Global warming 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 Warming Awareness 2007
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 but non-negligible effects on global mean temperature since 1950.[2] A few scientists disagree about the primary causes of the observed warming. Global Warming Awareness 2007
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 awareness 2007. Although most studies focus on the period up to 2100, even if no further greenhouse gases were released after this date,global warming (and sea level) would be expected to continue to rise for more than a millennium, since CO2 has a long average atmospheric lifetime. Global Warming Awareness 2007
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 globalwarming. (See: List of Kyoto Protocol signatories.) Global Warming Awareness 2007
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 but non-negligible effects on global mean temperature since 1950.[2] A few scientists disagree about the primary causes of the observed warming. Global Warming Awareness 2007
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 awareness 2007. Although most studies focus on the period up to 2100, even if no further greenhouse gases were released after this date,global warming (and sea level) would be expected to continue to rise for more than a millennium, since CO2 has a long average atmospheric lifetime. Global Warming Awareness 2007
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 globalwarming. (See: List of Kyoto Protocol signatories.) Global Warming Awareness 2007
Terminology
The term globalwarming is a specific example of the broader term climate change, which can also refer to global cooling. In principle, globalwarming is neutral as to the period or causes, but in both common and scientific usage the term generally refers to recent warming and implies a human influence.[3] The UNFCCC uses the term "climate change" for human-caused change, and "climate variability" for other changes.[4] Some organizations use the term "anthropogenic climate change" for human-induced changes.Global Warming Awareness 2007
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; the urban heat island is not believed to be significant. 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 (0.22 and 0.4 °F) per decade since 1979, according to satellite temperature measurements. Over the one or two thousand years before 1850, 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 for Space Studies, 2005 was the warmest year since reliable, widespread instrumental measurements became available in the late 1800s, exceeding the previous record set in 1998 by a few hundredths of a degree. Estimates prepared by the World Meteorological Organization and the UK Climatic Research Unit concluded that 2005 was the second warmest year, behind 1998.[5][6]
The attribution of recent climate change is clearest for the most recent period of the last 50 years, for which the most detailed data are available.
Note that the anthropogenic emissions of other pollutants—notably sulphate aerosols—exert a cooling effect; this partially accounts for the plateau/cooling seen in the temperature record in the middle of the twentieth century,[7] though this may also be due to intervening natural cycles.Global Warming Awareness 2007
Based on estimates by NASA's Goddard Institute for Space Studies, 2005 was the warmest year since reliable, widespread instrumental measurements became available in the late 1800s, exceeding the previous record set in 1998 by a few hundredths of a degree. Estimates prepared by the World Meteorological Organization and the UK Climatic Research Unit concluded that 2005 was the second warmest year, behind 1998.[5][6]
The attribution of recent climate change is clearest for the most recent period of the last 50 years, for which the most detailed data are available.
Note that the anthropogenic emissions of other pollutants—notably sulphate aerosols—exert a cooling effect; this partially accounts for the plateau/cooling seen in the temperature record in the middle of the twentieth century,[7] though this may also be due to intervening natural cycles.Global Warming Awareness 2007
Aucun commentaire:
Enregistrer un commentaire