User:Mytwocents/Globalnull Warmingnull
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Global warming refers to the increases in the average temperature of the Earth's atmosphere and oceans that has been observed in recent decades. The scientific opinion on climate change is that the average global temperature has risen 0.6 ± 0.2 °C over the 20th century, and that it is likely that "most of the warming observed over the past 50 years is attributable to human activities". The increased volumes of carbon dioxide and other greenhouse gases (GHGs) released by the burning of fossil fuels, land clearing and agriculture, and other human activities, are the primary sources of the human-induced component of warming.
Observational sensitivity studies and climate models referenced by the Intergovernmental Panel on Climate Change (IPCC) predict that global temperatures may increase by between 1.4 and 5.8 °C between 1990 and 2100. The range of uncertainty is primarily the results of the difficulty of predicting the volume of future carbon dioxide emissions, but there is also some uncertainty about the climate sensitivity.
The increase in global temperatures is expected to result in other changes, including rises in 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, and hurricanes. It may cause lower agricultural yields, glacier retreat, reduced summer streamflows, and contribute to biological extinctions. Although warming is expected to affect the number and magnitude of these events, 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 a long average atmospheric lifetime. .
There are only a few scientists who contest the view that humanity's actions have played a significant role in increasing recent temperatures. However, more significant uncertainties exist regarding how much climate change should be expected in the future, and there is a hotly contested political and public debate over what, if anything, should be done to reduce or reverse future warming, and how to cope with the consequences.
The term 'global warming' is a specific case of the more general term 'climate change' (which can also refer to cooling, such as occurs during Ice ages). In principle, 'global warming' is neutral as to the causes, but in common usage, 'global warming' generally implies a human influence. However, the UNFCCC uses 'climate change' for human-caused change, and 'climate variability' for other changes . Some organizations use the term 'anthropogenic climate change' for human-induced changes.