Changes in the Arctic Ocean are so profound that the region is entering what amounts to 'a new era', according to Norwegian scientists.
A switch from a permanent cover of thick ice to a new state where thinner ice vanishes in the summer will have far-reaching implications, they say.
The Norwegian Polar Institute has been mounting an expedition to the Arctic Ocean during the year's coldest months.
Scientists have to brave extreme temperatures and total darkness.
Their aim is to gather data on the condition of the ice as it freezes during the polar winter.
A research vessel, the Lance, has been deployed to an area about 500 miles from the North Pole and allowed to drift with the pack-ice.
The director of the institute, Jan-Gunnar Winther, said that measuring what happens in the winter was vital to improving scenarios for future climate change.
'We have almost no data from the Arctic Ocean in winter - with few exceptions - so this information is very important to be able understand the processes when the ice is freezing in early winter and we'll also stay here when it melts in the summer,' he explained.
'A new era has entered, we are going from old ice to young ice, thinner ice and the climate models used today have not captured this new regime or ice situation.
'So knowing how it is today can improve climate models which again improve the projection for global climate change.&.