Global warming can cause
Scientists announced in the July 21, 1999, edition of the journal Nature findings that suggest that global warming can sometimes lead to cold weather or even a worldwide freeze.
Scientists have long known that a severe cold spell occurred after the end of the Pleistocene glaciation, approximately 8,200 years ago. The cause, however, has been a mystery. The authors of the Nature article write that the centuries long cold spell might have been caused by meltwater from the disappearing glaciers, cooling the North Atlantic.
The Laurentide Ice Sheet covered parts of North America with ice up to two miles thick for more than a million years. When the Earth began to warm 10,000 years ago, it retreated back toward the poles. The ice sheet left in its wake at least two lakes containing more water than the Great Lakes combined.
In the Hudson Bay, ice held the water in place like a plug in a bathtub. When the plug finally melted, trillions of gallons gushed into the Labrador Sea, flowing out at 100 times the rate water leaves the Mississippi.
The conclusions of the authors are the result of a study by University of Colorado and Canadian researchers who examined evidence of this huge flood in the Hudson Bay region of Quebec and Ontario.
Independent research showed that global temperatures dropped significantly within several hundred years of the flood. Until this study, nobody could pinpoint if these two events were connected, said the study's lead author, University of Colorado geologist Don Barber. The scientists used radiocarbon dating of clams in the flood sediment, and other evidence, to correlate the two events.
The Atlantic Gulf Stream normally acts like a conveyor belt to deliver warm tropical water to temperate regions. By adding so much cold fresh water in such a short time, the flood shut down the Gulf Stream, said Richard Alley, a climate expert at Penn State University.
Temperatures in Greenland and Europe dropped by 6 to 15 degrees for at least 200 years, according to ice core data.
The authors conclusions demonstrate how global warming can, paradoxically, provoke a global freeze. If a modern glacier such as the Greenland Ice Sheet melts as a result of rising temperatures in the next century, it could trigger a similar flood and climate fluctuation, the researchers said.
Copyright © 1999 by Jeff Poling. Quotes are from media sources.
Revised: August 2, 1999; New: July 19, 1999