United States Environmental Protection Agency Policy, Planning, And Evaluation (2122) EPA 230-F-95-002 April 1995 &EPA Climate Change Discussion Series Global Climate Change The greenhouse effect is a naturally occurring phenomenon. So called greenhouse gases act to warm the earth by absorbing infrared radiation that is given off from the earth's surface after sunlight strikes it. The term global warming refers to an enhanced greenhouse effect resulting from human activities. Since the begin- ning of the industrial revolution, human activities have led to increased atmo- spheric concentrations of greenhouse gases such as carbon dioxide (CO,), methane (CH4), nitrous oxide (N20), and chlorofluorocarbons (CFCs). Fossil fuel burning, which releases CO2, CO, N20 and other pollutants, has increased at a rapid rate over the last century. More cattle and greater use of fertilizer have led to increased emissions of CH4 and N20. Deforestation in many areas of the globe has contributed to increased CO2 concentrations. Atmospheric concentrations of CFCs and tropospheric ozone have also in- creased, primarily because of industrial activity. The Earth's atmosphere has undergone many cycles of warming and cooling in the past. However, two aspects of current greenhouse warming predictions differ from climate changes in the recent past. First, the temperature of the earth is expected to rise higher than the planet has experienced in the last 125,000 years. Second, past climate changes of compa- rable magnitude have occurred over thousands of years and have allowed for gradual ecosystem adjustments. We may now experience similar changes during the next century at a rate faster than many ecosystems can adapt. A 1990 study by the Intergovernmental Panel on Climate Change (IPCC), involving several hundred scientists, concluded that a doubling of CO2 levels would most like likely lead to a 1.5 to 4.5 degrees C (3 to 8 degrees F) warming of the earth in the next 100 years. An increase in all greenhouse gases equivalent to a doubling of CO, emissions could occur as early as 2030. Major Greenhouse Gases Carbon Dioxide (CO,): Currently responsible for approxi- mately half to two-thirds* of humans' contribution to global warming, CO2's atmospheric concentration has risen 25 percent since the beginning of the Industrial Revolution. Combustion of fossil fuels and deforestation are the main sources of this increase. Because society's basic energy sources produce CO2, its atmospheric concentration is projected to continue to increase unless strong measures are taken to encourage energy conservation, alternative energy sources, and forest preservation. Methane (CH4): Although methane has a much lower atmospheric concentration than CO2, it is a more potent greenhouse gas and its concentration is increasing at a rate of 1 percent per year. Sources include rice paddies, cows, termites, natural gas leakage, biomass burning, landfills, and wetlands. Of the major greenhouse gases, CH4 concentrations may be the easiest to stabilize with modest cuts hi emis- sions. Chlorofluorocarbons (CFCs): Invented hi this century, CFCs have been implicated not only in chemical destruction of * Based on 1990 emission estimates and IFCC 1992 GWPs (global wanning potential). CH4 estimates include indirect effects. stratospheric ozone, but also in greenhouse wanning. Each CFC molecule has a direct wanning effect several thousand times that of a CO2 molecule. However, CFCs cause an indirect cooling effect by destroying ozone, another green- house gas. The extent to which the direct wanning effect is offset by the indirect cooling effect has not yet been deter- mined. CFCs are used in refrigerants, aerosol propellents, foam-blowing agents, and solvents. Their atmospheric concentration is increasing at a rate of 4 percent per year. Substitutes are being developed that are not as chemically stable and that therefore will not accumulate as fast hi the atmosphere. The Montreal Protocol, an international agree- ment, and recent U.S. measures currently limit production of these gases, but further limits may be necessary. Nitrous Oxide (N20): Nitrous oxide's concentration in the atmosphere is increasing at a rate of 0.25 percent per year. Although nitrous oxide is a more potent greenhouse gas than CO2, its contribution to global warming is lower because of its low concentration. Anthropogenic (human) sources include fossil fuel and biomass combustion, agricultural fertilizers, and land disturbances. The relative contribution of natural and anthropogenic sources of N20 are not that well understood. NOTE: Climate Change refers to potential modification of the earth's climate resulting from increasing atmospheric concentrations of greenhouse eases such as carbon dioxide (CO2), methane (CH ), nitrous oxide (N,0), and chlorofluorocarbons (CFCs). Through a naturally occurring process known as the ogreenhouse effect.o these gases act to warm the earth by trapping heat in the atmosphere. This process plays an important role in maintaining earth's current temperature and climate. By increasing concentrations of greenhouse gases, human activities are trapping more heat in the atmosphere and potentially changing the earth's climate. ------- Potential Impacts of Climate Change on the United States Coastal Resources: Sea level rise could cause loss of wetlands and drylands along coastlines and could require costly measures to protect developed areas. Water Resources: Changes in water flow and water quality could occur with the potential for more severe water shortages in some areas. Agriculture: Yields could change (productivity could shift northward) and the range of agricultural pests and diseases could also move northward. Irrigation demands will likely increase in many regions. Biodiversity: Ranges and populations of various species could be reduced. Some species could become extinct. Electricity Demand: Electricity demand could rise in all but the northernmost regions of the United States as the use of air conditioning increases to compensate for higher temperatures. Air Quality: Higher temperatures could increase air pollution in some regions. Health: In addition to likely increases in heat-related deaths, the spread of insect-borne infectious diseases such as malaria and dengue fever could extend northward. Options to Reduce Greenhouse Gas Emissions • Increase energy efficiency and use of renewable energy sources. Strengthen building and appliance efficiency standards. Encourage utilities to invest in conservation measures to reduce demand. Promote renewable energy sources, such as solar, wind, hydro, and geothermal power. Encourage transportation efficiency and alternative fuels. Adopt carbon or fossil fuel taxes. Accelerate phase-out of CFCs. Capture methane and recover energy from the various • mnthano sources. Reduce deforestation and encourage tree planting • programs. Reduce N,0 emissions from fertilizer use and other • sources. to Adapt to Change Sea Level Rise: Establish buffer zones to allow for inland migration of wetlands and to limit loss of structures; incorporate sea level rise into coastal management plans. Agriculture: Maintain genetic diversity; develop special- ized crop and livestock varieties; prepare for the potential introduction of new pests; improve irrigation efficiency; increase the use of conservation tillage and crop rotation practices. Water Resources: Conserve; protect water quality and opportunities for future supplies; improve river basin and drought contingency planning. Forests: Maintain diversity and extensiveness; prepare for episodes of increased mortality due to changes in fire and pest disturbances. Natural Systems: Maintain species ranges; avoid barriers to migration and habitat fragmentation; establish migratory pathways. Health: Recognize health^debilitating weather; improve disease surveillance systems. Based on EPA's Report to Congress, The Potential Effects of Global Climate Change on the United States, Washington, B.C., 1989; EPA's Report to Congress, Policy'Options for Stabilizing Global Climate, Washington, D.C., 1990; EPA's Adapting to Climate Change: What Governments Can Do, Washington, D.C., 1991; IPCC's FWicymakers' Summaries, 1990; and the Selected Summary of Current State Responses to Climate Change, Washington, D.C., 1990. EPA's State and Local Climate Change Outreach Program is designed to raise awareness about climate change and provide technical and financial support to state and local agencies and non-profit organizations in the analysis and development of cost-effective response strategies.. For further information, contact Kitty Sibold at 202-260-8825. Order additional sheets from the Climate Change Discussion Series: U.S. EPA, Climate Change Division (PM221), 401 M Street, SW, Washington, D.C. 20460, fax: 202-260-6405 ------- |