Ice melting

The Norwegian Polar Institute has measured mass balance on the glaciers of Svalbard during the last 50 years. Annual measurements have been made on Midtre Lovenbreen and Austre Brøggerbreen since 1967. These are some of the longest time series available for Arctic glaciers. The studies of these glaciers have shown that there is a negative net mass balance. This indicates that the glaciers are decreasing in volume. It is assumed that this may be a result of the temperature increase that took place at the beginning of the 1900s.

Glacier in Svalbard. Photo: Stein Nilsen (The Norwegian Polar Institute)

The extent and thickness of the sea ice are decreasing

A large proportion of the Arctic Ocean is covered by ice throughout the year. Ice covers approximately 6 million km² in September and approximately 14 million km² in April-May. The extent of the sea ice between Iceland and Novaya Zemlya has decreased by approximately 33 per cent during the last 135 years. The decrease in the fall that the ice-covered area is particularly marked in autumns. In the period 1920-1998 the extent of the ice in the Barents Sea decreased by approximately 12 per cent in April and close to 40 per cent in August. This indicates that the rising spring and summer temperatures have most impact on the extent of the sea ice. The average annual reduction rate is currently stabilizing, from 8000 km² per year in 1880 to 3000 km² per year in 1980.

There have also been suggestions that the thickness of the sea ice is decreasing. According to some scientists the ice may have become as much as 40 per cent thinner during the last 20 to 40 years. There is, however, a close correlation between ice thickness and winter temperature, and since the temperature of the Arctic Ocean itself has not changed significantly in the last 40 years, this indicates that the changes in the thickness of the ice may not have been so large during this period. Variations in the average annual thickness may be as large as 0.9 meters. Longer time series are needed to draw definite conclusions on whether the thickness of the ice is changing.

Changes in the ocean circulation patterns

Ocean circulation patterns in the Nordic seas are controlled by the relatively warm water (7-9ºC) of the Norwegian Atlantic Current (extension of the Gulf Stream), and the relatively cold fresh water of the East Greenland Current originating in the Arctic Ocean, which is -2 to 0ºC. Most of the sea ice in the Arctic Ocean is exported southwards by the East Greenland Current through the Fram Strait.

The formation of bottom water in the Arctic Ocean and the Greenland Sea may be an important driving force for the Norwegian Atlantic Current. When seawater freezes the salt is separated out. Combined with the cooling of the water this makes the water heavier so that it sinks to the bottom. The bottom water that is formed flows towards the south in the deep ocean. This water has to be replaced by new water at the surface, and it has been suggested that this can be an important driving force behind the transport of warm North Atlantic Current water into the Nordic seas.

If this is the case, it would be expected that if the formation of bottom water in the Greenland Sea stops or slows down, this could lead to a significant decrease in the amount of Atlantic water flowing northwards, and as a result lead to dramatic cooling of the climate in our region. There is, however, nothing in current observations that indicates such a correlation. During the 1900s, bottom water formation in the Greenland Sea has decreased. At the same time the ice cover in the Arctic Ocean has also decreased, partly as a result of warming of the Atlantic water masses flowing into the Arctic Ocean. This again indicates that heat transport in the Atlantic Current is currently increasing. The Atlantic water masses in the Arctic Ocean are warming up more strongly than we have ever observed before, and it is uncertain whether this is a result of natural fluctuations or of climate change.

Wind direction and wind force affect the extent of the ice

The extent of the sea ice varies depending on the strength and direction of the wind over the Barents Sea. There has been a marked decrease in the air pressure over the Barents Sea since 1966, and since 1970 an increase in warm southerly winds has been observed. Low-pressure systems in the Barents Sea bring southerly winds over the Nordic Seas, which in turn leads to a reduction in the extent of the sea ice. The ocean circulation patterns are also to a certain degree driven by the winds, and fluctuate according to the atmospheric pressure systems.

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