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Global warming refers to the increase 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 last 50 years is attributable to human activities". The increased volumes of carbon dioxide and other greenhouse gases 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 IPCC predict that global temperatures may increase by between 1.4 and 5.8 °C between 1990 and 2100. The range of uncertainty results in large part from not knowing the volume of future carbon dioxide emissions. In addition, there is 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. Such changes may increase the frequency and intensity of extreme weather events such as floods, droughts, heat waves, and hurricanes. This may also cause lower agricultural yields, glacier retreat, reduced summer streamflows, or contribute to biological extinctions.
Although warming is expected to affect the number and magnitude of these events, it is difficult to connect any particular event to global warming. Although most studies focus on the period up to 2100, warming (and sea level rise due to thermal expansion) would be expected to continue past then, since CO2 has a long average atmospheric lifetime. [1].
The term 'Global warming' is a specific case of the more general term 'climate change' (which can also refer to cooling, such as in Ice ages). Furthermore, the term is in principle neutral as to the causes, but in common usage, 'global warming' generally implies a human influence. Note, however, that the UNFCCC uses 'climate change' for human caused change and 'climate variability' for non-human caused change [2]. Some organizations use the term 'anthropogenic climate change' for human induced changes.
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