Influence of the Gulf Stream on North Atlantic Climate

Climatology

Speculation about possible influence of the Gulf Stream on the climate of Europe arose in the early part of the 19th century. The winter of 1845-46 was unusually mild with heavy rains and high southwesterly gales, similar to the winter of 1821-22 when a Colonel Sabine had noted an unusual extension of the warm water of the Gulf Stream toward the shores of Europe. Struck by the similarity of weather, Sabine hypothesized that there might be a connection between the variations in the Gulf Stream currents and the weather in Europe. He proposed that ships might monitor the currents in the Stream near America and make the changes known in England in advance of the arrival of the climate-influencing warm water.

Although it is now commonly believed that the Gulf Stream is responsible for keeping the European climate mild, it is also important to consider the effect of the huge pool of warm water located in the middle of the North Atlantic gyre, the Sargasso Sea. In 1940, Columbus O'Donnell Iselin proposed that the warming of the European climate is least during times of increasing Gulf Stream transport. He based his theory on the fact that the processes which produce the warm Sargasso water are basically constant. As a result of the geostrophic relationship, an increase in the transport of the Gulf Stream would be accompanied by a depression of the thermocline in the Sargasso Sea. The overall effect would be to shrink the North Atlantic gyre. This would cause warm water to be drawn from the north, cooling the European climate.

It is also necessary to consider the importance of the warm southwest prevailing winds assisted by the low generated by the warm water to the west of Norway. These winds are warmed as they blow over the Gulf Steam. The ocean acts as a heat source and a stabilizer of temperature for the land.

A striking example of the climate influence of the Gulf Stream can be seen in the following photographs of Bouvet Island and Ireland. The two islands have approximately the same latitude, but are in different hemispheres. Bouvet Island is very cold and icebound. Ireland, on the other hand, has tropical palm trees. The difference in the vegetation is primarily due to the influence of the Gulf Stream and Sargasso Sea.

Above: Bouvet Island, South Atlantic

Below: Ireland, North Atlantic