Mild Winters Mostly Hot Air, Not Gulf Stream

No British warming. Scandinavia benefits far more from the warming (blue) due to heat delivered by ocean currents than does the rest of Western Europe.

The idea that the Gulf Stream warms Europe dates back at least to the 1850s. But now a team of climate researchers reports that, in fact, the Gulf Stream does little to moderate European winters; instead, winds blowing across the Western Hemisphere play a bigger role than thought.

Climatologists have long agreed that some combination of wind and ocean currents makes Europe's winters milder than those of eastern North American regions at the same latitudes. Winds blowing toward Europe from the west pick up heat from the waters of the North Atlantic. Within eastern North America, however, winds don't blow directly west, arriving instead more from the frigid north. Then there's the Gulf Stream--the tail end of a great "conveyor belt" of currents carrying warm waters from the Southern Hemisphere--which also adds heat to winds heading for Europe. Together, these influences make British winters 15°C warmer than Labrador's, but it wasn't clear how big a role each mechanism played.

Climate researcher Richard Seager of Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York, decided to separate winds' effects from those of currents. Along with David Battisti of the University of Washington, Seattle, and other colleagues, Seager began by studying meteorological observations from the past half-century to calculate how the world's winds distributed heat over the globe. Then the group confirmed a minor role for the Gulf Stream by running climate models with and without heat transported by ocean currents. Comparing the two models, they determined that the Gulf Stream was crucial to warming Scandinavia and keeping the far northern North Atlantic free of ice. But even without the Gulf Stream's toasty influence, the wintertime temperature contrast between Europe south of Scandinavia and eastern North America was still about 15°C, the team reports in the October Quarterly Journal of the Royal Meteorological Society.

"It's an excellent paper," says meteorologist Rowan Sutton of the University of Reading, U.K. "The importance of the Gulf Stream in European climate is often overstated." The analysis will no doubt stoke the debate over the relative roles of the Gulf Stream and other forces that affect climate, adds Sutton.

Related sites
Lamont-Doherty Earth Observatory at Columbia
Joint Institute for Study of the Atmosphere and the Ocean at the University of Washington

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