The Long, Troubling Decline of Arctic Sea Ice
Throughout 2020, the Arctic Ocean and surrounding seas endured several notable weather and climate events. In spring, a persistent heatwave over Siberiaprovoked the rapid melting of sea ice in the East Siberian and Laptev Seas. By the end of summer, Arctic Ocean ice cover melted back to the second-lowest minimum extent on record. In autumn, the annual freeze-up of sea ice got off to a late and sluggish start.
But any single month, season, or even year, is just a snapshot in time. The long view is more telling, and it is troubling.
Forty years of satellite data show that 2020 was just the latest in a decades-long decline of Arctic sea ice. In a review of scientific literature, polar scientists Julienne Stroeve and Dirk Notz outlined some of these changes: In addition to shrinking ice cover, melting seasons are getting longer and sea ice is losing its longevity.
The longer melting seasons are the result of increasingly earlier starts to spring melting and ever-later starts to freeze-up in autumn. The map above shows trends in the onset of freeze-up from 1979 through 2019. Averaged across the entire Arctic Ocean, freeze-up is happening about a week later per decade. That equates to nearly one month later since the start of the satellite record in 1979.
The change is part of a cycle called “ice-albedo feedback.” Open ocean water absorbs 90 percent of the Sun’s energy that falls on it; bright sea ice reflects 80 percent of it. With greater areas of the Arctic Ocean exposed to solar energy early in the season, more heat can be absorbed—a pattern that reinforces melting. Until that heat escapes to the atmosphere, sea ice cannot regrow.