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Abrupt Climate Change
Tue Jun 24, 2003
Listen in RealAudio 
Imagine Montreal's climate morphing into Miami's in the course of a single human lifetime -
from pond hockey to palm trees in 70 years. Sounds like science fiction, right?
Unfortunately, not. Hi, I'm Bryan Yeaton, and this is The Weather Notebook's weekly segment
on global climate change.
Recent studies of ice core samples have turned up striking evidence that this kind of rapid
and radical climate shift has occurred repeatedly in the past - and now there are unmistakable
signs that global warming may be plunging us into abrupt climate change once again.
We tend to think of climate as something that changes incrementally, a subtle tweaking of the
dial that takes centuries to register. But as one atmospheric scientist puts it, climate has
"switches as well as dials," and when one of those switches is flipped, changes occur
explosively. Around 12,700 years ago, temperatures in the North Atlantic plunged 5 degrees
Centigrade in the span of a single decade, and didn't budge for 1300 years. Climate again
shifted drastically about 8,200 years ago, triggering not only prolonged cold, but
catastrophic drought in the American West and other regions.
In both of these episodes, the abrupt climate change resulted from a sharp increase in the
amount of fresh water flowing into the North Atlantic, which effectively shut down a massive
heat distribution cycle known as the Ocean Conveyor. What's really alarming now is that fresh
water levels in the North Atlantic have been increasing at unprecedented rates, largely due to
global warming. Are we heading for abrupt climate change again? According to Dr. James
White, paleoclimatologist at the University of Colorado, Boulder: it's "probably
inevitable."
Today's story was contributed by David Laskin, author of Braving the Elements. The Weather
Notebook is supported by grants from The National Science Foundation, and Subaru, Driven by
What's Inside.
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