Global warming and climate change
Global warming is the increase in average temperature of Earth's
near-surface air and oceans since the mid-20th century and its projected
continuation. Global surface temperature increased 0.74 - 0.18 C (1.33 -
0.32 F) between the start and the end of the 20th century.
The Intergovernmental Panel on Climate Change (IPCC) concludes that
most of the observed temperature increase since the middle of the 20th
century was very likely caused by increasing concentrations of
greenhouse gases resulting from human activity such as fossil fuel
burning and deforestation.
The IPCC also concludes that variations in natural phenomena such as
solar radiation and volcanic eruptions had a small cooling effect after
1950. These basic conclusions have been endorsed by more than 40
scientific societies and academies of science, including all of the
national academies of science of the major industrialized countries.
Climate model projections summarized in the latest IPCC report
indicate that the global surface temperature is likely to rise a further
1.1 to 6.4 C (2.0 to 11.5 F) during the 21st century. The uncertainty in
this estimate arises from the use of models with differing sensitivity
to greenhouse gas concentrations and the use of differing estimates of
future greenhouse gas emissions. Most studies focus on the period
leading up to the year 2100. However, warming is expected to continue
beyond 2100 even if emissions stop, because of the large heat capacity
of the oceans and the long lifetime of carbon dioxide in the atmosphere.
An increase in global temperature will cause sea levels to rise and
will change the amount and pattern of precipitation, probably including
expansion of subtropical deserts. Warming is expected to be strongest in
the Arctic and would be associated with continuing retreat of glaciers,
permafrost and sea ice. Other likely effects include changes in the
frequency and intensity of extreme weather events, species extinctions,
and changes in agricultural yields. Warming and related changes will
vary from region to region around the globe, though the nature of these
regional variations is uncertain.
Reuters |