The origin of the Gulf Stream is debatable. One group of scientists believes that the Gulf Stream is driven both by the rotation of the Earth and by a deep-water current called the thermohaline circulation. Another group of scientists accept the theory propounded by Henry Stomme in 1948, that the Gulf Stream is a wind-driven phenomenon. Heating and cooling affect its temperature and other properties, but not its basic existence or structure. Stomme theorized that as long
as the sun heats the Earth and the Earth spins, there will be winds, and there will be a Gulf Stream.
There is some speculation that global warming could decrease or shut down thermohaline circulation, and therefore reduce the North Atlantic Drift. The time frame for this might happen is unclear; estimates range from few decades to a few hundred years. This could trigger localized cooling in the north Atlantic and lead to cooling (or lesser warming) in that region, particularly affecting areas such as the Scandinavian countries and the United Kingdom. The slowdown, which climate modelers have predicted will follow global warming, has been confirmed by the most detailed study yet of ocean flow in the Atlantic. Most alarmingly, the new research reveals that a part of the current, which is usually 60 times more powerful than the Amazon River of South America, came to a temporary halt during November 2004.
Recent research has shown that changes are occurring in the Gulf Stream. According to scientists, in the absence of the Gulf Stream and its two northern branches, the north Atlantic Drift and the Canary Current, the weather in the United Kingdom could be more like that of Siberia, which lies on the same latitude. According to Peter Wadhams of the University of Cambridge, changes are occurring in the water of the Greenland Sea. Historically, large columns of very cold, dense water in the Greenland Sea, known as chimneys, sink from the surface of the ocean to about 9,000 ft. (2,743 m.) below, to the seabed. As that water sinks, it interacts with the warm Gulf Stream current flowing from the south. However, the number of those chimneys, according to Wadhams, has decreased from about a dozen to just two. That is causing a weakening of the Gulf Stream, Wadham asserts, which could mean less heat reaching northern Europe. It is possible that the coastal areas of western Europe could be converted into deserts. However, this would require much more extensive research on changing land use patterns in coastal areas.
Harry Bryden, of the National Oceanography Centre in Southampton, presented his findings to a conference in Birmingham on rapid climate change. Bryden's research group stunned climate researchers in 2006, with data suggesting that the flow rate of the Atlantic circulation had dropped by about 6 million tons of water a second 1957-98. If the current remained that weak, Bryden predicted, it would lead to a one degree C drop in the United Kingdom in the next decade. A complete shutdown would lead to a 7-11 degree F (4-6 degree C) cooling over 20 years.
Bryden's study prompted the United Kingdom's National Environment Research Council to set up an array of 16 submerged stations spread across the Atlantic, from Florida to northern Africa, to measure the flow rate and other variables at different depths. Data from these stations confirmed the slowdown in 1998 was not a "freak observation," although the current does seem to have picked up slightly since then. Richard Seager, who presented his research to the New York Academy of Sciences on "The Gulf Stream: European Climate and Abrupt Climate Change," expressed similar views. Seager states that a slowdown of the Gulf Stream and ocean circulation in the future, induced by freshening of the waters caused by anthropogenic climate change (via melting of glaciers and increased water vapor transport into high latitudes) or simply by warming, would introduce a modest cooling tendency. This would leave the temperature contrast across the Atlantic unchanged. In fact, the cooling tendency would probably be overwhelmed by the direct radia-tively driven warming from rising greenhouse gases.
SEE ALSo: Current; North Atlantic Oscillation; Ocean Component of Models; Oceanic Changes; Thermohaline Circulation.
BIBLIoGRAPHY. J. Randerson, "Sea Change: Why Global Warming Could Leave Britain Feeling the Cold," Guardian (October 27, 2006); R. Seager, "Climate Mythology: The Gulf Stream, European Climate and Abrupt Change," lecture delivered to the New York Academy of Sciences (June 7, 2007); M. Walton, "Changes in Gulf Stream Could Chill Europe," CNN (May 10, 2005); Carl Wunsch, "Climate Change and the Gulf Stream," Economist (October 5, 2006).
JAWAHARLAL NEHRU UNIVERSITY
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