The Bjerknes Centre is a collaboration on climate research, between the University of Bergen, NORCE, the Institute of Marine Research, Nansen Environmental and Remote Sensing Centre.

Jakob Dörr looking over Bergen. (Foto: Jakob Dörr)

The Ever Moving Sea Ice 

The Arctic sea ice is on the move all year. It expands to its maximum during March and reaches its minimum in September. The variation during the year, and from year to year, depends on wind, weather and ocean currents. But the Arctic is changing.  

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“Over the last few decades the sea ice has slowly been disappearing. The loss is especially strong in the Barents Sea, where almost half of the sea ice the last 40 years has disappeared”, says Jakob Dörr says in the video. 

Jakob Dörr is a PhD student in the Nansen Legacy, a large Norwegian research project aiming to understand the Barents Sea. 

Ice, atmosphere and ocean 

At the Geophysical institute, UiB and the Bjerknes Centre for Climate Research, Jakob Dörr is connected to a research group studying the how the ice edge varies and how to predict it. 

For his PhD thesis, he is studying the natural variability of the sea ice – how much the sea ice varies. Some years, the sea ice disappears quickly. Other years and periods, the sea ice is expanding. This is due to the interaction between the atmosphere and the ocean. 

The North Atlantic Current brings heat northwards all the way from the Mexican Gulf, entering the Barents Sea. How much heat this current transports, and the intensity of the ocean currents, varies from year to year ? 

The atmosphere transports warm or cold air masses, and the strength and direction of the winds moves the sea ice around. Southerly winds in the Barents Sea will, for example, push the ice northwards. These movements can go very quickly. 

Sea ice area in the Barents sea. The most recent data point here is March 2020. (Ill. Jakob Dörr)
Sea ice area in the Barents sea. The most recent data point here is March 2020. (Ill. Jakob Dörr)

Modelling experiments 

To understand how much these natural variations affect the sea ice, Dörr and his colleagues use climate models. The climate model simulates the different components of the natural climate system, including the amount of sea ice.

When running the models over and over again, they can estimate the natural variations of the sea ice. 

“By adding slight changes for every run, we get a view of how much the amount of sea ice varies. Individually, the model runs are not correct, but by putting together we can learn much about the variability, and about the long-term trend,” Dörr says. 

And even though the amount of sea ice goes up and down depending on the year and season, the overall trend is downwards. The Arctic sea ice is disappearing, both in summer and winter. 

According to Jakob Dörr and his colleagues, the downward trend is too big to be caused by the natural variations, and the ongoing global warming is the likely explanation. However, due to the natural variability, we can still expect occasional inceases in the sea ice, Dörr adds. For example, over the last four years the amount of sea ice during winter in the Barents Sea has increased again, due to the record low in 2016. 

Isdekket i Barentshavet. (Foto: Marius Årthun)
Isdekket i Barentshavet. (Foto: Marius Årthun)