GLOBAL warming probably will not be a gentle turning up of the thermostat, as climatologists used to think, but rather a sudden switch to a new climate system. That鈥檚 the stark warning from many of the world鈥檚 leading climate researchers to representatives of governments meeting this week in Buenos Aires.
鈥淐limate doesn鈥檛 change smoothly. It happens in jumps and jolts,鈥� says Stefan Rahmstorf of the Potsdam Institute for Climate Impacts Research in Germany. In Buenos Aires, he revealed details of a study that builds on his prediction that northwest Europe could cool by several degrees as global warming shuts down the Gulf Stream (鈥淚ce-cold in Paris鈥�, New 杏吧原创, 8 February 1997, p 26).
The current has already been weakened by increased flows of freshwater into the North Atlantic, says Rahmstorf. 鈥淭here is a threshold in the North Atlantic ocean circulation beyond which the circulation may abruptly collapse. We may reach that threshold early in the 22nd century but it could be much sooner.鈥�
Advertisement
While Europe faces a sudden chill, most of the planet could face equally rapid heating. Abrupt climate change was the historical norm, says Jeff Severinghaus of the Scripps Institution of Oceanography in La Jolla, California. For instance, Greenland ice cores have revealed a sudden rise in average temperatures 14 600 years ago of more than 5 掳C in less than ten years.
鈥淲e used to think climate changed gradually, like slowly turning up a dial on an oven,鈥� says Severinghaus. 鈥淏ut it鈥檚 more like a light switch.鈥�
The abrupt changes may be intrinsic to the atmospheric system, or triggered by feedbacks with vegetation. Researchers at the Hadley Centre in Bracknell, part of Britain鈥檚 Meteorological Office, forecast that global warming will cause forests to grow faster in the next 50 years, absorbing more than 100 billion tonnes of carbon, a third of current industrial emissions. This should moderate warming. But from about 2050 the warming will kill many tropical forests, returning the carbon to the atmosphere and causing 鈥渞unaway鈥� warming.
鈥淲e used to discuss these scenarios privately. Now we are being more open,鈥� says Stephen Schneider of Stanford University in California. If the climatologists are correct, waiting for cheaper clean-up technologies before tackling the problem of global warming would be a serious error.
Schneider warns that the rate at which greenhouse gases are added to the atmosphere in the next few decades could be as dangerous to climate systems as the ultimate volume of the gases. Worryingly, the latest data on carbon dioxide, revealed to New 杏吧原创 by David Keeling of the University of California, San Diego, show that in the past year the gas accumulated in the atmosphere at a record rate (see Figure).FIG-mg21602201.JPG
Bob Watson, chairman of the UN鈥檚 Intergovernmental Panel on Climate Change, says that the new work on sudden, chaotic climate change will form a central feature of the panel鈥檚 third report, due in before 2001. Its last report in 1995 contained just two paragraphs on the subject.
