Key Findings of the IPCC Second Assessment
During 1995, the Intergovernmental Panel on Climate Change
prepared its Second Assessment Report. U.S. scientists and research
findings played a pivotal role in the development of this assessment.
The following conclusions about climate change, its consequences,
and the potential for adaptation and mitigation are extracted from
the report. The IPCC findings provide important guidance for decision
makers and identify critical research questions that need to be
Effects of Human Activities on Regional and Global Climate, and on
- Human activities are increasing the atmospheric concentrations of
CO2 and other greenhouse gases that tend to warm the
and, in some regions, of aerosols that tend to cool the atmosphere.
- The Earth's climate is changing. The surface temperature this century
is as warm or warmer than any other century since at least 1400 AD;
the global average surface temperature has increased by 0.3° to
(about 0.5° to 1°F) over the last century; the last few decades have
been the warmest this century; sea level has risen 10 to 25 cm
(about 4 to 10 inches); and mountain glaciers have generally
retreated this century.
- Models that account for the observed increases in the atmospheric
concentrations of greenhouse gases and sulfate aerosols are
simulating the recent history of observed changes in surface
temperature and its vertical distribution with increasing realism.
- The balance of evidence suggests that there is a discernible human
influence on global climate.
- Without specific policies that reduce the growth of greenhouse gas
emissions, the Earth's average surface temperature is projected to
increase by about 1° to 3.5°C (about 2° to 6.5°F) by
2100-a rate of
warming that would probably be greater than any seen in the last
- The reliability of regional-scale predictions is still low, and the
degree to which climate variability may change is uncertain.
- Sea level is projected to rise by 15 to 95 cm (6 to 38 inches) by 2100.
- The long atmospheric lifetime of many greenhouse gases, coupled
with the thermal inertia of the oceans, means that the warming
effect of anthropogenic emissions will be long-lived.
- Even after a hypothetical stabilization of greenhouse gas
concentrations, temperatures would continue to increase for several
decades, and sea level would continue to rise for centuries.
Potential Health and Environmental Consequences of Climate
- Human-induced regional and global changes in temperature,
precipitation, soil moisture, and sea level add important new stresses
on ecological and socioeconomic systems that are already affected by
pollution, increasing resource extraction, and non-sustainable
- Most systems are sensitive to both the magnitude and rate of climate
- Many regions are likely to experience adverse effects as a result of
climate change, some of which are potentially irreversible; however,
effects of climate change in some regions may be beneficial.
- The projected changes in climate include potentially disruptive
effects that will affect the economy and the quality of life for this
and future generations:
- Human Health. will be adversely affected through an increase in
rate of heat-related mortality and in the potential for the spread of
vector-borne diseases such as malaria, dengue, yellow fever, and
encephalitis and non-vector-borne diseases such as cholera and
- Food Security. will be threatened in some regions of the world,
especially in the tropics and subtropics where many of the world's
poorest people live. On the whole, the effects of climate change over
the next century on total global food production may be small to
moderate in comparison to the effects of population change and
demands for improved nutrition.
- Water Resources. will be increasingly stressed, leading to
economic, social, and environmental costs, especially in regions that
are already water-limited and where there is strong competition
- Human Habitat Loss. will occur in regions where small islands
coastal plain and river areas are particularly vulnerable to sea level
- Natural Ecosystems. will be degraded because the composition,
geographic distribution, and productivity of many ecosystems will
shift as individual species respond to changes in climate. This may
lead to reductions in biological diversity and in the goods and
services ecosystems can provide for society.
- Developing countries are more vulnerable than developed countries
to climate change because of their socioeconomic conditions.
- Impacts will be hard to quantify with certainty because of
uncertainties in regional climate projections, the complicating effects
of multiple stresses, and a lack of understanding of some key
Approaches to Mitigate or Adapt to Climate Change
- Adaptation-which involves adjustments in practices, processes, or
structures of systems-can be helpful in reducing adverse impacts or
in preparing to take advantage of potential beneficial changes in
- Successful adaptation will depend upon education, technological
advances, institutional arrangements, availability of financing,
technology transfer, information exchange, and incorporation of
climate change concerns into resource-use and development
decisions. Potential adaptation options for many developing countries
are extremely limited due to the limited availability of technological,
economic, and societal capabilities.
- Options such as migration corridors to assist adaptation of natural
ecosystems to new climate conditions are, however, currently limited
and their effectiveness is generally unproven.
- Stabilization of the atmospheric concentrations of CO2 at
the pre-industrial concentration or less will eventually require
human-induced emissions of greenhouse gases to be cut below
- Gains in energy efficiency of 10-30% above present levels are
feasible at little or no cost in many parts of the world through
technical conservation measures and improved management
practices over the next 2 to 3 decades.
- Significant reductions in net greenhouse gas emissions can be
achieved utilizing an extensive array of technologies, and policy
measures that accelerate technology development, diffusion, and
transfer in all sectors.
- Flexible, cost-effective policies relying on economic incentives and
instruments, as well as internationally coordinated instruments, can
considerably reduce mitigation and adaptation costs.