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of greenhouse gases. As such, should greenhouse warming require
active intervention, the United States has a responsibility to do
its part to reduce greenhouse emissions, and unilateral action
could contribute significantly to a reduction in the rate of
emission growth. However, the U.S. role in greenhouse warming,
although large (approximately 20 percent of worldwide CO2-equivalent emissions), is not so large
that unilateral action could stabilize global climate. At least a
60 percent reduction in current worldwide CO2-equivalent emissions would be needed for
stabilization, according to the Intergovernmental Panel on Climate
Change (Intergovernmental Panel on Climate Change, 1991). As
discussed in Chapter 28, geoengineering options may be able to
reduce the amount of reduction required, but international
agreement and participation in such actions would be necessary in
order to undertake such action on a planetary scale.
Second, U.S. policy and technology will affect the inclination
and capability of other nations to respond to greenhouse warming.
The U.S. policy is of instrumental importance, both in meeting our
potential national responsibilities within the world community and
in leading constructive change in that community. The large
magnitude and long time scale of potential adjustments imply that
any response will require a coherent and sustained commitment on a
global scale. What is needed is not a single national policy, but a
long-term strategic perspective on greenhouse warming and its
implications for the world economy.
Third, developing countries are unlikely to be able to respond
to the potential threat of greenhouse warming at the same level as
industrialized countries. The United States should not focus
exclusively on interventions within its own boundaries because
greenhouse warming is a global issue and emission reduction in one
country could be as beneficial as in another. It may be appropriate
for the United States and other industrial economies to seek
low-cost opportunities for reducing greenhouse gas emissions in
developing countries, or to provide economic and technological
support, through the political process, should these countries
decide that such actions are warranted.
Three basic premises are central to the panel's comparison of
different mitigation policy options.
• First, possible responses to greenhouse warming should
be regarded as investments in the future of the nation and the
planet. That is, the actions needed would have to be
implemented over a long time. They should be evaluated as
investments, in comparison with other claims on the nation's
resources, bearing in mind their often widespread implications for
• Second, cost-effectiveness is an essential
guideline. The changes in energy, industrial practice, land
use, agriculture, and forestry that might be implemented to limit
greenhouse gas emissions, or the use of geoengineering options,
imply an investment effort lasting several generations and large
enough to affect the macroeconomic profile of the country. Costs of
climate policy therefore need to be considered as a central
element. A sensible guideline is cost-effectiveness: obtaining the
largest reductions in greenhouse gas emissions at the lowest cost
to society. Positive or negative effects of any mitigation option
on societal factors not related to greenhouse warming must also be
taken into account.