Gulf Stream

Ocean currents affect not only the temperature, but also the precipitation on land areas adjacent to the ocean. A cold ocean current near land causes the air just above the water to be cold, while the air above is warm. There is very little opportunity for convection, thus denying moisture to nearby land. Coastal deserts of the world usually border cold ocean currents. Contrary to this, warm ocean currents, such as Gulf Stream, bring moisture to the adjacent land areas. The Gulf Stream, together with its northern extension toward Europe, the North Atlantic Drift, is a powerful, warm, and swift Atlantic Ocean current that originates in the Gulf of Mexico, exits through the strait of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean. It carries a huge amount of warm water to northerly lands, which has enormous significance to inhabitants of those areas; without it, northern Europe would be much colder and drier.

At about 30 degrees W, 40 degrees N, it splits into two, with the northern stream crossing northern Europe, and the southern stream (Canary Current) recirculating off western Africa. The Gulf Stream influences the climate of the east coast of North America from Florida to Newfoundland, and the west coast of Europe. Warm water brought to Europe’s shores raises the temperature by as much as 18 degrees F (10 degrees C) in some places.

Gulf Stream Origins

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 accepts 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 in which this might happen is unclear; estimates range from a 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, proving 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 from 1957 to 1998. If the current remained that weak, Bryden predicted, it would lead to a 1 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 that 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 radiatively driven warming from rising greenhouse gases.