The Arctic has ended the winter with record low sea ice cover after warm temperatures and "heat waves", US scientists said.
Arctic sea ice melts and regrows over the year, freezing throughout the winter months to reach a maximum extent in late February or March, then melting through the summer to hit a low point in early or mid-September.
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Maximum sea ice cover in early March, before the summer melt began, was at a record low for the third year in a row, scientists at the National Snow and Ice Data Centre (NSIDC) and Nasa said.
The extent of ice in the Arctic Ocean at its maximum on March 7 was 14.42 million square kilometres (5.57 million square miles), the lowest in the 38-year satellite record, and below previous records in 2016 and 2015.
A very warm autumn and winter contributed to the low levels of ice, with air temperatures 2.5C above average over the Arctic Ocean.
General warmth in the region during the winter was punctuated by a series of extreme heat waves over the Arctic Ocean, the scientists said.
The lack of ice cover at this time of the year could mean 2017 sees record low sea ice conditions in the Arctic by the end of the summer melting season.
Julienne Stroeve, NSIDC scientist and professor of polar observation and modelling at University College London, said: "Such thin ice going into the melt season sets us up for the possibility of record low sea ice conditions this September."
Ted Scambos, NSIDC lead scientist, said: "Thin ice and beset by warm weather - not a good way to begin the melt season."
Nasa scientist Walt Meier said that while the Arctic maximum is not as important as the seasonal minimum in September, the long-term decline in ice cover is a clear indicator of climate change.