Windswept_ The Story of Wind and Weather - Marq de Villiers [44]
The conveyor belt is formed by water from the Florida Current, which circulates through the Gulf of Mexico and the Straits of Florida, and the North Equatorial Current, which flows westward along the equator. The resultant Gulf Stream parallels the coast of North America along a boundary separating the warm and more saline waters of the Sargasso Sea to the east from the colder, slightly fresher continental slope waters to the north and west. It more or less bounces off Cape Cod and is bent eastward, in the general direction of Ireland.
The Gulf Stream then feeds into the North Atlantic Current, which splits in northern and southern directions along the west coast of Ireland. The southward flow turns into the Canary Current, named for the Canary Islands off the coast of southwestern Morocco in North Africa, and thence bends westward parallel to the equator, winding up once more off Florida. Water flowing north along the west coast of Britain becomes the Norwegian Current, as it moves along the coast of Norway.
At least on the surface. Deeper down, the patterns are more complex.
When Gulf Stream water enters northern latitudes, it cools and sinks, becoming saltier and denser in the process (the haline in thermohaline). This happens in curious, slowly revolving "pipes" that take water from the surface to the seabed, mostly in the Labrador Sea and the Greenland Sea. At this low level, the water moves south and circulates around Antarctica; thence north again to the Indian, Pacific, and finally the Atlantic basins. The Smithsonian Institution estimates that it can take a thousand years for water from the North Atlantic to find its way into the North Pacific.
It is pretty obvious that changes in this massive circulatory device would have profound impacts, not just on wind but on climate generally. It is one of the main worries about global warming that increasing Arctic ice melt might alter or, worse, stop, the Gulf Stream, at least for a period. This indeed seems to be happening: The known vertical "pipes" have been reduced in number in the last few years from about a dozen to two, in part because the water is too warm to sink. The computer models all show that global warming would have a perverse short-term cooling effect on some northern places; instead of warming, Maritime Canada and northern New England, Ireland and the British Isles would go into a temporary deep freeze. I've sometimes contemplated this notion of my little house turning into Iceland, but it doesn't do to dwell too much on the possibility, because there are other, more immediately worrying things to be concerned about. For instance, a good deal of evidence suggests that changes in the velocity and direction of the conveyor belt might be a prime cause of the peculiar fact that hurricanes seem to wax and wane on a more or less thirty-year cycle. Is it just coincidence that the conveyor belt slowed down in the 1960s, cooling the North Atlantic slightly, in a period of fewer annual hurricanes? Or that the conveyor belt seems to have picked up speed starting in the 1990s, the decade when hurricanes started to increase in frequency again? Bob Sheets, former director of the National Hurricane Center in Miami, has asserted that the meteorological evidence suggests that the coming quarter century will produce more, and more intense, storms, and that "the thousands of people who moved to their dream homes during the hurricane low . . . could be in for some unpleasant time."23 It's also possible that it might be the other way around: The frequency of hurricanes may, by contrast, affect the thermohaline circulatory system.
For us on the American northeast coast, therefore, this expected deep freeze would be a mixed blessing. More ice, but fewer hurricanes. If the