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Understanding Carbon Dioxide (CO2):
Future Trends in Emissions and Emissions Control
Understanding CO2
At the heart of the global climate change issue is the concern that increasing levels of greenhouse
gases in the atmosphere could cause an enhanced greenhouse effect (a warming of the global
climate beyond what might occur naturally) or "global warming." Scientists are monitoring
carbon dioxide (CO2) and several other greenhouse gases to determine their roles in the
greenhouse effect. Water vapor (which is responsible for most of natural greenhouse warming),
methane, CFCs and nitrous oxide are the other significant greenhouse gases.
Carbon dioxide is not a pollutant. It is a by-product of human, plant and animal respiration, a
product of combustion, and a vital component of photosynthesis. Of the CO2 that is emitted as a
result of human activities, about half remains in the atmosphere, while the other half is removed
by "sinks," which naturally absorb CO2. Sinks for CO2 include the ocean, soils and vegetation.
Currently, our understanding of these sinks is limited, adding to the uncertainties surrounding
predictions of the climate impact of rising CO2 emissions.
Some scientists believe that man-made emissions of carbon dioxide are significant enough to
cause an enhanced greenhouse effect. However, atmospheric water vapor and clouds play a far
more active role in affecting climate change, and scientists agree that much more research is
needed on the atmospheric interactions of clouds and oceans. Even so, CO2 has been the primary
target of efforts to reduce greenhouse gas emissions. Such efforts include proposed emissions
limits, targets and timetables for reductions, and taxes on carbon or other energy sources.
Historical and Future Trends
Understanding the historical data on CO2 emissions provides clues to determining whether there
is a relationship between increased atmospheric CO2 levels and observed changes in global mean
surface temperature. The computer models that have been used to simulate the relationship of
CO2 and climate change are still evolving and do not fully agree or explain all of the observational
evidence now available (e.g., from satellites and Arctic temperature data).
Carbon dioxide levels have varied widely during the Earth's history. Since the mid-1700s,
atmospheric concentrations of CO2 have risen 25 percent. This increase is largely a result of
industrialization, the increased burning of fossil fuels as populations grow, and increases in living
standards. The greatest increases in CO2 emissions occurred after World War II. For example,

 between 1950 and 1988, the United States annual CO2 output roughly doubled. Interestingly,
most of the observed increase in global mean temperatures occurred before 1940, (i.e., before
significant increases in manmade CO2 emissions).
Many forecasters agree that greenhouse gas levels could double sometime in the next century as a
result of a number of factors, including: population growth, increased use of fossil fuels and
increased economic activity in developing countries Yet scientists disagree on whether the
increased atmospheric concentrations of CO2 will cause any significant climate change.
Future Sources of Increased CO2 Emissions
According to the International Energy Agency, as much as 85 percent of the projected increase in
manmade global CO2 emissions will come from developing countries and countries with
economies in transition (e.g., Eastern European nations). In fact, the U.S. contribution of
manmade CO2 is less than 22 percent of total CO2 emissions worldwide and has significantly
declined over the past twenty years and will continue to decline. The reduction of America's
contribution to global CO2 emissions would reduce potential warming by only a fraction of a
degree, and the result of any stabilization of CO2 emissions in all the developed countries would
be relatively insignificant in the context of reducing global greenhouse gas levels. The costs of
controlling CO2 emissions would be higher in the United States than in most other countries as a
result of the greater per capita energy use due to geographic and socio-economic patterns, (i.e.,
transportation of people and goods). Adopting more expensive CO2 controls will, therefore,
impose a disproportionate penalty on U.S. industry and will give foreign competitors a
competitive advantage over U.S. producers.
Policy Efforts to Control CO2 Emissions
Most industrialized nations, including the United States, already have policies and programs in
place that will help reduce emissions of CO2. In the United States, some studies show that
existing programs (such as EPA's Green Lights Program) and policies (such as the Clean Air Act
and the National Energy Policy Act of 1992) will come close to reducing CO2 emissions to 1990
levels by the year 2000.
Some economists believe that carbon dioxide emission reduction policies (i.e., carbon and other
energy taxes) will only provide an incentive for carbon intensive industries to migrate to regions
without such a tax. They say this movement to developing countries, where environmental
regulations are significantly less stringent than the U.S., will result in more greenhouse gas
emissions, not less.
As developed nations make progress toward reducing their emissions over the next decade, the
greatest opportunities (and needs) for controlling the growth in CO2 emissions will be in
developing countries and countries with economies in transition. International policy efforts will
need to be aimed at making the most of these opportunities by encouraging these nations to
incorporate clean technologies into their economies.
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