|
|
|
|
Global Warming This Century Called Unprecedented A scientist at the National Oceanic and Atmospheric Administration said on Dec 7, 1998, that global warming in this centruy is greater than at any time in the last 1,200 years, and human activity is partly to blame. By Joby Warrick, Washington Post Start Date: 12/8/98 The warming of the Earth in this century is without precedent in at least 1,200 years and cannot be fully explained by any known combination of natural forces, one of the federal government's top climate scientists said yesterday. New research that documents climate change as far back as the Holy Roman Empire is strengthening the argument that humans are partly responsible for the rising temperatures, said Jonathan Overpeck, head of the paleoclimatology program for the National Oceanic and Atmospheric Administration. "There is no period that we can recognize in the last 1,200 years that was as warm on a global basis," said Overpeck, who presented his findings at a meeting of the American Geophysical Union in San Francisco. "That makes what we're now seeing more unusual, and more difficult to explain without turning to a 'greenhouse gas' mechanism." Overpeck made the assertion as the eastern half of the United States basked in an extended December heat wave that has shattered temperature records in dozens of cities. Although the warm itself, evidence of global warming, a sharp spike in global temperatures in the past two years has intensified the debate over humankind's contribution to climate change. New scientific findings presented in San Franciso appeared to simultaneously add clarity and confusion to the debate. While some researchers reported strong signals of human-induced warming in the past century, other scientists acknowledged enormous uncertainties that complicate the task of forecasting climate change in the future. One of the speakers, James E. Hansen, director of NASA's Goddard Institute for Space Studies, argues that scientists know too little about the complexities of climate, such as changes in cloud cover, to make accurate predictions. Hansen, who told a congressional panel in 1988 that the greenhouse effect "is here," caused a stir a month ago when he wrote about those uncertainties in a prominent journal, The Proceedings of the National Academy of Sciences. "The forcings that drive long-term climate change are not known with an accuracy sufficient to define future climate change," Hansen wrote. Overpeck, in his speech, said this century's warmer temperatures are appearing more anomalous as scientists improve their understanding of climate change in the past. Not only has the 20th century produced the hottest years on record, he said, but the magnitude of change appears to be without parallel since at least 800 A.D. Until very recently, many scientists believed the Earth underwent a dramatic warming in the Middle Ages, beginning around the 9th century and continuing until nearly the 14th century. During the "Medieval Warm Period," as it is called, temperatures rose throughout Europe and sea ice retreated in the North Atlantic, allowing the Vikings to briefly colonize Greenland. Global warming skeptics frequently cite the era as one of the best known, historic examples of natural climate variation -- proof, they say, that climate changes without help from people, and that a little warming might even be beneficial. But new research suggests the Medieval Warm Period never really happened, Overpeck said. Based on evidence from ancient tree rings,glaciers and other "proxy" measurements of past climate, the thaw appears to have been limited to northern latitudes in Europe and North America, while other parts of the globe saw little change in temperature. The apparent cause of Europe's warming was a change in ocean currents, he said. "Our study of the Medieval Warm Period supports the likelihood that no known natural phenomenon can explain the record 20th century warmth," Overpeck said. "Twentieth century global warming is a reality and should be taken seriously." The average temperature at the Earth's surface has risen about 1 degree Fahrenheit since the 1880s, with many of the century's warmest years occurring in the past decade. Scientists predict 1998 will surpass 1997 as the warmest year since record-keeping began. [Disclaimer: This article is copyright (c) The Washington Post Company. The information contained in this story may not be republished, broadcast, rewritten or otherwise distributed without prior written permission of The Washington Post. This text is posted in the public interest.]
Built by Frontier on a Macintosh on 6/17/00; 11:52:10 AM. Web Comments  -
Produced by Larry LoweServed 1492 times since 12/8/98. |
|
