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Chapter 12 Global climate change
This chapter examines Earth's climate, emphasizing the topic of global warming and how it can change the entire
Earth's climate. Although the global climate has changed in the past, human actions may be playing an increasing
role in Earth's temperature. In fact, human activities have significantly increased the amount of carbon dioxide, a
major greenhouse gas, in the atmosphere. Other greenhouse gases such as ozone, nitrous oxides, and CFCs are
also increasing. Other factors such as Milankovitch cycles and the North Atlantic Deep Water circulation patterns
could also impact Earth's climate, especially if these phenomena are affected by global warming. Scientists use a
wide array of methods, ranging from drilling ice cores to computer simulations, to detail past, present, and future
climatic conditions. Many atmospheric scientists have concluded that Earth has gotten warmer, snow cover has
decreased, and sea levels have risen as a result of warmer temperatures. Predictions of future impacts include
further temperature increases, changed or destroyed ecosystems, water and food shortages, and increased human
health problems and mortality. There is considerable debate, however, on the appropriate responses to climate
change, centered on the economic and political costs of reducing greenhouse gas emissions. Humans can
implement many solutions to reduce greenhouse gas emissions, especially in the electricity production and
transportation sectors. These solutions range from making personal lifestyle decisions to designing more efficient
motors and products. Treaties to reduce carbon dioxide emissions have not been welcomed by all nations, and
carbon dioxide emissions will continue to increase.
Rising Temperatures and Seas May Take the Maldives Under
The Maldives is a series of islands in the Indian Ocean.
These islands have spectacular scenery and an economy that depends mainly on tourism and fishing.
Eighty percent of the islands are less than 1 meter above sea level..
If global warming does cause the sea level to rise, the Maldives could be destroyed-physically, culturally, and
economically.
Coastal areas, including Florida, will also face problems with rising sea levels.
Some people, for example, those in the oil industry, maintain that global warming would help people enjoy a
better life.
Earth's Hospitable Climate
Weather describes an area's short-term conditions (e.g., temperature, wind speed), whereas climate describes an
area's long-term pattern of atmospheric conditions.
Global climate change describes changes in Earth's climate, such as temperature, precipitation, and storm
intensity.
Most scientists agree that human activities, such as fossil-fuel combustion and deforestation, are altering Earth's
atmosphere and climate.
The sun and the atmosphere keep Earth warm
Earth's climate is affected by the sun, atmosphere, and oceans.
About 30% of the sun's radiation is reflected back into space by Earth's atmosphere.
The remaining 70% is absorbed by molecules in the atmosphere or reaches Earth's surface, where it is either
reflected back into space or absorbed.
"Greenhouse gases" warm the lower atmosphere
Some molecules in the atmosphere can absorb solar radiation; for example, ozone {O3) can absorb ultraviolet
radiation.
Carbon dioxide, water vapor, ozone, nitrous oxides, and methane are called greenhouse gases, because they can
absorb infrared radiation released from Earth’s surface and warm it later on.
The greenhouse effect describes the warming of the troposphere and Earth's surface when the atmosphere warms
and then radiates heat back to Earth.
The term "greenhouse effect" is not technically correct, because a greenhouse heats by preventing warm air from
escaping, whereas greenhouse gases absorb and then re-emit infrared radiation, so that heat is absorbed,
transformed, and then radiated.
Global warming describes an increase in Earth's average surface temperature, no matter what causes the increase.
The greenhouse effect is a natural phenomenon, but humans can influence it by increasing the concentration of
infrared-absorbing gases.
Global warming potential describes the relative global warming potential of greenhouse gases; carbon dioxide has
a global warming potential of 1, while methane's global warming potential of 23 means it is 23 times more potent
than carbon dioxide.
Carbon dioxide is the primary greenhouse gas
Human activities have increased the amount of carbon dioxide in the atmosphere by 33%, its highest level in at
least 400,000 years, and the concentration is increasing faster today than in the past 20,000 years.
The two major human activities that have increased atmospheric carbon dioxide are burning fossil fuels and
clearing and burning forests.
When fossil fuel is burned, large amounts of carbon are transferred from underground deposits to the atmosphere
in the form of carbon dioxide. Removing forests reduces the ability of the biosphere to absorb carbon dioxide
from the atmosphere, which increases concentrations in the atmosphere.
Other greenhouse gases add to warming
Methane, another greenhouse gas, is released into the atmosphere by
burning fossil fuels, raising livestock, disposing of organic matter in land- fills, and planting rice crops.
Methane concentrations have increased 151% since 1750, and are at the highest levels in 400,000 years.
Nitrous oxide, from feedlots, industry, automobile emissions, and agriculture, has increased 17%.
Ozone concentrations have increased 36% since 1750.
Chlorofluorocarbons (CFCs) are another group of greenhouse gases, but these are declining because of the
Montreal Protocol.
The most abundant greenhouse gas is water vapor
If temperatures increase, more water vapor will be added to the atmosphere through evaporation, which could
further increase the greenhouse effect.
Aerosols and other elements may exert a cooling effect on the lower atmosphere
Microscopic droplets and particles, called aerosols, can have both a warming and a cooling effect.
Soot aerosols can warm, while aerosols high in the clouds may cool the atmosphere.
Sulfur-rich atmosphere, as well as volcanic aerosols, may reduce the amount of heat reaching the surface of Earth
and may cool the atmosphere.
Feedback loops complicate climate systems
Feedback loops can make global warming more severe, or can actually help cool Earth, depending on the
interactions that occur.
Because of feedback loops, a minor change can lead to major changes in global climate.
The atmosphere is not the only factor that influences global climate
The atmosphere is not the only factor that influences climate; the amount of energy released by the sun and
changes in Earth's rotation can also affect climate.
Milankovitch cycles: Slight variations in Earth's rotation and orbit around the sun are known as Milankovitch
cycles, which cause different amounts of solar energy to reach Earth.
These varying amounts of solar energy affect atmospheric heating and circulation, which ,can trigger everything
from an ice age to much subtler changes.
Oceanic circulation: Oceans can affect Earth's temperature by absorbing enormous amounts of heat from the
atmosphere, and by moving water and heat from one place to another.
At the poles, the oceans emit more heat than they receive, which causes the cooling water to sink, so that the
warmer water from the equator moves toward the poles.
The best-known interactions between the ocean and the atmosphere are phenomena called EI Nino and La Nina.
El Nino occurs when prevailing equatorial winds weaken and allow warm, western Pacific water to move
eastward, which prevents cold water from welling up in the eastern Pacific.
In La Nina, however, cold surface waters extend westward in the equatorial Pacific.
Ocean currents in the northern Atlantic Ocean move warm surface waters from the equator northward, warming
Europe.
As the water releases its heat, it cools and sinks, moving westward in a conveyor-belt-like action.
The North Atlantic Deep Water (NADW) is the deep part of the circulation pattern that moves water and heat
from one place to another.
Interrupting the NADW's formation could trigger rapid climate change, resulting in a rapid cooling of Europe.
Methods of Studying Climate Change
To understand how climate is changing, scientists must understand climate conditions of the past.
Geologic records tell us about the past
Ice cores containing tiny bubbles of ancient atmosphere can provide information about temperature,
greenhouse gas concentrations, and snowfall.
Pollen grains preserved in sediment can reveal the history of past vegetation. Direct atmospheric sampling
analyzes air samples taken at various places throughout Earth to determine atmospheric carbon dioxide
concentrations.
Direct atmospheric sampling tells us about the present
Data shows that atmospheric carbon dioxide concentrations have increased from around 315 ppm to 373 ppm
since 1958.
Coupled general circulation models help us understand climate change Computer programs such as the Coupled General
Circulation Model
(CGCM) can simulate climate change by combining knowledge about the influence of weather patterns,
atmospheric circulation, atmosphere-ocean interactions, and feedback mechanisms.
This type of computer modeling is extremely complex, and only became available with the invention of
supercomputers.
With increased computer power, and by using proxy indicators (indirect evidence such as pollen and air bubbles),
CGCMs are becoming more reliable.
Climate Changes Estimates and Predictions
In 2001, an international panel of atmospheric scientists and other experts called the Intergovernmental Panel on
Climate Change (IPCC) issued a summary of global climate trends.
The IPCC report summarizes evidence of recent changes in global climate The IPCC presented how climate change has
already influenced the weather, the physical Earth and its organisms, and our economies.
The report concluded that (1) Earth's average surface temperature has in- creased; (2) glaciers and snow cover
were melting around the world; and (3) hundreds of species were shifting their geographic ranges and the timing
of their life cycles.
Storm surges, temporary rises in sea level caused by violent weather, will probably increase, which could
endanger millions of humans living along coasts.
If sea levels rise, parts of major U.S. cities such as Houston, Texas, and New Orleans, Louisiana, will be under
water, wetlands will be lost, and forests will be flooded.
Sea-level rise is one of the many impacts that climate change will likely bring about
As glaciers shrink, the water that they held in solid form becomes available in liquid form. A significant increase
in water in the oceans means a significant rise in sea level.
However, rather than glacial melt most of sea-level rise is predicted to be from thermal expansion of water
because water expands as it warms.
The Maldives is not the only nation that will suffer from rising sea levels. Toga, Fiji, the United States, Japan, and
many other nations all predict to lose land.
The IPCC and other groups project future impacts of climate change
In 2000, the U.S. Global Change Research Program (USGCRP) issued a
report predicting future climate changes and their impacts on the United States.
This report predicts increased temperature and precipitation, lost or dramatically changed ecosystems (e.g.,
mountaintop ecosystems and northeastern maple tree forests), decreased water supplies, decreased crop productivity, and increased human mortality
and health problems.
Climate change will affect agriculture and forestry
If average temperatures increase only slightly, tropical and mid-latitude
farms may have decreased agricultural productivity, while higher latitudes may have increased productivity.
With warmer temperatures, forests will become more productive, but forest fires will become more frequent and
intense.
Mountain forests will become less common, while oak-pine forests may expand.
Freshwater ecosystems would also face challenges
Some freshwater ecosystems would show increased erosion, flooding, and saltwater intrusion (the contamination
of groundwater and soils by saltwater).
Marine ecosystems would also be affected
Marine ecosystems, including coral reefs, which provide vital wildlife habitat and protect shorelines from erosion,
would be affected.
The tourism industry, which is built around experiencing coastal environments, would be devastated.
Human health could suffer, or perhaps benefit
Human health could be affected by increased heat stress, tropical diseases
(e.g., malaria), and hunger-related problems as agriculture becomes increasingly stressed.
The heat index, a product of temperature and humidity, will increase, causing more heat strokes, disease
outbreaks, and irritation of the respiratory system from pollutants.
However, fewer cold-related diseases and injuries would occur if the climate warms.
The Debate Concerning Global Climate Change
Despite the agreement among many scientists that Earth's atmosphere and climate are changing, they disagree on
the causes, extent, and impacts of these changes.
More importantly, scientists, politicians, and economists disagree on the appropriate response to these changes.
Scientists agree that climate change is occurring but disagree on some of the details
Although almost all scientists have concluded that humans are altering the atmosphere, and that greenhouse gas
emissions are changing the climate, they disagree on the role that clouds, water vapor, particles, the oceans, and
NADW affect climate.
These uncertainties make it difficult to predict the future climate of Earth.
Global climate change debates occur in the economic and political arenas as well
Policymakers and economists disagree over appropriate responses to climate change.
Some concerns regarding appropriate responses include: What are the costs to the economy of reducing emissions
versus the costs to Earth due to increasing temperatures? Who should shoulder the economic burden of reducing
greenhouse gas emissions? How much will it cost to decrease emissions or cope with climate change?
Some people argue that we need to be much more certain that global warming is occurring and others argue that
reducing greenhouse gas emissions would be too expensive or require too many regulations.
Technological and political Methods of Emissions Reduction
The generation of electricity, mostly through burning coal, has produced the largest source of greenhouse gases,
followed by transportation, industry, and then agriculture.
Electricity generation is the largest source of anthropogenic greenhouse gases in the United States
In the United States, fossil fuels, particularly coal, are the largest source of
energy used for electricity generation.
Decreasing the use of fossil fuels to generate electricity, as well as decreasing electricity consumption, would
reduce greenhouse gas emissions.
Electricity conservation and efficiency
The Energy Star program rates electric appliances on how well they con- serve energy so that consumers can buy
the most efficient models. Examples of the Energy Star program include efficient refrigerators, com- pact
fluorescent lighting, and efficient construction of new homes. Individuals can choose to do without some
electrical appliances.
Renewable, low-carbon, or carbon-free sources of electricity
Renewable or alternate energy sources such as hydropower, geothermal, or wind power can reduce the amount of
fossil fuels used and reduce green- house gas emissions.
However, the materials used and the environmental impacts of these technologies must also be accounted for.
Transportation is the second largest source of greenhouse gases in the United States
With 220 million automobiles, Americans travel 2 trillion miles each year; 33% of cities are devoted to cars (e.g.,
roads, parking lots, etc.); and the U.S. government spends $200 million per day on road construction and repaIr.
There are substitutes for our inefficient automobiles
Modern cars are highly inefficient and waste up to 85% of the fuel
burned; only about 15% of the fuel used actually moves the automobile down the road.
Fossil-fuel emissions from cars can be cut by: (1) making cities more friendly to pedestrian and bicycle traffic; (2)
advancing technology such as hybrid vehicles, which use both electricity and gasoline-powered engines; and (3)
using alternative fuels such as biodiesel.
Public policy and personal transportation choices
Increasing use of public transportation is the single most effective strategy for conserving energy and reducing
pollution.
If 10% of U.S. residents used public transportation, the enormous energy savings could drastically reduce our
dependence on foreign oil and the nation's contribution to global climate change.
Although mass transit ridership has increased, reliable and convenient public transport is not available in many
U.S. communities.
Beyond technology and personal choice, international climate treaties also play a role
In 1992, the United Nations convened the United Nations Conference on Environment and Development Earth
Summit in Rio de Janeiro.
At the Summit, nations signed the Framework Convention on Climate Change (FCCC), which outlined a plan for
reducing greenhouse gas emissions to 1990 levels by the year 2000 through a voluntary approach.
However, voluntary reductions do not always work; while Germany and the United Kingdom cut their emissions,
the United States increased its emissions by 12% between 1990 and 2000.
Developing nations initiated an effort to require all signatory nations to reduce their greenhouse gas emissions;
this effort led to the development of the Kyoto Protocol.
The United States has resisted the Kyoto Protocol
The Kyoto Protocol (1997) is a binding international treaty that requires all nations to reduce their greenhouse gas
emissions by 2012.
The United States has called the treaty unfair because it requires developed, but not developing, nations to reduce
emissions.
Developing nations maintain that it is the developed world that created the problem, so developed nations should
make the sacrifices.
Under this treaty, carbon dioxide emissions would still increase, but much more slowly than currently.
The Kyoto Protocol has been ratified by III nations, and is waiting on ratification by Russia to take effect.
Some feel that climate change demands the precautionary principle
According to the precautionary principle, a lack of scientific certainty
should not prevent or postpone taking cost-effective measures to protect the environment.