4/8/09

Overturning the Gulf Stream Myth (Word Climate Report)

October 3, 2006
Filed under:
Climate Changes, Gulf Stream

Do you recall seeing the classic film Day After Tomorrow? The theme of the movie was that humans warmed the earth, the global hydrological cycle was severely disrupted, fresh water began flowing into the North Atlantic, the Gulf Stream slowed rather suddenly, and Europe, and then the rest of the world, plunged into a glacial state. If you did not get the message in that film, Al Gore raised the possibility in his recent thriller.
But one is hard pressed to find evidence to support the idea that this is a real possibility. While there are some articles in the professional literature suggesting that the freshening of the waters of the North Atlantic has already begun, the conclusions in these articles are far from being universally accepted, and even farther from being the last word. There also exist articles showing no theoretical or empirical evidence to support the Gulf Stream story as it is pitched by Gore and followers.
In a recent article in American Scientist, Richard Seager of Columbia University’s Lamont-Doherty Earth Observatory wrote a piece regarding his long-time interest and work on the Gulf Stream and the climate of Europe. Richard grew up in England, and like the rest of us, learned early in life that England was relatively warm in winter for its latitude because of the Gulf Stream pumping large amount of heat from the Gulf of Mexico. He moved to New York during a heat wave that dwarfed anything he’d ever seen in Liverpool only to suffer through bitter cold only a few months later. No one denies that the climates of northern Europe are remarkably mild given their position on the Earth.
Richard Seager completed a Ph.D. at Columbia and assumed a postdoctoral position at the University of Washington in Seattle. He found the climate in Seattle remarkably similar to what he had experienced in Europe, but there is no Gulf Stream in the Pacific to account for the mild winters of coastal Washington and British Columbia. The Kuroshio Current in the Pacific Ocean moves due eastward and does not provide heat energy to the latitudes of Seattle. His experience in Seattle was not enough to make him question the notion that the Gulf Stream is responsible for the mild climate of Europe, but while in Seattle, he met atmospheric sciences professor David Battisti who he describes as “one of those great scientists who, with relish and an air of mischief, loves to question conventional wisdom.” Sometime six years ago, they discussed testing the Gulf Stream – European climate connection.
The two knew full well that the Gulf Stream carries a tremendous amount of heat out of the Gulf of Mexico and northward along the east coast of North America. Heat is lost to the atmosphere all along the way, but by the time the Gulf Stream is near the middle of the Atlantic the current has lost most of its heat, the water has become salty because of evaporation, and the cool, dense water sinks. The return flow occurs at the bottom of the North Atlantic and completes the “Atlantic conveyor.”
Seager and Battisti decided to conduct a series of numerical modeling simulations with two very different climate models. They ran the models in standard mode allowing for the heat moved by ocean currents to influence the climate of the planet. They then altered the computer code not allowing the ocean in the models to transport heat horizontally. Amazingly, they found that the ocean off the coast of northern Europe had approximately the same temperature with or without ocean heat transport. Seager wrote “This result would suggest that oceanic heat transport does not matter at all to the difference between the winter climates of western Europe and eastern North America!”
So was this the finding of the decade? No, it was not a new finding at all. Seager notes “Pretty much everything we had found could have been concluded on the basis of results that were already available.” Others had conducted similar numerical experiments, published the results in leading professional journals, and had basically debunked the Gulf Stream – Europe climate myth decades ago.
In finishing the essay, Seager blames modern-day climate scientists for continuing to promulgate the Gulf Stream – climate myth. He says “The abdication of responsibility leaves decades of folk wisdom unchallenged, still dominating the front pages, air waves and Internet, ensuring that a well-worn piece of climatological nonsense will be passed down to yet another generation.”
For another view along the lines of the same sentiments concerning Gulf Stream/climate change mischaracterization, see the following letter to the editor of the Economist.com by M.I.T. professor of physical oceanography Dr. Carl Wunsch, which includes the following:
One of the reasons the discussion of climate change is so frustrating is the continued dissemination of a basic error (A survey of climate change, September 9th). Your statement that “The Gulf Stream is driven both by the rotation of the Earth and by a deep-water current called the Thermohaline Circulation” is false. The Gulf Stream is a wind-driven phenomenon (as explained in a famous 1948 paper by Henry Stommel). It is part of a current system forced by the torque exerted on the ocean by the wind field. Heating and cooling affect its temperature and other properties, but not its basic existence or structure. As long as the sun heats the Earth and the Earth spins, so that we have winds, there will be a Gulf Stream (and a Kuroshio in the Pacific, an Agulhas in the Indian Ocean, etc).
Reference:
Seager, R. 2006. The Source of Europe’s Mild Climate. American Scientist, 94, 334-341.

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