Friday, December 29, 2006

What Is Global Warming ?

This image will explains about Global Warming.

Global warming is the observed increase in the average temperature of the Earth's atmosphere and ocenas in recent decades. The Earth's average near-surface atmospheric temperature rose 0.6 ± 0.2 °celsius(1.1 ± 0.4 °fahrenheit) in the 20th century . The current scientific ocnsensus is that "most of the observed warming over the last 50 years is likely to have been attributable to human activities".
The main cause of the human-induced component of warming is the increase in atmospheric green house gases (GHGs), especially carbon dioxide (CO2), due to activities such as the burning of fossil fuels, land clearing, and agriculture.
Greenhouse gases are gases that contribute to the greenhouse effect. This effect was first described by Joseph Fourier in 1824, and was first investigated quantitatively in 1896 by the Swedish chemist Svante Arrhenius.
Climate sensitivity is a measure of the equilibrium response to increased GHGs, and other anthropogenic and natural climate forcings. It is found by observational and model studies. This sensitivity is usually expressed in terms of the temperature response expected from a doubling of CO2 in the atmosphere, which, according to the 2001 IPCC report, is estimated to be between 1.5 and 4.5 °C (2.7–8.1 °F) (with a statistical likelihood of 66-90%). This should not be confused with the expected temperature change by a given date, which also includes a dependence on the future GHG emissions and a delayed response due to thermal lag, principally from the oceans. Models referenced by the Intergovernmental Panel on Climate Change (IPCC), using a range of SRES scenarios, project that global temperatures will increase between 1.4 and 5.8 °C (2.5 to 10.5 °F) between 1990 and 2100.
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, glacial retreat, reduced summer stream flows, 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, warming (and sea level rise due to thermal expansion) is expected to continue past then, since CO2 has an estimated atmospheric lifetime of 50 to 200 years. Only a small minority of climate scientists disagree that humanity's actions have played a major role in recent warming. However, the uncertainty is more significant regarding how much climate change should be expected in the future, and there is a hotly contested political and public debate over implementation of policies that deal with predicted consequences, what, if anything, should be done to reduce or reverse future warming, and how to deal with the predicted consequences.

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