5.2 THE GREENHOUSE EFFECT
Assessment Statements
Draw and label a diagram of the carbon cycle to show the processes
involved.
Analyze the changes in concentration of atmospheric carbon dioxide
using historical records.
Explain the relationship between rises in concentrations of
atmospheric carbon dioxide, methane and oxides of nitrogen and
the enhanced greenhouse effect.
Outline the precautionary principle.
Evaluate the precautionary principle as a justification for strong
action in response to the threats posed by the enhanced greenhouse
effect.
Outline the consequences of a global temperature rise on arctic
ecosystems.
The Carbon Cycle
Carbon is one of the most important elements that are recycled in
an ecosystem.
Inorganic carbon dioxide in the atmosphere is trapped or “fixed”
as organic carbon compounds during photosynthesis.
Some of the carbon is returned to the atmosphere as the plants
respire.
The other steps in the cycle follow the same path as food chains.
As herbivores eat plants, and carnivores eat herbivores, the
carbon compounds move from plants to animals.
Respiration by any organism in this sequence returns carbon
to the atmosphere as carbon dioxide and when a plant or
animal dies, carbon compounds move to detritivores and
saprotrophs which may also respire.
http://www.youtube.com/watch?v=U3SZKJVKRxQ
http://www.youtube.com/watch?v=Xz0fn81BlIQ
In some conditions, plants and animals do not decay when they die.
They become compressed and fossilized in a process that takes millions of
years and forms fossil fuels.
Vast coal, oil and natural gas deposits have been formed and the carbon
trapped in these fuels cannot return to the atmosphere unless the fuels are
burned.
Over a very long period of time, fossil fuel formation has gradually lowered
the carbon dioxide level of Earth’s atmosphere, but recently this balance has
been upset.
Draw a labeled diagram showing stages of the
carbon cycle. [5]
How the Greenhouse Effect Works
Certain gases, including CO2 enable the atmosphere to retain
heat.
Without these gases in the atmosphere, the Earth’s temperature
would be too low to support life.
The warming effect of these gases is known as the greenhouse
effect because it is works in a similar way a greenhouse works.
A greenhouse is made of glass, which allows shorter-wave radiation from the sun to
pass through it.
As the sunlight passes through the glass, the radiation is changed into heat, which
has a longer wavelength. Glass is less transparent to theses long wavelengths and
heat is trapped in the greenhouse, making it warmer.
The greenhouse gases such as carbon dioxide, methane, and water vapor act the
same way. They trap the heat and keep the temperature comfortable for life to exist.
Greenhouse gases, Human Activity and Global Warming
Carbon dioxide forms only 0.04% of the atmospheric gases but it plays a significant
part in the greenhouse effect.
Other greenhouse gases include water vapor, methane, oxides and fluorocarbons
(FCs).
Chlorofluorocarbons (CFCs) were used in aerosols and as refrigerants but were
found to damage the ozone. They were replaced with hydrofluorcarbons (HFCs), but
HFCs are causing problems because they are a greenhouse gasses.
Human population has increased dramatically in the last hundred
years.
Increased population calls for an increased demand for energy in
industry, transport and homes.
Most of this energy demand has been met by burning fossil fuels,
mainly coal, oil and gas.
Burning fossil fuels releases both carbon dioxide and oxides of nitrogen.
Burning these fuels has raised the concentration of carbon dioxide in
the Earth’s atmosphere by more than 20% since 1959
In the tropical regions of the world vast rainforests trap carbon dioxide
through photosynthesis and have been important in maintaining the low level
of carbon dioxide.
We upset this balance by deforesting vast areas of forests for agriculture and
timber production.
78,000 square miles are lost every year. Forest destruction has multiple
effects, but most important for the atmosphere are the loss of carbon dioxide
uptake and the increase of carbon dioxide released from the rotting or burnt
vegetation.
Another important result of rising carbon dioxide levels is lowering
of the pH of the oceans as carbon dioxide dissolves in them.
Acidic oceans may inhibit the growth of the producers, weakens
shells and coral, which affects the food chains.
Atmospheric Carbon Dioxide levels
Year
CO2 ppm
% increase from
previous year
% increase
from 1959
1959
316
1.3
1.3
1965
320
1.9
3.2
1970
331
1.5
4.7
1980
339
2.4
7.3
1985
346
2.1
9.5
1990
354
2.3
12.0
1995
361
2.0
14.2
2000
369
2.2
16.8
2002
373
1.1
18.0
2004
378
1.3
19.6
2006
382
1.1
20.9
2008
386
1.0
22.2
2012
395
Safe level of atmospheric CO2 is 350ppm.
25
Methane is another important greenhouse gas.
It’s produced by human activity when organic waste decomposes, it also
comes from rice paddies and from cattle farming.
As the human population increases the need for food increases,
resulting in more rice paddies and cattle farming.
Cattle release methane from their digestive systems as they process
their food.
Climatologists are concerned that, as a result of all this activity,
humans are adversely affecting our atmosphere.
Rising levels of greenhouse gases are believed to be causing an
enhancement of the natural greenhouse effect.
Earth is experiencing a rise in average global temperature,
known as global warming, which is thought to be happening
because of this enhanced greenhouse effect.
Global warming is a too simplistic of a term. Some areas of the
world will become colder, a better term is climate change.
Some Results of Climate Change
Melting of ice caps and glaciers
Rising sea levels, causing flooding
Change in the pattern of climate, leading to changes in ecosystems
and the distribution of plants and animals
One liter of gasoline comes from 23.5 tons of ancient organic material.
The total amount of fossil fuels used in 1997 was estimated to have been
produced from all plant matter that grew on the surface and all the oceans of the
ancient Earth from a period of more than 400 years.
Earth’s coal supply will last for 1500, however, with a 5% growth rate will only
last 86. As supplies of other fossil fuels diminish, coal will be used more.
The Precautionary Principle
The precautionary principle suggests that if the effect of a change
caused by humans is likely to be very harmful to the environment,
actions should be taken to prevent it, even if there may not be
sufficient data to prove that the activity will cause harm.
This principle is often applied to the impact of human actions on
the environment and human health, as both are complex and the
consequences may be unpredictable.
The precautionary principle challenges governments, industries
and consumers to take action without waiting for definitive
scientific proof to be forthcoming.
Evaluating the Precautionary Principle
Should the precautionary principle be used to justify action to reduce the
impact of the release of greenhouse gases into the atmosphere before
irreparable harm is done? Here are some arguments to discuss:
1. Climate change has consequences for the entire human race and an
international solution is needed to tackle the problems. It is not always the
case that those who produce the most greenhouse gases suffer the greatest
harm so it is essential that measures to reduce emissions are taken with
full international cooperation.
2. If industries and farmers in one area invest money to reduce their
greenhouse gases while those in other areas don’t, an economic imbalance
may be created in favor of the more polluting enterprises, who can offer
services more cheaply.
3. Consumers can be encouraged to use more environmentally friendly goods
and services.
4. It is unethical for one generation to cause harm to future generations by
not taking actions to address the problem of greenhouse gases.
5. Scientists can argue that it is better to invest in a sustainable future and
prevent further harm.
Global Temperature rise and Arctic Ecosystems
The ecosystems of the Arctic include the tundra, permafrost and the sea ice
in the north Pole.
Records have shown considerable changes in recent years. Average annual
temperatures in the Arctic have increased by double the increase in global
temperatures, which results in the melting of sea ice and glaciers.
Melting sea ice affects many species. Algae, which hare important
producers in Arctic food chains, are found just beneath the sea ice.
As ice disappears, so do the algae and this affects numerous other
organisms that use them as food.
Populations of marine mammals, caribou and polar bears are also
affected.
Caribou are falling through once-solid sea ice and polar bears which live
on sea ice while hunting for prey, now have shorter feeling periods and
decreased access to seals that they hunt.
Polar bears numbers are decreasing at an alarming rate.
Forest and tundra ecosystems are important features of the Arctic environment.
In Alaska, substantial changes in forest life, including increases in insect pests.
Rising temperatures have allowed spruce bark beetles to reproduce rapidly, one
outbreak caused the loss of over 2.3 million acres of trees.
Detritus, which is dead organic matter is trapped in the frozen tundra is
released as the ground thaws. The detritus decomposers and the carbon dioxide
and methane producers are released into the atmosphere, adding to the rising
greenhouse gas levels.
Explain the relationship between rises in
concentration of atmospheric gases and the
enhanced greenhouse effect. [8]
Award [2 max] from the following list of greenhouse gases:
water vapour;
carbon dioxide;
methane;
oxides of nitrogen;
all (of these gases) occur naturally;
and human activity has increased the normal level of these gases
in recent years;
incoming shorter wave radiation from the Sun;
is re-radiated as longer wave radiation/infrared;
(mainly) in the form of heat;
captured by greenhouse gases;
which increases the atmospheric/ocean temperature;
at a higher rate than normal / creating a positive imbalance;
which threatens ecosystems/climatic patterns/ocean patterns;
Earth’s history had many fluctuations in gas levels/global
temperature / some
scientists are skeptical about enhanced greenhouse effect;
Outline the precautionary principle. [2]
some human-induced change can be very large/perhaps
catastrophic;
those responsible for the change must prove it will cause no
harm before proceeding;
appropriate (environmental/medical etc.) example e.g. companies
must immediately reduce emission of greenhouse gases even
though proof of human impact on global warming is still debated;
is reverse of historical practice / previously those concerned
about change had to prove it will do harm to prevent such
changes from going ahead / paradigm shift; [2 max]
Outline how global warming may affect arctic
ecosystems. [5]
global warming is an increase in temperature of the
atmosphere/oceans/Earth;
may result in climate change / changes in amount of
precipitation / greater ranges in
temperature;
melting ice leads to rising of sea level;
leading to loss of habitat / example of organism that would lose
habitat;
changes in salinity / changes in ocean currents change
distribution of nutrients;
changes in predator-prey relationships (due to ecosystem
disruption);
increased success of pest species;
temperate species with bigger range of habitats as ice melts;
increased rate of decomposition of detritus;
Below is a graph of atmospheric CO2 levels measured at Mauna Loa
Observatory, Hawai’i.
Explain the observed changes in atmospheric CO2 concentration from
1960 to 2005.
[3]
from 1960–2005) atmospheric concentration increases/strong positive trend /
increase between 1960–2005 of 65 ppm/figures to that effect; CO2
released by human activities contributes to the increase; CO2
examples of human activities e.g. combustion of fossil fuels / deforestation;
seasonal/annual fluctuations (do not prevent long-term increase); [3 max]
List 3 groups of organisms in the carbon cycle that transfer
carbon dioxide to the atmosphere.
State the process in the carbon cycle by which carbon dioxide is
fixed as organic carbon-containing compounds.
List 3 greenhouse gases.
List 5 human activities that are causing an increase in the
levels of greenhouse gases in the atmosphere.
List 3 ways in which a rise in average global temperature is
having an effect on Arctic ecosystems.