Arctic climate variability is normal

It is well known that the present global warming is amplified in the Arctic and accompanied by unprecedented sea ice decline. Warm periods, like today, are associated with high northward heat transport, reduced growth of Arctic sea ice cover, and high surface air temperatures.

In a new study, researchers from the Bjerknes Centre for Climate Research in Bergen show the central role of the Barents Sea in Arctic climate change. The Barents Sea, located along the main pathway of Atlantic Water entering the Arctic, is important for creating variability in the entire Arctic air-ice-ocean system. As warm Atlantic Water flows through the Barents Sea, it loses heat to the Arctic atmosphere.

The paper demonstrates that voices using the increase in the Arctic sea-ice this summer compared to last year is not a foundation to call off global warming (e.g., the Daily Mail, the Daily Telegraph). Due to natural variability the scientists expect years and even decades with more sea-ice in the Artic than previous years. Even though this year’s ice-minimum is lower than last year’s it is still much lower than the “normal”, according to the National Snow & Ice Data Center.

Large ocean heat transport, less sea ice

Over the last years, Barents Sea ice has been substantially reduced due to a high Atlantic water heat transport. This explains the missing sea ice that has been observed in the last years. The specialty of the Barents region is that the ocean is controlling the sea ice variability, and not the heat fluxes forced by the atmosphere. The study is published in the acclaimed journal Reviews of Geophysics.

New model simulations show that in 2050 the Barents Sea is projected to be ice-free during the summer months with a surface temperature of about 4 degrees Celsius.

Natural variability

The Barents Sea is an area with pronounced climate oscillations, also when considering natural climate variability. E.g., there was a rather warm period in the 1950s, although not as warm as the present, and a colder period in the 1970s.

“The reason behind these variations between warm and cold periods is variations in the heat transport from south and internal feedbacks in the Barents Sea,” says Randi Ingvaldsen at the Institute of Marine Research (Havforskningsinstituttet).

Circulation changes cause cold winters

The heat release from the Barents Sea plays an important role in Arctic surface air temperature changes, influencing areas as far away as 60 °N. Previous studies suggested that the Barents heat also might perturb the large-scale atmospheric circulation leading into expansion of the Siberian High and possibly causing the recent European cold winters.

“New results from the Bjerknes Centre, however, show that the dynamics behind these cold winters are more complicated and that the natural climate variability plays an important role in creating the cooling anomalies,” says Svetlana Sorokina at the Nansen Center.

Sediments reveal importance of Barents Sea

Large air-ice-ocean variability is evident in proxy records based on sediments from the ocean floor or land that cover the last 2,500 years. These show that wind strength, ocean temperature and sea ice cover has changed over time frames of several hundred years, and indicate an important role of the Barents Sea in Northern Hemisphere climate variability over time.

“For example, from ca. 500 BC to ca. 700 AD the dominating climate responses were associated with weaker westerly winds than in the time period 700-2,000 AD,” says Bjørg Risebrobakken at Uni Climate.