The sea ice extent in the Barents Sea was back to normal this winter. A paradox? Actually not.
This text was published in Aftenposten (online and print) 23 April 2019.
Northeast in the Barents Sea, more than 400 kilometers north of the Finnmark coast, the Petroleum Safety Authority Norway has given permission to Equinor to drill the exploration well Korpfjell. This is the northernmost license ever given on the Norwegian continental shelf. For the last years, the well has been in safe distance from the sea ice edge.
But what happens with Korpfjell and other maritime activity in the Barents Sea if the sea ice expands towards the south? This is not entirely unthinkable.
Sea ice extent at its maximum
The sea ice reaches its maximum extent in March. This year, sea ice in the Barents Sea was back to its normal extent from the eighties and nineties, and in the western Barents Sea the ice edge stretched all the way down to Bjørnøya.
It may sound surprising that the sea ice has been increasing the last years, despite a continuously warmer global climate, but for scientists like myself this is not unexpected. Our research shows that even if the ice edge has moved gradually north and away from Korpfjell the last few years, the ice cover can increase periodically and again move south.
In the same way as the global temperature rises steadily although some years may be colder or warmer, the sea ice extent varies a lot from year to year even if the ice in the big picture decreases.
Man-made climate change is the main reason for the decreasing ice, but our research shows that natural climate variations may lead to years with increasing ice. Existing and future activity in the Barents Sea must therefore consider significant variations in ice cover from year to year, and from decade to decade.
Crucial ocean current
Why does the ice extent vary so much from year to year? One answer is the Gulf Stream, or the Norwegian Atlantic current as scientists call it. The ocean current transports large amounts of warm water and nutrients from southern latitudes and contributes to the Norwegian coast and the southern Barents Sea being ice-free and full of life. When the Atlantic current changes between warmer and colder conditions, the ice edge draws northwards and southwards, respectively.
Over the past few decades, the temperature of the Atlantic current has increased. Some of this warming is due to the general global warming, but much is also due to natural variations. Natural fluctuations in the sea and the effect of global warming have been combined, leading to considerably more heat in the Atlantic current and a greatly reduced ice cover in the Barents Sea.
The illustration shows the extent of the Arctic sea ice in March 2019. The orange line shows the average ice edge in the period 1981–2010. NSIDC / NASA Earth Observatory
On the other hand, if natural variations in the climate system had moved the ice edge in the opposite direction, we would probably have had little or no decline in the sea ice cover in recent years, despite global warming. It is therefore important to understand how and how much natural sea temperature fluctuations affect sea ice in order to predict its future development.
A predicted increase
We have previously shown that there is a time lag between changes in the Atlantic current and the ice in the Barents Sea. It is thus possible to make a prediction – a warning – about future changes in the ice cover based on the state of the sea today. Based on a weaker and colder Atlantic current in recent years, our warning in 2015 was that there would be more ice in the Barents Sea in the next winters, a warning that proved to be correct.
The ice edge of the future
But what will happen to the ice edge and the Atlantic current over the next 100 years? Results from 40 different climate model simulations show that the ocean circulation in the North Atlantic Sea is weakening towards the year 2100, but at the same time the Norwegian Atlantic current is strengthened, bringing more warm currents northwards towards the Arctic.
As the atmosphere also gradually warms up by increased CO₂ emissions, this leads to the sea ice in the Barents Sea slowly but surely disappearing. At the same time, our results show that in the future it is still possible to have ten-year periods with increasing ice cover due to changes in the Atlantic flow.
Our research thus shows that changes in the Atlantic current are important for the sea ice in the Arctic, both for the development over the next few years and for its final fate up to the year 2100. In order to understand and predict climate change in the Arctic, and be able to manage the area properly, it is important that continuous observations of the Atlantic current continue.