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Abrupt Climate Change
Tue Aug 16, 2005
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 The Children’s Blizzard. The Weather Notebook is supported by Subaru of America. Or Climate Change Series is also funded by Environmental Defense.
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