Photo: Sebastian Garland (The Norwegian Polar Institute)
Temperatures are rising and the ice is melting
Three distinct periods of temperature change have been observed in the Norwegian terrestrial Arctic during the last century. Until the 1940s there was a significant rise in temperature, followed by a slight drop from the 1940s to the 1960s. Since the 1960s the temperatures have risen again, particular during spring.
Glaciers and the extent of the sea ice shrinking
The glaciers in Svalbard 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.
The extent of the sea ice between Iceland and Novaya Zemlya has decreased by approximately 33 per cent over the last 135 years. The average annual reduction rate is currently stabilizing. The reduction in the extent of the ice is most evident during autumn. This indicates that it is changes in the spring and summer temperatures that affect the sea ice extent most. There have been suggestions that the thickness of the sea ice is also decreasing. However, more measurements over a longer time period are necessary to document such changes.
Ocean circulation patterns are affected
Ocean circulation patterns in the Nordic seas are controlled by the relatively warm water of the Gulf Stream and the relatively cold and fresh water of the East Greenland Current originating in the Arctic Ocean.
Most of the sea ice of the Arctic Ocean is exported southwards with the East Greenland Current. The Greenland Sea has long been known as an important area for deep-water formation, which may be an important driving force for the Norwegian Atlantic Current. When water sinks during the process of deep-water formation, it must be replaced by surface water, which is transported in with the North Atlantic Drift.
Climate changes could affect the deep-water formation process and the ocean circulation patterns, and thereby lead to additional changes in the extent of the sea ice and the climate of the polar regions of Europe.
The Gulf Stream could be weakened
Paradoxically, a general global warming may result in a cooler climate in our part of the world. The reason behind this is that reduction of the deep-water formation process could reduce the strength of the Gulf Stream.
The existence of the Gulf Stream is the reason why temperatures are 5-8°C higher in our region than at comparable latitudes elsewhere. Sediment cores from the ocean floor show that during and immediately after the last ice age, there were large, rapid temperature changes in our region. It has been estimated that there was a change of 5-7°C over 10-100 years. This could indicate that the formation of deep water has stopped, for example in periods when melting processes were at a peak. It is uncertain whether we can expect such changes due to the global warming now being experienced.
While an ice surface covered by snow absorbs 10-20 per cent of the solar radiation, ice-free water absorbs as much as 90 per cent of this radiation. This leads to warming and increased evaporation. A change in the extent of the ice cover in the oceans would therefore affect surface temperatures. This is an example of positive feedback: An increase in the absorption of solar radiation leads to higher temperatures and an accelerating melting rate, which in turn results in more open water which can absorb more solar radiation.
Human impact on temperatures
Greenhouse gasses in the atmosphere absorb heat from the earth, and are important in maintaining the temperature balance in the atmosphere. Greenhouse gas concentrations in the atmosphere are increasing as a result of emissions from human activities, which contribute to a rise in mean temperatures and global climate change. The extent of the changes will vary from region to region, but will also affect the polar regions. Most climate models today indicate increased warming in the polar regions. Extensive research is now in progress to increase our understanding of the potential consequences of higher temperatures on the overall climate system.
A better understanding is necessary
Since the future consequences of global warming in the northern regions is still very uncertain, it is important to improve the understanding of the climate system in the region. Long-term monitoring of the situation is important, and we must continue to collect data on the changes in the extent of the sea ice, ocean circulation patterns, the radiation balance and the mass balance of glaciers. It is also important to increase our understanding of energy exchange and feedback mechanisms between the atmosphere, the sea ice and the ocean.
Regional climate models will be useful in evaluating the consequences of different climate scenarios. They may also be useful in resource management, e.g. as a tool for assessing the impact of sea ice on the fisheries or changes to the vegetation cover in Svalbard.