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 Mallet, 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.
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.