New data shows peak sea ice cover this year broke last year's record low. Scientists say while this is partly down to natural fluctuation, it fits a clear trend linked to global warming.
Rising Arctic temperatures this winter have contributed to a new record low for Arctic winter sea ice.
Maximum ice coverage this year, on March 24, was 1.12 million square kilometers (431,000 square miles) less than average – and 13,000 square kilometers (5,000 square miles) below last year's record low.
The measurements refer to the peak extent of winter sea ice coverage, before it begins to retreat during the spring and summer.
Arctic hotting up
"The record low in Arctic sea ice cover during this last winter is one of the symptoms and consequences of the ongoing global warming due to our greenhouse gas emissions," said Stefan Rahmstorf, head of Earth System Analysis at the Potsdam Institute for Climate Impact Research in Germany.
"Global temperatures have been steadily increasing now since at least the early 1970s."
Air temperatures over the Arctic Ocean in December, January and February were 2 to 6 degrees Celsius (4 to 11 degrees Fahrenheit) above average in nearly every region, according to the National Snow and Ice Data Center (NSIDC), which released the data this week.
Temperatures 12 degrees Celsius (22 degrees Fahrenheit) above average were recorded north of Svalbard in March.
"I've never seen such a warm, crazy winter in the Arctic," said Mark Serreze director of the NSIDC, in a press release. "The heat was relentless."
Warm waters from the Atlantic
Scientists said the high temperatures were probably partly due to the El Nino effect on the Pacific.
Arctic sea ice extent on March 24, 2016 averaged 14.52 million square kilometers, beating last year's record low of 14.54 million square kilometers
But the most dramatic loss of sea ice was on the Atlantic side of the Arctic – in the Barents and Kara Seas.
Tore Furevik, director of the Bjerknes Centre for Climate Research in Norway, said this was because warm sea currents from the Atlantic were primarily to blame for low winter sea ice cover.
"We have had very warm waters flowing into the Arctic from the north Atlantic during the last couple of years," Furevik told DW. "Part of this is likely related to global warming, but part is maybe also more natural fluctuation."
For this reason, winter sea ice cover is seen as a less reliable indicator of climate change than summer sea ice cover. But Furevik said climate change was undoubtedly a factor.
"Seeing that we have had a record low sea ice maximum last year and a new record low this year – that points to global warming. We shouldn't be surprised if next year we have more ice again, but the long term trend is evidently towards less sea ice."
Implications for weather systems
Loss of Arctic sea ice and resulting sea level rise have implications for weather systems.
"Of particular concern to us is the especially rapid warming of the Arctic during the past fifteen years," Rahmstorf told DW.
"This has caused accelerated loss of continental ice from Greenland, which raises sea level and likely contributed to a weakening of the Gulf Stream System. It possibly also affected the jet stream in the atmosphere and has been linked to extreme weather events in mid-latitudes."
Less sea ice cover means more heat can be absorbed and given off by the ocean. Furevik said research was being carried out into possible impacts of sea ice loss in Barents Sea on climatic systems to the east, including consequences for winter weather in places like China and Japan.
Dubious gains for fisheries
However, there are some winners as the north Atlantic warms up. Reduced ice cover and warmer waters have resulted in a considerable boost for fisheries, Furevik said.
"The amount of cod now off the northern coast of Norway and the Barents Sea seems to be larger than ever before. So that's a very positive impact for the economy of northern Norway."
Still, Greenpeacehas warned
that fishing in the Arctic poses a threat to wider biodiversity in the region.