The topic of global warming inspires heated debates among world leaders, industry representatives, and environmentalists. While there is a strong consensus in the scientific community that the greenhouse effect is a real phenomenon, and that humans are adding to concentrations of greenhouse gases in the atmosphere, much remains unknown about the long-term consequences of anthropogenic activity on the climate.

Greenhouse gases--water vapor, carbon dioxide, nitrous oxide, methane, chlorofluorocarbons¹, and ozone--trap heat in the atmosphere instead of allowing it to radiate back into space, the way glass traps heat in a greenhouse. Except for chlorofluorocarbons, greenhouse gases are natural components of the atmosphere, and the greenhouse effect itself is a natural phenomenon. Without it, the earth would be about 60 degrees cooler than it is today, and life as we know it would be impossible.²

However, human activities are increasing the levels of these gases in the atmosphere, causing an 'enhanced greenhouse effect' that traps more heat. There is evidence that climate warming is already underway. The Intergovernmental Panel on Climate Change, a United Nations Task Force examining the plausibility of human-induced climate change, has reported "a discernable human influence" on climate.³ The U.S. Environmental Protection Agency reported that the twentieth century was the hottest in the last thousand years, that the nine hottest years on record have all occurred since 1987, and that 1998 was the hottest year ever.⁴

No one knows how much the climate will change, how much the human contribution to greenhouse gases will affect it, or what the long-term effects of global warming will be on ecosystems, species distribution, and our own civilization. Scientists' estimates of the total amount of surface warming that will occur during the next century, averaged over the whole globe, range from 1.8 to 6.3 degrees Fahrenheit. (In comparison, the global average temperature change in 1816, the infamous "Year Without a Summer" when crops failed around the world and New England farmers experienced frost in July, was a drop of less than 1 degree Fahrenheit.)⁵

Not all regions will experience equal warming. Some areas may become much hotter and drier, while others actually experience colder weather. Other predicted effects of global warming include melting of the polar ice caps, flooding of coastlines, severe storms, changes in precipitation patterns, and widespread changes in the existing ecological balance. Current models predict a rise in global sea levels of 15-95 centimeters over the next century, high enough to put the homes of a third of the world's population underwater.⁶ Infectious diseases may increase due to an expansion of habitat for disease vectors like mosquitoes. Many species may be unable to adapt to such swift changes in the climate, and may become extinct.⁷

Humans enhance the greenhouse effect primarily by burning fossil fuels (coal, oil and natural gas). These fuels are stored carbon, formed millions of years ago from organic matter. Burning them returns the carbon to the atmosphere in the form of carbon dioxide, the gas that contributes most to the enhanced greenhouse effect. Each year, fossil fuel use adds an estimated 5.5 GtC (gigatons of carbon) to the atmosphere.⁸

Land use, particularly deforestation, also contributes to the accumulation of greenhouse gases in the atmosphere. Cutting down and burning forests not only releases carbon dioxide, but also reduces an important carbon storage reservoir, so that less carbon can be absorbed from the atmosphere. Deforestation and agricultural techniques add about 2.0 GtC to the atmosphere each year.⁸

Other natural processes like plant respiration, sea-surface exchange of gases, and natural decay of residue also give off carbon dioxide, while plant photosynthesis and the oceans absorb it from the atmosphere. Each year, natural processes add and remove about the same amount of carbon from the atmosphere, about 102 GtC.

The amount of carbon in the atmosphere has changed noticeably in the past 150 years. It has increased from 280 ppmv (parts per million by volume) at the time of the Industrial Revolution, to 367 ppmv today, an increase of 30%. Nearly all scientists believe that this increase is a result of human contributions.⁴

Other greenhouse gases are less common than carbon dioxide in the atmosphere, but have more potent effects. Nitrous oxide, for example, is only one-thousandth as common as carbon dioxide, but is 200-300 times as effective at trapping heat, and remains in the atmosphere far longer than carbon dioxide. Chlorofluorocarbons, which were not present in the atmosphere at all prior to the Industrial Revolution, have warming effects ranging from 3,000 to 13,000 times that of carbon dioxide, and persist for up to 400 years.

Built into this system is a long "lag" time; even if all human contributions to the greenhouse effect were to cease entirely, the atmosphere would return to "natural" pre-industrial levels only very slowly, by a few ppmv every 50 years.⁸

Putting the brakes on global warming is no easy matter. Some ways to reduce our contribution of greenhouse gases include setting strict emissions standards, reducing our fossil fuel use, developing alternative sources of energy to replace fossil fuels, removing carbon dioxide from emissions at the source, eliminating the use of chlorofluorocarbons, slowing or mitigating deforestation, and developing agricultural techniques that release less carbon dioxide to the atmosphere.

These changes would have far-reaching impacts on our current use of energy, affecting industries and the economy. Some point out that developing new technologies to reduce our dependence on fossil fuels could spur economic growth, but critics contend that the costs of implementing an effective program would be too high.

The most recent international effort to address the greenhouse effect was the Kyoto Protocol, an agreement among the industrialized nations of the world to reduce emissions of six greenhouse gases over a certain period of time. More than 170 nations signed the treaty, including the U.S., the European Union, Canada, and Japan. If the treaty had been ratified by the U.S. Congress, it would have required the U.S. to reduce emissions of greenhouse gases by 7% below 1990 levels, from 2008-2012. The Congressional Research Service Report, Global Climate Change: Reducing Greenhouse Gases - How Much From What Baseline (1998) describes the Kyoto Protocol, particularly the energy, economic, and carbon sequestration variables associated with its implementation in the U.S.

Critics of the Kyoto Protocol focused on the fact that it levied restrictions only on the developed nations of the world, and not on developing countries like China, India, and Brazil. There were also disagreements over whether a country was allowed to establish carbon sinks instead of reducing emissions or whether emissions reduction was an absolute requirement, whether a country could claim carbon credits if it helped a developing country reduce emissions, which land use changes counted as establishment of a carbon sink, and how to enforce the Protocol and penalize noncompliant countries.

In late March 2001, President Bush announced that the U.S. would withdraw from the Kyoto Protocol. In the absence of ratification, the treaty is not considered legally binding. The CRS Issue Report, Global Climate Change: The Kyoto Protocol (2001) describes the political negotiations that occurred from the drafting of the Protocol in 1997 to its current-day rejection by the U.S., while the CRS Report, Global Climate Change: Selected Legal Questions About the Kyoto Protocol (2001) explains the legal implications of signing, but not ratifying, the Protocol.

Bush suggested in his June 11, 2001 remarks that instead of committing to the Kyoto Protocol standards, the U.S. would combat global warming in other ways. In a Climate Change Review issued the same day, he listed development of energy-efficient technology, market-based incentives to encourage industries to reduce greenhouse gas emissions on their own, and conservation programs that help sequester carbon in the soil, as actions the U.S. would take.

Initially, the U.S. withdrawal from the Kyoto Protocol was considered its death knell. The agreement can only enter into force internationally if it is ratified by at least 55 nations that, together, accounted for at least 55% of the total carbon dioxide emissions in 1990. Given that the U.S. alone was responsible for about 25% of the 1990 carbon dioxide emissions, experts predicted that without the participation of the U.S., the Kyoto Protocol would never be implemented.⁹

However, in July 2001, the European Union, Japan, Canada, Russia, Australia, and 170 other nations reached an agreement to proceed with the treaty. In order to secure the support of highly industrialized nations, the European Union was forced to make substantial concessions. The targets for emissions reduction were reduced by two-thirds from the original goals, and countries were given the option of planting carbon-absorbing forests to earn pollution credits, in lieu of reducing emissions.¹⁰

The European Union and other nations continue to pressure Bush to adopt the Kyoto Protocol. The Senate Foreign Relations Committee has passed a unanimous resolution calling for him either to sign on to a revised version of the Kyoto Protocol, or to develop a new international agreement for reducing greenhouse gases.¹¹

Written by Heather E. Lindsay.

Footnotes:

2. National Safety Council's Environmental Health Center http://www.nsc.org/ehc/climate/ccucla4.htm.

3. Intergovernmental Panel on Climate Change http://www.ipcc.ch/pub/sarsum1.htm#four.

4. Environmental Protection Agency http://www.epa.gov/globalwarming/faq/fundamentals.html#q2.

5. The Woods Hole Research Center http://www.whrc.org/globalwarming/warmingearth.htm.

6. Miller, G. Tyler. Living in the Environment: Principles, Connections, and Solutions. Eleventh Edition. Brooks/Cole Publishing Company, 2001.

7. Natural Resources Defense Council http://www.nrdc.org/globalWarming/fcons.asp.

8. National Safety Council's Environmental Health Center http://safety.webfirst.com/public/ehc/climate/chaptr3.pdf.

9. U.S. Department of State http://usinfo.state.gov/admin/005/wwwh1a05.html.

10, 11. The Washington Post newspaper http://www.washingtonpost.com/wp-dyn/articles/A56052-2001Jul26.html
http://www.washingtonpost.com/wp-dyn/articles/A19468-2001Aug1.html

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