globalwarming is the observed increase in the average temperature of the Earth's atmosphere and oceans in recent decades and its projected continuation. Models referenced by the Intergovernmental Panel on Climate Change (IPCC) predict that global temperatures are likely to increase by 1.1 to 6.4 °C (2.0 to 11.5 °F) between 1990 and 2100.[1] The uncertainty in this range results from two factors: differing future greenhouse gas emission scenarios, and uncertainties regarding climate sensitivity.
Global average near-surface atmospheric temperature rose 0.74 ± 0.18 °Celsius
(1.3 ± 0.32 °Fahrenheit) in the last century. The prevailing scientific opinion
on climate change is that "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,"[1] which leads to
warming of the surface and lower atmosphere by increasing the greenhouse effect.
Greenhouse gases are released by activities such as the burning of fossil fuels,
land clearing, and agriculture. Other phenomena such as solar variation and
volcanoes have had smaller and probably negative effects 1950.[2] A small number
of scientists disagree with regard to the nature of the observed warming. Svante
Arrhenius first predicted CO2-induced global warming in 1896.
An increase in global temperatures can in turn cause other changes, including
a rising sea level and changes in the amount and pattern of precipitation. These
changes may increase the frequency and intensity of extreme weather events, such
as floods, droughts, heat waves, hurricanes, and tornados. Other consequences
include higher or lower agricultural yields, glacier retreat, reduced summer
streamflows, species extinctions and increases in the ranges of disease vectors.
Warming is expected to affect the number and magnitude of these events; however,
it is difficult to connect particular events to global warming. Although most
studies focus on the period up to 2100, even if no further greenhouse gases were
released after this date, warming (and sea level) would be expected to continue
to rise for more than a millennium, since CO2 has a long average atmospheric
lifetime.
Remaining scientific uncertainties include the exact degree of climate change
expected in the future, and especially how changes will vary from region to
region across the globe. A hotly contested political and public debate also has
yet to be resolved, regarding whether anything should be done, and what could be
cost-effectively done to reduce or reverse future warming, or to deal with the
expected consequences. Most national governments have signed and ratified the
Kyoto Protocol aimed at combating global warming.
source wikipedia
