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The seasonal sea-ice retreat across the Arctic Ocean is perhaps one of the most conspicuous indicators of climate change. In September 2012, a new record was set for the time that we have been tracking sea ice with satellites: the minimum sea ice extent was some 50% below the climatic average for that month. Four years on, and the September 2016 record tied with 2007 for the second lowest sea ice extent since measurements began in 1978.
The seasonal retreat of sea ice is largely because the atmosphere in the Arctic is heated under 24
