Paris, 2 Feb 2007 -- The world's climate scientists today reported unequivocally that the Earth's climate system is increasingly heating up and that it likely has not been this warm for at least 1300 years. The fourth report of the UN's Intergovernmental Panel on Climate Change says that evidence for this includes more than increases in global average air and ocean temperatures.
As has been reported on this site, heating effects are strong in melting of snow and ice, rising global mean sea level, widespread changes in precipitation amounts, ocean salinity, wind patterns and aspects of extreme weather including droughts, heavy precipitation, heat waves and the intensity of tropical cyclones.
Coal Power With much stronger language and more assurance than in previous reports, the IPCC members said there was less than 10 percent chance that this global warming was natural -- they pinned it directly on human greenhouse gas emissions. The amount of CO2 spewed out per year from fossil fuel burning is 12 percent greater now than in the 1990s, their report indicated, and the amount of the greenhouse effect is the greatest in 10,000 years.
The forecast range of possible temperatures by the end of the century reaches higher in this report than did the previous one in 2001 --11.5 degrees F -- but the more probable range is between 3.2 and 7 degrees F. The rate of rise depends on if and how fast emissions are reduced and on possible adverse feed backs in the climate system.
All probable temperatures are far beyond the increase in the 20th C and will take modern civilization into uncharted territory. Temperatures are sure to rise faster in the next decades, the IPCC said, than they did during the same time span in the last half of the 20th century.
Sun Even now, the scientists reported, the last time the Arctic was significantly warmer was about 125,000 years ago, before the last ice age. At that time, sea level rose 4 to 6 meters as polar ice melted. For this coming century the IPCC is forecasting sea level to rise from 7 inches to about half a meter, depending on emissions and warming. The scientists expressed uncertainty about rapid melting of the Greenland ice cap, citing a lack of enough research so far; this is sure to be one of the more controversial parts of the report since some glaciologists think Greenland will add considerably more to sea level.
Scientists said "it is very likely that hot extremes, heat waves, and heavy precipitation events will continue to become more frequent," that it was very certain that the ocean would become more acid from taking up more CO2 and that the great currents in the North Atlantic were likely to slow but not stop.
Icicle DripIf CO2 emissions can be reduced far enough, the report estimated, the atmosphere could be stabilized at a much lower level of greenhouse effect than is forecast now. Still, the effects of global warming will be with us for many centuries, the IPCC said, because of the inertia of the atmosphere and oceans and the 100 + year persistence of greenhouse gases.
The significance of this report is less its absolute numbers, than in the strength of its judgments and its acceptance, in the UN's consensus procedure, by the world's nations including the U.S. and China. The IPCC will report in more detail later this year on changes to the natural world, and on mitigation and adaptation strategies to reduce the impact of climate change. Read the IPCC report.