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
------- |