9 May 2005

The world is now warmer than it has been at any point in the last two millennia

An excellent feature New Yorker article series on climate change by Elizabeth Colbert. All need to read this.
There is a very broad consensus in the scientific community that global warming is under way. To the extent that there are conflicting views, they are usually over how exactly the process will play out. This is understandable. The climate affects just about every natural system on earth, and these systems in turn affect the climate. So making predictions is very complicated. Meanwhile, we have only one planet, so it’s impossible to run a controlled experiment. To focus on the degree of disagreement, rather than on the degree of consensus, is, I think, fundamentally misguided. If ten people told you your house was on fire, you would call the fire department. You wouldn’t really care whether some of them thought that the place would be incinerated in an hour and some of them thought it would take a whole day.


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Global warming can cause global cooling
Jeff Poling

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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.