Thermohaline Circulation Debating Points

The idea that failure of the thermohaline circulation could cause colder temperatures on continents bordering the North Atlantic Ocean (North America and Europe) is highly debatable, as well as politically controversial. The debate was given extra force in 2001 when one of the idea's major proponents backed away from it. Earlier, Wallace S. Broecker of Columbia University had stated that "business as usual" fossil fuel use could trigger an abrupt reorganization of the Earth's thermohaline circulation. He also has said that doubling atmospheric levels of carbon dioxide could "cripple the ocean's conveyor circulation" (Broecker, 2001, 83).

Broecker (1987,123-126; 1997,1582-1588) suggested that if the Gulf Stream is blocked, winter temperatures in the British Isles could fall by an average of 11 °C, plunging Liverpool or London to the same temperatures as Spitsbergen, inside the Arctic Circle. Any dramatic drop in temperature could have devastating implications for agriculture and for Europe's ability to feed itself. In a book published by the American Association of Petroleum Geologists, however, Broecker nearly reversed his earlier position. Broecker said, "I apologize for my previous sins," of over-emphasizing the Gulf Stream's role (Kerr, 2002, 2202).

As is often the case in debates regarding global warming's possible effects on the Earth's ecosystem, the entire idea that a breakdown in the Gulf Stream could plunge Europe into a cold climate as the rest of the world experiences rising temperatures has been disputed. Is the Gulf Stream really the main climate driver warming Europe's winters? In October 2002, a team of scientists writing in the Quarterly Journal of the Royal Meteorological Society asserted that this popular assumption was incorrect. Rather, they maintained, Europe is warmed "by atmospheric circulation tweaked by the Rocky Mountains [and] ... summer's warmth lingering in the North Atlantic" (Kerr, 2002, 2202).

Richard Seager of Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York, and David Battisti of the University of Washington headed this study, which sought to determine the relative influences of various influences on European climate. They noted that winds carry five times as more heat out of the tropics to the midlatitudes than oceanic currents. They also estimated that roughly "80 percent of the heat that cross-Atlantic winds picked up was summer heat briefly stored in the ocean rather than heat carried by the Gulf Stream" (Kerr, 2002, 2202). Seager and colleagues relegate the Gulf Stream to the role of a minor player in Europe's wintertime climate. They asserted, however, that the Gulf Stream does play a major role in warming Scandinavia and keeping the far northern Atlantic free of ice (Seager et al., 2002, 2563).

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