United States
                         Environmental Protection
                   Office of Policy,
                   Planning, and
         May 1992
                         Climate  Change
                         Discussion  Series
                   Global Climate Change
The "greenhouse effect" is a natu-
rally occurring phenomena. So called
"greenhouse" gases act to warm the
earth by absorbing infrared radia-
tion that is given off from the earth's
surface after sunlight strikes it.

The term "global warming" refers to
an enhanced greenhouse effect re-
sulting from human activities. Since
the beginning of the industrial revo-
lution, human activities have led to
increased atmospheric concentra-
tions of greenhouse gases such as
nitrous oxide (N2O), and chlorofluo-
rocarbons (CFCs). Fossil fuel burn-
ing, which releases COz,  CO, N2O,
and other pollutants, has increased at
a rapid  rate over the last century.
More cattle and greater use of fertil-
izer have led to increased emissions
of CH*  and N2O.  Deforestation in
many areas of the globe, has contrib-
uted to increased CO2 concentrations.
Atmospheric concentrations of CFCs
and tropospheric ozone have also in-
creased, primarily because of indus-
trial activity.

The earth's atmosphere has under-
gone many cycles of warming and
cooling in the past. However, two
   Gases Trap the Earth's Heat
aspects of current greenhouse wann-
ing predictions differ from climate
changes in the recent past First, the
average 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 comparable magnitude have oc-
curred over thousands of years and
have allowed for gradual ecosystem
adjustments. We may now experi-
ence similar changes during the next
century  at a rate faster than many
ecosystems can adapt

A1990 study by the Intergovernmen-
tal Panel on Climate Change (IPCC),
involving several hundred scientists,
concluded that a doubling of CO2
levels would most likely lead to a 1.5°
to 4.5°C (3° to 8°F) warming of the
earth in the next 100 years. An in-
crease in all greenhouse gases equiva-
lent to CO2 doubling could occur as
early as 2030.
  Major Greenhouse Gases
  Carbon Dioxide (COZ): Currently responsible for approxi-
  mately 1/2-2/3* of humans' contribution to global warm-
  ing, CO/s atmospheric concentration has risen 25 percent
  since the beginning of the Industrial Revolution. Combus-
  tion of fossil fuels and deforestation are the main sources of
  this increase. Because society's basic energy sources pro-
  duce CO2, its atmospheric concentration is projected to
  continue to increase unless strong measures are taken to
  enrourage energy conservation,alternanveenergy sources,
  and forest preservation.
  Methane (Oft): Although methane has a much lower
  atmospheric concentration than COj, 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, CH, concen-
  trations may be the easiest to stabilize with modest cuts in
  Chlorofluorocarbons (CFCs): Invented in this century,
  CFCs have been implicated not only in chemical destruc-
  tion of stratospheric O2»ne, but also in greenhouse warm-
               ing. Each CFC molecule has a direct warming effect several
               thousand times that of a COj molecule. However, CFCs cause
               an indirect cooling effect by destroying ozone, another green-
               house gas. The extent to which me direct warming effect is
               onset by me indirect ooolmgeffect has not yet beendetermined.
               CFCs are used in refrigerants, aerosol propellants, foam-blow-
               ing agents, and solvents. Their atmospheric concentration is
               increasingatarateof 4percentperyear. Substitutes are being
               developed that are not  as chemically stable and that
               therefore will not accumulate as fast in the atmosphere.
               The Montreal Protocol, an international agreement, and recent
               U.S. measures currently limit production of these gases, but
               further limits may be necessary.
               Nitrous Oxide (N2O): Nitrous oxide's concentration in the
               atmosphere is increasing atthe rate of 0.25 percent per year.
               Although nitrous oxide is a more potent greenhouse gas
               than C(\ its contribution to global warming is lower be-
               cause of its low concentration. Anthropogenic sources in-
               clude fossil fuel and biomass combustion, agricultural
               fertilizers, and land disturbances. The relative contribution
               of natural and anthropogenic (human) sources of N2O are
               not that well understood.
 •Based on 1990 emiuion estimate* and IPCC 1992 GWPS.CH. I
NOTE: Climate change refers to potential modification of the earth's climate resulting from increasing atmospheric concentrations of greenhouse gases such as carbon
dioxide (CO,). methane (CH4), nitrous oxide (N ,O), and Chlorofluorocarbons (CFCs). Through a naturally occurring process known as die "greenhouse effect," these
gases act to warm the earth by trapping heat in the atmosphere. This process plays an important rote in maintaining the 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.
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                 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 re-
quire costiy 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 de-
mands will likely increase in many regions.
       Biodiversity: Ranges and populations of various spe-
       desccodd be reduced. Some speties 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: Summer mortality could increase, while winter
       mortality could decrease to a lesser extent. Regional
       disease patterns could also change.
             Options to Reduce
       Greenhouse Gas Emissions

    Increase energy efficiency and use of renew-
    able energy sources.
     - Strengthen building and appliance efficiency
     - Encourage utilities to invest in conservation mea-
      sures to reduce demand.
     - Promote renewable energy sources, such as solar,
      wind, hydro and geothermal power.
     - Encourage transportation efficiency and alter-
      native fuels.
     - Adopt carbon or fossil fuel taxes.
    Accelerate phase-out of CFCs.
    Capture methane and recover energy from the
    various methane sources.
    Reduce deforestation and encourage tree plant-
    ing programs.
    Reduce N2O emissions from fertilizer use and
    other sources.
    (See Energy, Transportation, Agriculture, and For-
    estry Discussion Sheets).
          Options to Adapt Climate 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
            specialized crop and livestock varieties; prepare for
            the potential introduction of new pests; improve
            irrigation efficiency; increase the use of conserva-
            tion tillage and crop rotation practices.
            Water Resources: Conserve; protect water quality
            and opportunities for future supplies; improve riv-
            er basin and drought contingency planning.
            Forests: Maintain diversity and extensiveness; pre-
            pare  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; im-
            prove disease surveillance systems.
            (See Adaptation, Sea Level Rise, Forestry, Biodiver-
            sity, and Agriculture Discussion Sheets).
Based on EPA's Report to Congress, The Potential Effects of Global Climate Change on the United Slates, Washington, DC, 1989; EPA's
Report to Congress, Policy Options for Stabilizing Global Climate, Washington, DC, 1990; EPA's Adapting to Climate Change: What
Governments Can Do,  Washington, DC, 1991; IPCC's Policymakers' Summaries, 1990; and the Selected Summary of Current State
Responses to Climate Change, Washington, DC, 1990.

EPA's Climate Change Outreach Program is designed to raise awareness about climate change and provide assistance to state and local
governments, industry, and non-governmental organizations in the evaluation of cost-effective response strategies. For further information
about this program, please contact Joel Smith at 202/260-8825.
             U.S. EPA Climaft Change DiscuMion Series W2

                Global Climate Change Sea Level Rise
                Adaptation to       Transportation
                 Climate Change    Energy
                Forestry          Water Resources
                Agriculture        Biodiversity
        Office of Policy Analysis
        Climate Change Division (PM221)
        401 M Street, SW.
        Washington, DC 20460