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Global Warming
Global warming is the increase in the average temperature of the Earth's
near-surface air and oceans in recent decades and its projected continuation.
The global average air temperature near the Earth's surface rose 0.74 ± 0.18
°C (1.33 ± 0.32 °F) during the last 100 years. The Intergovernmental Panel on
Climate Change (IPCC) concludes, "most of the observed increase in globally
averaged temperatures since the mid-20th century is very likely due to the
observed increase in anthropogenic greenhouse gas concentrations" via the
greenhouse effect. Natural phenomena such as solar variation combined with
volcanoes probably had a small warming effect from pre-industrial times to
1950 and a small cooling effect from 1950 onward. These basic conclusions have
been endorsed by at least 30 scientific societies and academies of science,
including all of the national academies of science of the major industrialized
countries. While individual scientists have voiced disagreement with some of
the main conclusions of the IPCC, the overwhelming majority of scientists
working on climate change are in agreement with them.
Climate model projections summarized by the IPCC indicate that average global
surface temperature will likely rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F)
during the 21st century. The range of values results from the use of differing
scenarios of future greenhouse gas emissions as well as models with differing
climate sensitivity. Although most studies focus on the period up to 2100,
warming and sea level rise are expected to continue for more than a millennium
even if greenhouse gas levels are stabilized. The delay in reaching
equilibrium is a result of the large heat capacity of the oceans.
Increasing global temperatures will cause sea level to rise, and is expected
to increase the intensity of extreme weather events and to change the amount
and pattern of precipitation. Other effects of global warming include changes
in agricultural yields, trade routes, glacier retreat, species extinctions and
increases in the ranges of disease vectors.
Remaining scientific uncertainties include the amount of warming expected in
the future, and how warming and related changes will vary from region to
region around the globe. There is ongoing political and public debate
worldwide regarding what, if any, action should be taken to reduce or reverse
future warming or to adapt to its expected consequences. Most national
governments have signed and ratified the Kyoto Protocol, aimed at reducing
greenhouse gas emissions.
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