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Global Warming

Note: EPA no longer updates this information, but it may be useful as a reference or resource.

Please see www.epa.gov/airtrends for the latest information on Air Quality Trends.

Nature and Sources: The Earth's climate is fueled by the Sun. Most of the Sun's energy, called solar radiation, is absorbed by the Earth, but some is reflected back into space. A natural layer of atmospheric gases absorbs a portion of this reflected solar radiation, eventually releasing some of it into space, but forcing much of it back to Earth. There it warms the Earth's surface creating what is known as the natural "greenhouse effect," as illustrated in the diagram below. Without the natural greenhouse effect, the Earth's average temperature would be much colder, and the planet would be covered with ice.

The greenhouse effect is being accelerated by releases of certain

gases to the atmosphere that are causing the Earth's temperature to


Recent scientific evidence shows that the greenhouse effect is being increased by release of certain gases to the atmosphere that cause the Earth's temperature to rise. This is called "global warming." Carbon dioxide (CO2) accounts for about 85 percent of greenhouse gases released in the U.S. Carbon dioxide emissions are largely due to the combustion of fossil fuels in electric power generation. Methane (CH4) emissions, which result from agricultural activities, landfills, and other sources, are the second largest contributor to greenhouse gases in the U.S.

Industrial processes such as foam production, refrigeration, dry cleaning, chemical manufacturing, and semiconductor manufacturing produce other greenhouse gas emissions such as hydrofluorocarbons (HFCs). Smelting of aluminum produces another greenhouse gas called perfluorinated compounds (PFCs). Emissions of NOx and VOC from automobile exhaust and industrial processes contribute to the formation of ground-level ozone or smog, also a greenhouse gas.

Health and Environmental Effects: Greenhouse gas emissions could cause a 1.8 to 6.3 Fahrenheit rise in temperature during the next century, if atmospheric levels are not reduced. Although this change may appear small, it could produce extreme weather events, such as droughts and floods; threaten coastal resources and wetlands by raising sea level; and increase the risk of certain diseases by producing new breeding sites for pests and pathogens. Agricultural regions and woodlands are also susceptible to changes in climate that could result in increased insect populations and plant disease. This degradation of natural ecosystems could lead to reduced biological diversity.

International Developments: In 1988, the Intergovernmental Panel on Climate Change (IPCC) was formed to (1) assess available scientific information on climate change; (2) assess environmental and socioeconomic impacts of climate change; and (3) formulate response strategies. In 1992, 150 countries signed a treaty known as the "Framework Convention on Climate Change" (FCCC) to stabilize the concentration of greenhouse gases in the atmosphere. Early indications suggest that most industrialized countries are not on track to meet the year 2000 target for reducing emissions of greenhouse gases, and further, that holding emissions at 1990 levels will not prevent or solve the problem. At a conference held in December 1-11, in Kyoto, Japan, the Parties to the FCCC agreed to binding greenhouse gas emission targets for industrialized countries for the period of 2008-2012 and the market-based measures, such as international emissions trading, for meeting those targets. The average reduction target for all industrialized countries for this period is 5.2% below 1990 emission levels.

U.S. Programs to Mitigate Climate Change: The United States adopted a Climate Change Action Plan (CCAP) in 1993 to reduce greenhouse gas emissions. Hundreds of companies and nonprofit organizations are working together to effectively reduce their emissions. The Plan involves 50 programs implemented by EPA, the Department of Energy, the Department of Agriculture, and other Government agencies. EPA's voluntary pollution prevention programs seek to prevent greenhouse gas emissions through partnerships with business, government, and other groups by stimulating investments in energy-efficient technology and practices. Combined, EPA's voluntary pollution prevention programs to reduce greenhouse gas emissions have over 2,000 partners. By the year 2000, CCAP is expected to achieve annual reductions of 76 million metric tons (MMT) of carbon equivalent greenhouse gas emissions.

Recent Trends in US Greenhouse Gas Emissions: 1990-1996

(MMTs of Carbon Equivalent)*

Gases and Sources 1990 1991 1992 1993 1994 1996
Carbon Dioxide (CO2 ) 1,353 1,320 1,340 1,370 1,391 1,305
Forests (sink) (125) (123) (122) (120) (119) (117)
Methane (CH4) 170 172 173 171 176 177
Nitrous Oxide (N2O) 36 37 37 38 39 40
Hydrofluorocarbons (HFCs) 12 12 13 14 17 21
Perflourocarbons (PFCs) 5 5 5 5 7 8
Sulfur Hexafluoride (SF6 ) 7 7 8 8 8 8
Net US Emissions 1,458 1,447 1,470 1,504 1,538 1,559

Note: The totals presented in the summary table may not equal the sum of the individual categories due to rounding.

*Source: Climate Action Report: 1997 Submission of the United States of America Under the United Nations Framework Convention on Climate Change, Department of State Publication 10496, July 1997.


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