In early September of 2016, the National Snow and Ice Data Center declared that sea ice in the Arctic Ocean had reached its lowest point in its area of coverage (“extent”) for the year, and that this low point was the second lowest on record, beaten only by the ice extent of 2012. The following graph from the National Snow and Ice Data Center shows the average extent of sea ice for each of the days of the months of July through November during the years 1981-2010. The ice extent of the last five years — 2012, 2013, 2014, 2015 and 2016 — are displayed singly in comparison to the 1981-2010 average:
As this graph shows, the extent of ice in the Arctic Ocean during each of the last five years has fallen well below the 1981-2010 average. Any one year’s deviation might be thought of as weather. A pattern of change over many years is a climate trend. During the last two years of 2015 and 2016, the Arctic sea ice extent fell more than two standard deviations below the 1981-2010 average, meeting the standard for a statistically as well as substantively significant difference.
For most of the year, the extent of ice in the Arctic Ocean has remained far below the 1981-2010 average, but above the drastically low daily readings of 2012. In an alarming turnabout, over the last month levels of Arctic sea ice have been hitting record low marks on a daily basis. The Arctic’s sea ice is growing during the early winter months, as typically happens during each Arctic winter. But the record low rate of growth suggests the possibility that Arctic ice will start the year at a weaker point than in previous years, favoring an accelerated loss of growth in the summer to come.