Arctic sea ice shrinks to second-lowest summer extent since the beginning of satellite observation

This summer, for the second time in the 42-year history of satellite-based sea-ice observation, the Arctic sea ice shrank to less than 4 million square kilometres. Judging from the latest satellite images, by the end of the second week of September, the remaining ice only covered an area of 3.8 million square kilometres. The only time there’s been less ice was in the record year of 2012. Back then, according to data from the University of Bremen, what is referred to as the September sea-ice minimum was only 3.27 million square kilometres. 

Yet this massive loss of ice hardly came as a surprise to the majority of observers, for two main reasons. Firstly, last winter an unusually high percentage of thin sea ice was formed in Russia’s marginal seas of the Arctic Ocean, because constant offshore winds rapidly swept the young ice to the north. As a result, the ice cover on the Laptev, Kara and East Siberian Seas remained comparatively thin and broke up again in March – earlier than ever before. 

Secondly, this year the Arctic chiefly stood out for its record high temperatures. In May and June a large warm-air cell lingered over the Siberian coast, pushing air temperatures as much as 6 degrees Celsius above the long-term average. “This heat first melted the thin sea ice in the Laptev Sea; then it accelerated the ice retreat in the East Siberian Sea. As a result, by June the Russian Arctic contained roughly one million square kilometres less sea ice than in the past seven years,” explains Prof Christian Haas, Head of the Sea Ice Physics Section at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Bremerhaven.

In July, another warm-air cell made its way into the Central Arctic, causing temperatures to climb as much as 6 degrees Celsius over the long-term average for the years 1981 to 2010. In the same month, a storm swept over the Canadian sector of the Arctic Ocean, scattering the sea ice floating there. Afterwards, many of the floes melted as the patches of open water surrounding them were soon warmed by the sun.

Unusually warm water

But this year, the growing amount of heat in the Earth’s climate system also affected the sea ice from below. In those areas where the sea-ice cover disappeared early in the year, the ocean’s dark surface had much more time to absorb solar energy. Consequently, the surface water experienced intense warming. Surface temperatures in Russia’s marginal seas, the Barents Sea and the Chukchi Sea rose to as much as 4.5 degrees Celsius over the long-term average. “We believe that due to the stable high-pressure cell over the Central Arctic in July and August there were far more cloudless days. Therefore, as a result, the solar radiation which is normally buffered by clouds was an additional factor in this year’s melting,” explains AWI climatologist Dr Monica Ionita.

Most likely, heat from the ocean’s depths was also a factor. As the latest research shows, in the eastern part of the Arctic Ocean, warm Atlantic water masses which previously circulated at a depth below 150 metres are now gradually rising, producing changes in, e.g., the heat transfer between the water and ice. Under these conditions, even in winter, heat from deeper layers can rise to the surface more frequently, melting the ice from below and slowing its growth. As a result, at the end of this winter the ice was thinner than it had been in past decades.

Eyewitnesses of the rapid sea-ice retreat

This summer, the experts on board the German research icebreaker Polarstern had front-row seats for the rapid melting. “The scale of Arctic sea-ice retreat this year was breath-taking. Just a short time ago, when we reached the North Pole, we could see broad stretches of open water reaching nearly to the Pole, surrounded by ice that was riddled with holes produced by massive melting. The Arctic ice is disappearing at a dramatic rate. With the MOSAiC expedition, we’re investigating the underlying processes on site, and in more detail than ever before, so that we can accurately represent these rapid changes in the Arctic in our climate models,” says Expedition Leader Prof Markus Rex.

The exact time at which the sea ice reaches its absolute minimum depends on the weather conditions in the Arctic, and can only be determined once there is clear evidence that the sea-ice extent has begun to grow again. Based on past experience, this usually comes in mid-September, though sometimes not until the second half of the month.

Additional information for members of the press:

The Alfred Wegener Institute and the University of Bremen reported an Arctic sea ice minimum of less than 4 million square kilometers for 2019. As we now know, this information was not entirely correct due to an error in our processing routine for calculating the extent of the sea ice. We have now recalculated all values ​​from 2018: The corrected Arctic sea ice minimum for September 2019 is 4.24 million square kilometers. You can find out more about the identification of the error and the recalculation of the sea ice extent here: www.meereisportal.de/archiv/2020-kurzmektiven-vergleichtexte/neberechnung-ausdehnung/

You can find further information and charts on the development of the sea-ice situation in the Arctic at meereisportal.de.