Global warming

From Wikipedia, the free encyclopedia


Global warming is the observed increase in the average temperature of the Earth's atmosphere and oceans in recent decades and its projected continuation into the future.

Global average near-surface atmospheric temperature rose 0.6 ± 0.2 °Celsius (1.1 ± 0.4 °Fahrenheit) in the 20th century. The prevailing scientific opinion on climate change is that "most of the warming observed over the last 50 years is attributable to human activities."[1] The main cause of the human-induced component of warming is the increased atmospheric concentration of greenhouse gases (GHGs) such as carbon dioxide (CO2), 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.

Models referenced by the Intergovernmental Panel on Climate Change (IPCC) predict that global temperatures may increase by 1.4 to 5.8 °C (2.5 to 10.5 °F) between 1990 and 2100. The uncertainty in this range results from both the difficulty of predicting the volume of future greenhouse gas emissions and uncertainty about climate sensitivity.

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, warming (and sea level rise) is expected to continue past then, 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 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 combatting global warming. (See List of Kyoto Protocol signatories.)

Contents

* 1 Terminology
* 2 History of warming
* 3 Causes
o 3.1 Greenhouse gases in the atmosphere
o 3.2 Other hypotheses
+ 3.2.1 The solar variation theory
* 4 Attributed and Expected effects
* 5 Mitigation
* 6 Climate models
* 7 Other related issues
o 7.1 Ocean acidification
o 7.2 Relationship to ozone depletion
o 7.3 Relationship to global dimming
o 7.4 Pre-human global warming
o 7.5 Pre-industrial global warming
* 8 Notes
* 9 References
* 10 See also
* 11 External links
o 11.1 Scientific
o 11.2 Polar ice-related links
o 11.3 Other

Terminology

The term "global warming" is a specific case of the more general term "climate change" (which can also refer to "global 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.[2] Some organizations use the term "anthropogenic climate change" for human-induced changes.

History of warming

Relative to the period 1860-1900, global temperatures on both land and sea have increased by 0.75 °C (1.4 °F), according to the instrumental temperature record. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C/decade against 0.13 °C/decade (Smith, 2005). Temperatures in the lower troposphere have increased between 0.12 and 0.22 °C per decade since 1979, according to satellite temperature measurements. Over the one or two thousand years before 1850, world temperature is believed to have been relatively stable, with possibly regional fluctuations such as the Medieval Warm Period or the Little Ice Age.

Based on estimates by NASA's Goddard Institute