College of LAS « Illinois

Atmospheric Sciences

Global Warming Could Cool Europe

Shut down of "global conveyor belt" is a possibility.

Richard Burkhardt

Could global warming actually lead to cooler temperatures in Europe?

At first glance, this sounds like a contradiction. But it is possible, says Michael Schlesinger, professor of atmospheric sciences at the University of Illinois.

This seemingly strange consequence could occur if global warming causes a shutdown of what some call the "global conveyor belt"—the tremendous northward flow of warm surface water in the Atlantic Ocean. As warm surface water moves north and cools, it drops to greater depths and then returns south—like a conveyor belt.

Popularly known as the Gulf Stream, this flow of water is technically called the Atlantic Thermohaline Circulation, or ATHC. As the ATHC conveyor belt transports warm water north, it carries enormous amounts of heat, which has a significant warming effect on Europe. In fact, according to Schlesinger, each year the ATHC transports northward about 1 petawatt of heat, which is a million billion Watts, the amount of energy that could run 100 Earth civilizations.

The transport of warm water north gives Europe its relatively mild winters when compared to other locations at the same latitude. But that could change if the conveyor belt stalls or shuts down—something that scientists believe happened 13,000 years ago, Schlesinger says.

But could it happen again?

The 2004 movie, The Day After Tomorrow, depicted it happening, triggering a sudden Ice Age in New York—a scenario that Schlesinger describes as "off the wall."

But despite the extreme Hollywood take on this subject, he says it is entirely possible for rising global temperatures to slow or shut down the ATHC conveyor belt. This, in turn, could bring cooler temperatures to Europe—without the big-screen special effects.

As temperatures rise, rainfall increases in the middle latitudes of the Atlantic and sea ice and mountain glaciers melt, he explains. These changes would add freshwater to the Atlantic, and too much freshwater could slow or shut down the ATHC conveyor belt.

"If the thermohaline circulation shut down, the southern hemisphere would become warmer and the northern hemisphere would become colder," he says. "The heavily populated regions of eastern North America and western Europe would experience a significant shift in climate."

Over the past seven years, Schlesinger's team has run simulations that take into consideration climatic changes to both the ocean and the atmosphere. Their computer models project a 70-percent likelihood of the ATHC conveyor belt shutting down in the next 200 years if current climate policy does not change.

In addition, they looked at whether these odds would be better if the world changed its climate policy. Specifically, Schlesinger's team studied what would happen if an immediate tax of $10 to $100 per ton of carbon were imposed, which essentially amounts to an additional 5 to 50 cents per gallon of gasoline, thereafter increasing annually at the rate of inflation. The resulting decrease in carbon dioxide emissions would reduce future global warming and the risk of a conveyor belt shutdown; but there would still be an 8 to 25 percent chance of a shutdown in the next 200 years.

After a shutdown, the North Atlantic could cool, but the U. of I. climate model shows a "phenomenal winter warming in Alaska and over the West Antarctic ice sheet," raising other risks, Schlesinger says. If the West Antarctica ice sheet "de-glaciated," the 16-foot rise in sea level would flood coastal cities across the world.

This scenario would make New Orleans look like child's play, he says. "So that's really a place we don't want to go."

Fall/Winter 2006–07