The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) is the fourth in a series of reports on climate change.
Two of the three reports (Working groups I and II) have been been published so far.
The first report concludes that global warming is happening, and is very likely caused by human emissions of greenhouse gases.
Climate Change 2007 The Physical Science Basis, the report of Working Group I, "assesses the current scientific knowledge of the natural and human drivers of climate change, observed changes in climate, the ability of science to attribute changes to different causes, and projections for future climate change." The report was produced by about 600 authors from 40 countries, and reviewed by over 620 experts and governments.
Before being accepted, the summary was reviewed line-by-line by representatives from 113 governments during the 10th Session of Working Group I, which took place in Paris, France, between 29 January and 1 February 2007. The key conclusions were that: It is "unequivocal" that global warming is occurring; the probability that this is caused by natural climatic processes is less than 5%; and the probability that this is caused by human emissions of greenhouse gases is over 90%. As a result it is predicted that, during the 21st century the following will occur. Regarding surface air warming in the 21st century, the best estimate for a "low scenario" is 1.8 degrees Celsius with a likely range of 1.1 to 2.9 degrees Celsius (3.2 degrees Fahrenheit with a likely range of 2.0 to 5.2 degrees Fahrenheit).
The best estimate for a "high scenario" is 4.0 degrees Celsius with a likely range of 2.4 to 6.4 degrees Celsius (7.2 degrees Fahrenheit with a likely range of 4.3 to 11.5 degrees Fahrenheit). Based on a model that excludes ice sheet flow due to a lack of basis in published literature, it is estimated that sea level rise will be, in a low scenario, 18 to 38 cm (7 to 15 inches) and in a high scenario, 26 to 59 cm (10 to 23 inches). It is more than 90% certain that there will be frequent warm spells, heat waves and heavy rainfall.
It is more than 66% certain that there will be an increase in droughts, intensity of tropical cyclones (which include hurricanes and typhoons) and extreme high tides. Working Group II reports on impacts, adaptation and vulnerability to climate change. The Working Group III volume analyses mitigation options.
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