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.

Sea ice at the southern point of Greenland, from ice2ice cruise to Tunulliarfik fjord in 2016. Photo: Jørund Raukleiv Strømsøe, NORCE and Bjerknes Centre.

Rapid warming in the Arctic when the sea ice withdraws

This summer has produced extreme melts on the Greenland ice and Arctic sea ice. The researchers of the ice2ice project sees parallels to prehistoric, extremely rapid changes in climate.

"We now know how the sea ice and the temperature over Greenland is connected, with an incredible degree of certainty. We can see that the changes in ice or no ice is like night and day for the climate in the Arctic," says Eystein Jansen, Professor at the University of Bergen (UiB) and the Bjerknes Centre for Climate Research.

He is one of the four project leaders in the large research project ice2ice. A cooperation over the past five years between four institutions in Copenhagen and Bergen has given many a groundbreaking insight. The researchers can now see clear connections between the current climate changes and sudden heating periods during the ice age.

Jansen and his colleagues think the warming we see today can be characterised as a sudden heating event when compared with earlier warm periods during the ice age. It has been known that in the ice age there were repeated, short climate fluctuations over many thousands of years.

Climate mysteries in the ice age

The heating events during the last ice age, was seen as a mystery when they were discovered around 40 years ago by Danish researcher WIlli Dansgaard.

What the researchers now know, is that these sudden heating periods occured after rapid withdrawals of sea ice. And they appear with reoccurring intervals of a couple of thousand years. During the last ice age large parts of Northern Europe was covered by a substantial ice shelf, while the sea ice in the Arctic and the Nordic Sea in the coldest periods reached the Bay of Biscaya. This lasted for around 80,000 years, yet the sea ice did have sudden withdrawal periods with following rapid heating in the areas around the North Atlantic Ocean, especially on Greenland.

In a period of only a few decades – in the middle of the ice age – the air above Greenland heated quickly (close to 15 degrees), and athmospheric temperatures remained warm for hundreds of years, before the ocean again was covered in ice.

"What is new is that we can draw a line from what happened under the ice age to what is happening today," says Jens Hesselbjerg Christensen, Professor at Niels Bohr Institute, at the University of Copenhagen.

"We have looked closer at the processes and found more about how they are connected, and now we have a much more complete picture of the context of sea ice and temperature in the air and Greenland melting periods. This means we can draw comparisons to the current situation," says Christensen.

He is a former climate research leader at the Danish Meteorological Institute, one of four partners in the ice2ice project. Christensen is a highly merited climate researcher and meteorologist who has been working mainly with climate modelling. In this project he has also participated in analysing data from sea and ice cores.

Ice or not – like night and day

"This year the Greenland melt season started extremely early, lasting throughout July," says Kerim Nisancioglu, Professor of climate dynamics at UiB and the Bjerknes Centre.

2012 was a gloomy year of records for the Arctic ice. Both on Greenland and in the sea, the ice melted to a minimum unrecorded for 8,000 years. As a consequence of the record-breaking year and the observations in the Arctic and Greenland, Nisancioglu and Jansen with UiB and Bjerknes Centre, Hesselbjerg-Christensen at DMI, and Bo Møllesøe Vinther at University of Copenhagen began to develop the ice2ice project. Funding through ERC came two years later.

Five years ago the researchers asked themselves what would happen if the Arctic sea ice disappeared. Today they have gathered a large number of answers.

"Today we have a better understanding of the rapid climate fluctuations occurring in the last ice age. Only now we can say that what we see in the data looks like what we see in the models. We have data to provide us with the entire picture," says Bo Møllesøe Vinther, Associate Professor at the Niels Bohr Institute, University of Copenhagen.