Greenland Ice Sheet

The loss of Arctic sea ice could trigger enormous additional global warming

By Adam Vaughan

The Greenland ice sheet

Alireza Teimoury / Alamy

If the Arctic sea ice is expected to disappear in summer by the middle of the century, the world could see a vicious cycle fueling global warming so much that the effects of China's carbon neutrality are all but wiped out.

It is known that ice losses in frozen regions trigger “climate feedback loops”. For example, white ice reflects much of the sun's energy. So when it is replaced with dark open water that absorbs heat, more warming occurs. But how much more warming is an open question.

To answer this, Ricarda Winkelmann from the Potsdam Institute for Climate Impact Research in Germany and her colleagues modeled the effects of such feedback on global temperature rise when ice disappeared in summer from mountain glaciers, the ice sheets of Greenland and West Antarctica, and the Arctic. They found that the loss of ice in all four locations would lead to an additional global warming of 0.43 ° C for centuries to millennia if the temperature of the world rose to 1.5 ° C.

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Arctic feedback, however, could lead to warming on much shorter time scales. Summers in the region are expected to be ice-free before 2050. This means that by the middle of the century, the Arctic alone could cause an additional 0.19 ° C of global warming on top of 1.5 ° C. A fifth of a degree is a large number: China's recent commitment to become climate neutral by 2060 is expected to reduce global warming by 0.2 to 0.3 ° C.

The feedback in the Arctic would have an even greater local impact, raising temperatures by 1.5 ° C in a region that is warming faster than the rest of the world and is hit by record fires.

“The ice masses on earth are important. It is in our hands what happens to the ice masses and what in turn affects our global climate, ”says Winkelmann. The team used computer simulations of Earth systems to quantify the feedback that would result from the total loss of ice – a dramatic scenario that could be averted if humanity curbs emissions.

Changes in reflectivity or albedo accounted for 55 percent of the 0.43 ° C warming. Feedback also included water vapor, which contributed 30 percent to warming – warmer air can hold more water and trap more heat in the atmosphere. Clouds contributed 15 percent.

Winkelmann says that while the 0.43 ° C total warming would not be immediate, human emissions are putting ice sheets like Greenland and West Antarctica at irreversible tipping points, meaning action is important today. "Decisions that we make in the next few years can determine the fate of the earth's ice masses in the long term," she says.

Kim Holmén of the Norwegian Polar Institute says, "A clever use of models to quantify the contribution of various feedbacks to ultimate warming."

Journal reference: Nature Communications, DOI: 10.1038 / s41467-020-18934-3

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