Northern Hemisphere Sea Ice Extent 2nd Lowest on Record

Northern Hemisphere Sea Ice Extent 2^nd Lowest on Record

Fig. 1: Northern hemisphere sea ice extent for September 2020 compared to all years back to 1978.

Discussion: The northern hemisphere sea ice extent ranks 2^nd lowest on record for the September 2020 (Fig. 1). The only year in which northern hemisphere sea ice was less abundant was 2012. The lack of sea ice does not mean that winter ahead will be warm. As the northern latitudes turn much colder during autumn and into early winter the widespread open water south of the polar ice cap acts as a moisture source for advection snows (i.e. cold winds blowing across open relatively mild water surface). Consequently, the northern latitudes of most, if not all continents gain above normal snowfall leading into calendar winter. In 2012 the November northern hemisphere snow cover expanse ranked 9^th highest (given the 1966-2020 climatology). In December 2012 the northern hemisphere observed the largest snow cover extent on record. The extent of snow cover eased in January 2013 ranking 21^st in the 54 year history returning to 7^th snowiest in February 2013. The November 2012 to February 2013 temperature anomalies featured very cold temperatures in Western Canada with frigid conditions in Central Russia (Fig. 2). Nowadays snow cover is needed to produce a cold risk. The constricted polar ice cap heading toward winter increases the risk of a larger than normal northern hemisphere snow cover heading into winter.

Fig. 2: The NOV-12 to FEB-13 northern hemisphere temperature anomalies are indicated.