The Great Ocean Conveyor Belt
by Daniel Grossman

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Poking the Angry Beast

Ruth Curry, a research scientist in the Woods Hole Oceanographic Institute, studies signs of global warming. - photo by Daniel Grossman

There's some evidence that extra rain has already begun. Rainfall in mid- and high-northern latitudes increased by about 10 percent in the 20th century. Ruth Curry, a scientist at the Woods Hole Oceanographic Institute in Falmouth, Massachusetts, says she has evidence that this and other recent climate changes are having an impact. Curry is sitting on a dock next to the research vessel Oceanus as workers ready it for sea.

"The upper ocean salinities in the tropics and subtropics of the Atlantic have been getting saltier," says Curry, "And the waters at the higher latitudes have been getting fresher."

In the scientific journal Nature, Curry wrote that these changes have been going on for 40 years and began to speed up in the 1990s. They're exactly the sort of changes Broecker fears could cause the conveyor, also called the Thermohaline Circulation, to shut off. Curry says there hasn't been any notable impact on the conveyor so far. But it is worrisome.

"Preconditioning is taking place. All of the steps that are required to alter the Thermohaline Circulation are in fact taking place," says Curry.

Some scientists say global warming's extra precipitation is enough to complete the triggering process. Ruth Curry thinks it might take something more dramatic, like a big piece of Greenland's ice sheet breaking off - a process some experts say might happen within the next century.

Above professor Wally Broecker's desk is a large plush stuffed snake with a sign on it that says "Angry Beast." It refers to the researcher's view that climate sometimes responds ferociously to the slightest provocation.

Broecker says, "By adding CO2 to the atmosphere we're poking it."

And if poking the angry beast causes the great conveyor to shut down, Europe would almost certainly get cooler again. Wally Broecker says the most serious consequence could be long deep droughts, like the one that destroyed the Akkadian Empire. He says he doesn't expect the beast to get angry in less than several decades. By then global warming will probably have made the north Atlantic too warm to freeze over as it did in the past. So the impact won't be the same as in previous incidents.

Still, as Broecker points out, "You don't want the conveyor to stop and then find out what its effects are. That's probably the only way we'll really find out is to do it. And if you do, it's sort of irreversible. You're not going to make it turn on artificially. It'll turn on when it's ready. That might be fifty years; it might be a couple hundred years."

Next - Urgent Problem or Not?

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