After a spring season of more typical ice extent reports, Arctic ice is back in near-record territory. Today’s ice extent is just a few days behind the rapid spring ice melts seen in 2005–2007.
It is important that Arctic ice has not declined as much in spring as in the other three seasons. In late winter and early spring, the sun in shining on most of the Arctic ice, and ice reflects the sunlight much better than sea water does. If the ice is covered with a thin layer of snow, it reflects better still. Reflecting the sunlight back out into space slows the Arctic region’s warming trend.
The slower decline of Arctic ice in spring is consistent with measurements showing thin ice. Thinner ice breaks more easily and is more mobile. This allows ice to spread out from the areas where it forms. In April, the cold weather allows this ice to accumulate in places where it is not quite cold enough for ice to form. For example, ice that formed at the north end of Baffin Bay drifted southward and accumulated along the Labrador coast. But the ice at Labrador melted away in May. By June, this same dispersal effect reduces the ice area. When ice breaks, the new edges start to melt away, and any ice that drifts off on its own tends to melt quickly.
Climate models predict that summer Arctic ice will mostly disappear between 2040 and 2100. The climate models, though, track Arctic ice only up to about 1998; they fail to account for the rapid decline in Arctic ice since then. A naive extrapolation of ice trends for the past 13 years suggests that the sunnier months could be free of ice, at least in the open ocean, much sooner than that. The model that fits the recent experience most closely says it could happen around 2016. Significantly, this model suggests that May will be one of the months that will be ice-free. If the ice in spring keeps getting thinner, eventually, it will have to melt through.