/ yr for 1993-2003
(Leuliette et al. (2004)). This exceeds those from tide gauges. It is unclear whether this
represents an increase over the last decades; variability; true differences between
satellites and tide gauges; or problems with satellite calibration.
Since 1992 the NASA/ CNES TOPEX/ Poseidon (T/P) and Jason-1 satellite programs
have provided measurements of sea level change. The data show a mean sea level
increase of 2.8 ± 0.4 mm/ yr. This includes an apparent increase to 3.7 ± 0.2 mm/ yr
during the period 1999 through 2004. Satellites ERS-1 (July 17, 1991-March 10, 2000),
ERS-2 (April 21, 1995-), and Envisat (March 1, 2002-) also have sea surface altimeter
components but are of limited use for measuring global mean sea level due to less
detailed coverage. TOPEX/ Poseidon began their series of measurements in 1992, and
the scientific mission was ended in October 2005. Jason-1, launched December 7, 2001,
has now taken over the mission, and is flying the same ground track.
4.13
LET US SUM UP
1.
2.
3.
4.
5.
Living organisms and physical surroundings, with which one interacts, form the
environment,
Pollutants are substances that adversely change the environment. They are are
biodegradable and non-biodegradable,
Pollution is an undesirable change in physical, chemical and biological
characteristics of air, water, and land,
Air pollution results from a variety of causes, not all of which are within human
control. Dust storms in desert areas and smoke from forest fires and grass fires
contribute to chemical and particulate pollution of the air. The source of pollution
may be in one country but the impact of pollution may be felt elsewhere,
Air pollution is aggravated because of four developments: increasing traffic,
growing cities, rapid economic development, and industrialization. Modernisation
and progress have led to air getting more and more polluted over the years. Industries,
vehicles, increase in the population, and urbanization are some of the major factors
responsible for air pollution,
6.
The problem of contamination of drinking water with heavy metals
particularly arsenic is increasing day by day and has now taken the form of
National calamity,
7.
Sunderban Biosphere Reserve is badly affected by arsenic contamination
and concrete efforts and effective measures must be taken to protect this
calamity,
8.
Stratospheric ozone depletion due to air pollution has long been recognized as a
threat to human health as well as to the Earth's ecosystems,
88
9.
Different techniques and practices are adopted to control pollution,
10.
Population and development affect the environment. There is a need for
proper planning to maintain balance between population, development and
environment,
11.
Conservation relates to activities of human beings and judicious use of
national resources,
12.
Government has enacted various efforts, laws and acts to conserve and
protect the environment.
89
4.14
CHECK YOUR PROGRESS AND THE KEY
Tick the correct answer :
1. The concentration of CO2 in atmosphere is :?
(a) 30 ppm
(b) 300 ppm
(c) 3000 ppm
(d)
3
ppm
2. Green house effect is leading to :
(a) Increase in temp.
(b) Decrease in temp.
(c) Maintaining the temp.
(d) None of above
3. Ozone (O3) is formed in which zone of atmosphere :
(a) Mesosphere
(b) Stratosphere
(c) Troposphere
(d) Ionosphere
4. What is correct sequence of different zones of atmosphere from below ?
(a) Troposphere, Stratosphere, Mesosphere, Ionosphere
(b) Stratosphere, Troposphere, Ionosphere, Mesosphere,
(c) Mesosphere, Stratosphere, Troposphere, Ionosphere
(d) Ionosphere, Mesosphere, Stratosphere, Troposphere
5. Out of several gases present in the atmosphere, plants mostly depend :
(a) On concentration of O2 for respiration
(b) On amount of N2
(c) On CO2 concentration
(d) On availability of CO2
Key :
4.15
1.
(b) 300 ppm
2.
(a) Increase in temp.
3.
(b) Stratosphere
4.
(a) Troposphere, Stratosphere, Mesosphere, Ionosphere
5.
(c) On CO2 concentration
ASSIGNMENTS / ACTIVITIES
90
It is compulsory for every student to complete an assignment/ activity/ project work from
any known prospects of environmental pollution or climate change. Write details in
following (any one):
1.
1.
Gaseous composition of atmosphere and composition of polluted air
Environmental pollutant and types of pollution are on the
priority areas of India
2.
Sources, trends and control method of water and soil
pollution
3.
Ozone: useful or harmful to us? Discuss the threats to its
depletion in atmosphere
4.
Photochemical smog and Acid rains
5.
Ultraviolet and its application
6.
Pollution control laws
7.
Sea level rise and its measurements through satellite.
4.16
REFERENCES / FURTHER READINS
1.
Adriano D C, Bollag J M, Frankenberger W T and Sims R C. (1999).
Bioremediation of Contaminated Soils, Agronomy monographs 37 (eds). American
Society of Agronomy.
2.
Arendt (July 2002). Rapid Wastage of Alaska Glaciers and Their
Contribution to Rising Sea Level. Science 297: 382-386.
3.
Beychok M R (2005). Fundamentals of Stack Gas Dispersion 4th Edition.
Author-published. Available from http://www.air-dispersion.com
4.
Bindoff N L (2007). Oceanic climate change and sea level climate change
2007 : the physical science basis. Contribution of Working Group I to the Fourth
Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge
University Press.
5.
Emanuel K A (2005). Increasing destructiveness of tropical cyclones over
the past 30 years Nature 436 (7051): 686–688.
6.
Emery K O and Aubrey D G (1991). Sea levels, land levels, and tide
gauges. New York : Springer-Verlag.
7.
Environmental Quality Standards for Soil Pollution, Ministry of
Environment & Forests available from http://www.envfor.nic.in
Frank K, Brass M, Hamilton J, Röckmann T (2006). Global Warming The Blame Is not with the Plants, Max Planck Society.
8.
9.
Intergovernmental Panel on Climate Change (2001). Climate change 2001:
the scientific basis.
91
10.
Karnaukhov A V (2001). Role of the Biosphere in the Formation of the
Earth’s Climate: The Greenhouse Catastrophe. Biophysics 46 (6).
11.
Laury M and Bruce C D (2004). Mass and volume contributions to
twentieth-century global sea level rise. Nature 428: 406-409.
12.
Lerner B W (2006). Environmental issues: essential primary sources.
Thomson Gale.
13.
Miller R W and Gardiner D T (1998). Soils in Our Environment 8th
edition. Upper Saddle River, NJ: Prentice Hall.
14.
Müller R D (2008). Long-Term Sea-Level Fluctuations Driven by Ocean
Basin Dynamics. Science 319: 1357–1362.
15.
Oreskes N (2004). Beyond the Ivory Tower: The Scientific Consensus on
Climate Change. Science 306 (5702): 1686.
Pierzynski G M, Sims J T and Vance G F (2000). Soils and Environmental
Quality 2nd edition. Boca Raton FL: CRC Press.
Raimund M, Joos F, Simon A, Müller I S (2005). Climate: How unusual is
today's solar activity? Nature 436 (7012): 1084–1087.
Ruddiman W F (2005). Earth's Climate Past and Future. New York:
Princeton University Press.
Solanki S K, Usoskin I G, Kromer B, Schussler M and Beer J (2004).
Unusual activity of the Sun during recent decades compared to the previous 11,000
years. Nature 431: 1084–1087.
Solanki S K, Usoskin I G, Kromer B, Schussler M and Beer J (2005).
Climate: How unusual is today's solar activity? (Reply). Nature 436: E4–E5.
16.
17.
18.
19.
20.
21.
Turner D B (1994). Workbook of atmospheric dispersion estimates: an
introduction to dispersion modeling 2nd Edition, CRC Press.
22.
U S Environmental Protection Agency (USEPA) web site: Soil and
Groundwater
Pollution
Remediation
Act
available
from
http://www.epa.gov.tw/english/laws/soil.htm.
23.
Vleeschouwer O (2001). Greenhouses and conservatories Flammarion,
Paris.
24.
Woods M (1988). Glass houses: history of greenhouses, orangeries and
conservatories Aurum Press, London.
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