Paradoxically, one outcome of global warming could be a dramatic cooling of Britain and northern Europe.

Evidence: (CNN) - Wednesday, May 11, 2005
Scientists now seem to have some evidence that changes are occurring in the Gulf Stream. Without the influence of the Gulf Stream the weather in Britain could be more like that of Siberia, which shares the same latitude.

Cambridge University ocean physics professor Peter Wadhams points to changes in the waters 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 feet below to the seabed. As that water sinks, it interacts with the warm Gulf Stream current flowing from the south.

But Wadhams says the number of these 'chimneys' has dropped from about
a dozen to just two. That could cause a weakening of the Gulf Stream, which could mean less heat reaching northern Europe. The activity in the Greenland Sea is part of a global pattern of ocean movement, known as thermohaline circulation, or more commonly the global conveyor belt.

Wadhams presented his findings at a meeting of the European Geosciences Union in Vienna, Austria. He said the slowing of the Gulf Stream could contribute to other severe effects on the planet, such as the complete melting of the Arctic ice cap in the summer months. That could eliminate the habitat and lead to the extinction of Arctic wildlife, including the polar bear. Current predictions indicate that could happen as early as 2020 or as late as 2080.

Other oceanographers stress that Wadhams' findings are one piece of a very complex earthly puzzle. Terrence Joyce, senior scientist in the department of physical oceanography at Woods Hole Oceanographic Institution in Massachusetts, says it's important not to get alarmist, but instead to keep up a wide array of research.

For a dramatic climate change to take place, "A whole bunch of pieces have to fit together. Certainly this is one of them. Such a dramatic climate change would not take place in five days, but rather several years", said Joyce.

The global conveyor belt

The global conveyor belt thermohaline circulation is driven primarily by the formation and sinking of deep water in the Norwegian Sea. This circulation is thought to be responsible for the large flow of upper ocean water from the tropical Pacific to the Indian Ocean through the Indonesian Archipelogo. The two counteracting forcings operating in the North Atlantic control the conveyor belt circulation: (1) the thermal forcing (high-latitude cooling and the low-latitude heating) which drives a polar southward flow; and (2) haline forcing (net high-latitude freshwater gain and low-latitude evaporation) which moves in the opposite direction.

In today's Atlantic the thermal forcing dominates, hence, the flow of upper current from south to north. When the strength of the haline forcing increases due to excess precipitation, or ice melt the conveyor belt will weaken or even shut down. The variability in the strength of the conveyor belt will lead to climate change in Europe and it could also influence other areas of the global ocean.

The gulf stream

Much of the sinking in the ocean happens in the North Atlantic limb
of the Conveyor. Warm waters are carried north by the Gulf Stream, cooling as they travel. During winter the coldest, saltiest waters sink thousands of metres below the surface to form North Atlantic Deep Water (NADW). The heat released
to the atmosphere during NADW formation is largely responsible for the relatively warm temperatures enjoyed by western Europe.