Status table sea ice metrics

Explanation for how the sea-ice metrics are calculated:


1. Change in date of spring sea-ice retreat and change in date of fall sea-ice advance (days per decade) over the period 1979-2018.  Every year, the area of sea ice reaches a maximum in March and a minimum in September.  To measure the timing of the seasonal change in sea ice, we find the date each spring when the area of sea ice has dropped to a specific threshold, and the date each fall when the area has grown back to that same threshold.  The region-specific threshold is halfway (50%) between the mean March sea-ice area and the mean September sea-ice area, where the means are calculated over the 30-year reference period 1981-2010.

2.  Change in summer sea-ice area (percent change per decade) over the period 1979-2018, relative to the average summer sea-ice area during the 30-year reference period 1981-2010.  Summer is defined as June 1 – October 31.

Further reading:

Stern, H.L., and K.L. Laidre, 2016, Sea-ice indicators of polar bear habitat, The Cryosphere, 10, 2027–2041, doi:10.5194/tc-10-2027-2016,
https://www.the-cryosphere.net/10/2027/2016/