The Washington PostDemocracy Dies in Darkness

Opinion The Arctic’s ice is thinning faster than expected. It’s an ominous sign.

A polar bear dries off after swimming in the Chukchi Sea in Alaska on June 15, 2014.
A polar bear dries off after swimming in the Chukchi Sea in Alaska on June 15, 2014. (Brian Battaile/AP)
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POLAR BEARS struggling on thin Arctic ice is perhaps the most iconic image associated with climate change. Human-caused global warming is extreme near the poles, where the temperature is rising much faster than elsewhere. The result is not just the loss of polar bear habitat, but also dangerous disruption of the climate system. Now a group of British scientists has concluded that the Arctic’s coastal sea ice is thinning much faster than experts had previously estimated.

Melting land-based ice, huge quantities of which comprise the ice sheets on Antarctica and Greenland, threatens to raise global sea levels over time, as water stockpiled on land flows into the sea. Recent research suggests this process is happening at an alarming rate and may threaten human society sooner than previously thought. By contrast, sea-based ice, like that which covers Arctic areas such as the North Pole, already contributes to the volume of the oceans, because it floats in the water like ice cubes in a cup. But the thinning of sea ice in coastal Arctic regions is an ominous sign for other reasons.

“The thickness of sea ice is a sensitive indicator of the health of the Arctic,” said Robbie Mallett, one of the University College London researchers behind the new study. “It is important as thicker ice acts as an insulating blanket, stopping the ocean from warming up the atmosphere in winter, and protecting the ocean from the sunshine in summer.” That second point is key: Thick sea ice reflects sunlight away from the planet and allows less solar radiation to reach the water underneath; losing lots of it means more heat gets trapped there. This is just one of many climate “feedbacks” in which warming induces effects that result in faster warming.

It turns out that warming can also scramble scientists’ efforts to measure how the planet is changing. Scientists’ previous estimates of Arctic sea ice relied on satellite measurements combined with estimates of how much snow accumulated on top of the ice. The more weight on top of the ice, the more ice sinks below the surface. But the snow estimates are two decades old, and global warming has changed the picture over that period. “Because sea ice has begun forming later and later in the year, the snow on top has less time to accumulate,” Mr. Mallett explained. “Our calculations account for this declining snow depth for the first time, and suggest the sea ice is thinning faster than we thought.”

The British team’s new calculations indicate that Arctic ice is thinning 70 to 100 percent faster — that is, at roughly double the rate — than previously thought. This finding is just another in a long string of warnings from scientists that many of global warming’s predicted effects may be occurring faster or in a more severe manner than anticipated.

Climate doubters often point to experts’ uncertainty about how bad climate change and its consequences could be, arguing that inaction might not be as irresponsible as scientists claim. But uncertainty works in both directions; global warming could be tamer than predicted — or far worse. Too many recent measurements have suggested that the consequences might land on the “far worse” side of the spectrum. The uncertainty should not comfort people — it should spur everyone to action.

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