Sea ice in the Arctic Ocean has fallen to the lowest recorded level for the winter season, according to US scientists.
The maximum this year was 14.5 million sq km, said the National Snow and Ice Data Center at the University of Colorado in Boulder.
This is the lowest since 1979, when satellite records began.
A recent study found that Arctic sea ice had thinned by 65% between 1975 and 2012.
Bob Ward of the Grantham Research Institute on Climate Change and the Environment at the London School of Economics said: "The gradual disappearance of ice at the poles is having profound consequences for people, animals and plants in the polar regions, as well as around the world, through sea level rise."
The National Snow and Ice Data Center (NSIDC) said the maximum level of sea ice for winter was reached this year on 25 February and the ice was now beginning to melt as the Arctic moved into spring.
The amount measured at the end of February is 130,000 sq km below the previous record winter low, measured in 2011.
An unusually warm February in parts of Alaska and Russia may have contributed to the dwindling sea ice, scientists believe.
Researchers will provide the monthly average data for March in early April, which is viewed as a better indicator of climate effects.
Nasa scientist Walt Meier said: "The amount of ice at the maximum is a function of not only the state of the climate but also ephemeral and often local weather conditions.
"The monthly value smoothes out these weather effects and so is a better reflection of climate effects."
Analysis by David Shukman, Science editor, BBC News
The Arctic Ocean freezes every winter and much of the sea-ice then thaws every summer, and that process will continue whatever happens with climate change. Even if the Arctic continues to be one of the fastest-warming regions of the world, it will always be plunged into bitterly cold polar dark every winter. And year-by-year, for all kinds of natural reasons, there's huge variety of the state of the ice.
So what does this new record for the lowest level of winter ice actually mean?
For a start, it does not automatically follow that a record amount of ice will melt this summer. More important for determining the size of the annual thaw is the state of the weather as the midnight sun approaches and temperatures rise. But over the more than 30 years of satellite records, scientists have observed a clear pattern of decline, decade-by-decade.
So at some point this century the summers are on course to be clear of ice, opening up new shipping lanes, making it easier to access the region's oil and gas and possibly also altering the path of the jet stream that drives our weather. So the matter of when all this might happen is the subject of intense research.
Meanwhile, at the other end of the world, researchers are puzzling over the growth of sea-ice around parts of Antarctica. Overall, there is a fall in the global total of sea-ice but with lots of questions about its pace.
Commenting on the data, Alexander Shestakov, director of the WWF Global Arctic Programme, said: "This is not a record to be proud of.
"Low sea ice can create a series of reactions that further threaten the Arctic and the rest of the globe."