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In contrast to the scientific consensus, there is a counterargument by a few individual scientists who cast doubt on the global warming forecast. Their claims are based on the blocking effect on solar radiation caused by aerosols. Aerosols are particles of solids and liquids suspended in the atmosphere that backscatter incoming solar radiation. Aerosols are produced from both natural sources such as volcanoes, and pollution sources such as forest fires and urban emissions. They occur in both primary and secondary forms, meaning that some enter as particles, whereas others develop into particles from gaseous pollutants. In addition, pollutants increase condensation and cloud formation, thereby increasing reflection of solar radiation. Because aerosols and clouds reduce solar radiation receipt in the lower atmosphere and at the Earth's surface, they also reduce solar heating and may cause temperatures to decline as a result.

The effect of aerosols on solar heating of the lower atmosphere was dramatically demonstrated in the hours immediately after 9/11. The U.S. government ordered grounding of all aircraft, and for a short time, skies over the United States and Canada were clear of condensation trails from high-flying jetliners. During that time, a distinct rise in surface temperature was recorded over broad areas.

With the resumption of flying, temperatures fell back to pre-9/11 levels. With the dramatic increase in global air pollution in this century, the atmosphere has grown dirtier and less transparent to solar radiation. Less solar energy reaches the Earth's surface, and if there were no counterbalancing factors, the lower atmosphere would probably be growing cooler. But there are counterfac-tors in the form of CO2 and warming gases.

effects of global warming

If global warming proceeds, Earth's equilibrium surface temperature will rise 3-11 degrees F (2-6 degrees C) over the next 100 years. Earth's equilibrium surface temperature will reach 62-68 degrees F (17-20 degrees C). This means that more thermal energy will be available to drive atmospheric processes such as winds, air mass movement, and evaporation. How all of this will interrelate to shape the broad picture of global climate is difficult to forecast. Based on computer simulation models illustrating anticipated changes in atmospheric circulation, scientists forecast that warming will not be geographically uniform; in some regions it will be significantly greater than others, and the climatic changes will likely be different in different parts of the world.

Specific examples of the modeling approach for change of global temperature scenarios are simple climate models (SCMs). SCMs are the simplified models used by the Intergovernmental Panel on Climate Change (IPCC) to provide projections of the atmospheric concentrations of greenhouse gases, global mean temperature, and sea-level change response, using as input emissions scenarios describing the future developments in the emissions of greenhouse gases.

The increased heat content of the troposphere will strengthen certain air masses, increasing their moisture content, leading to greater storminess in some regions. It is already known that that storminess and precipitation on the Pacific coast of the Americas increases substantially with only 1.8-3.6 degrees F (1-2 degrees C) of atmospheric warming associated with El NiƱo, the periodic buildup of warm water in the east Pacific near the equator. Increased ocean temperatures may also lead to increased magnitude and frequency of hurricanes. Hurricanes are driven by the energy of water vapor, called latent heat. Warmer ocean waters supply more vapor, and thus more energy, to the atmosphere to fuel storms. Hurricanes are the most powerful storms on the planet, and the greater their fuel supply, the bigger and more destructive they are.

Although it is difficult to connect specific weather events to global warming, an increase in global temperatures may, in turn, cause other changes, including glacial retreat 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 frequency and intensity of extreme weather events. Other effects may include changes in agricultural yields, reduced summer stream flows, 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.

The broad agreement among climate scientists that global temperatures will continue to increase has led nations, states, corporations, and individuals to implement actions to try to curtail global warming or adjust to it. Many environmental groups encourage action against global warming, often by the consumer, but also by community and regional organizations. There has also been business action on climate change, including efforts at increased energy efficiency, and moves to alternative fuels. One important innovation has been the development of greenhouse gas emissions trading through which companies, in conjunction with government, agree to cap their emissions or to purchase credits from those below their allowances.

the kyoto protocol

The world's primary international agreement on combating global warming is the Kyoto Protocol, an amendment to the United Nations Framework Convention on Climate Change (UNFCCC), negotiated in 1997. The protocol now covers more than 160

countries and over 55 percent of global greenhouse gas emissions. As of 2007, the United States (historically the world's largest greenhouse gas emitter), Australia, and Kazakhstan had not ratified the treaty. China and India have ratified the treaty, but as developing countries, are exempt from its provisions. This treaty expires in 2012, and international talks began in May 2007 on a treaty to succeed the current one. Increased awareness of the scientific findings surrounding global warming has resulted in political and economic debate. Poor regions, particularly in Africa, appear at greatest risk from the suggested effects of global warming, while their actual emissions have been negligible compared to the developed world.

At the same time, developing country exemptions from provisions of the Kyoto Protocol have been criticized by the United States and Australia, and have been used as part of their rationale for continued non-ratification. China's CO2 emissions, mainly from automobiles and coal power plants, are expected to exceed those of the United States within the next few years. China has contended that it has less obligation to reduce emissions, since its emissions per capita are about one-fifth those of the United States. The United States contends that if they must bear the costs of reducing emissions, so should China. India will also soon be one of the biggest sources of industrial emissions, and has made assertions similar to China's on this issue.

The world's primary body for crafting a response is the Intergovernmental Panel on Climate Change (IPCC), a UN-sponsored activity that holds periodic meetings between national delegations on the problems of global warming, and issues working papers and assessments on the current status of the science of climate change, impacts, and mitigation.

SEE ALSO: Carbon Emissions; Carbon Sinks; Evaporation Feedbacks; Greenhouse Effect; Greenhouse Gases; Hurricanes and Typhoons; Kyoto Protocol.

BIBLIOGRAPHY. David Archer, Global Warming: Understanding the Forecast (Blackwell Publishing, 2007); Intergovernmental Panel on Climate Change (IPCC), Climate Change 2007: The Physical Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge University Press, 2007); S.F. Singer and D.T. Avery, Unstoppable Global Warming: Every 1,500 Years (Rowman and Little-

field Publishers, 2007); M.E. Williams, Global Warming: An Opposing Viewpoints Guide (Greenhaven Press, 2006).

Jun-Ki Choi Bhavik R. Bakshi Ohio State University

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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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