Even if global warming stopped today, the ice would keep shrinking.
25 Aug 2020 – Annual snowfall can no longer replenish the melted ice that flows into the ocean from Greenland’s glaciers. That is the conclusion of a new analysis of almost 40 years’ satellite data by researchers at Ohio State University. The ice loss, they think, is now so great that it has triggered an irreversible feedback loop: the sheet will keep melting, even if all climate-warming emissions are miraculously curtailed. This is bad news for coastal cities, given that Greenland boasts the largest ice sheet on the planet after Antarctica. Since 2000 its melting ice has contributed about a millimetre a year to rising sea levels. The loss of the entire ice sheet would raise them by more than seven metres, enough to reconfigure the majority of the world’s coastlines.
In the 1980s and 1990s, Greenland’s ice maintained a rough equilibrium. Each year the sheet lost some 400bn tonnes of ice in the summer—both by ice and snow melting on the surface, and the “discharge” of ice by glaciers losing chunks as they push out into the sea. This was replenished by a similar amount of fresh snow in the winter. But after 2000 the ice sheet began losing mass permanently. The amount that has disappeared is so huge that it has caused a noticeable change in the gravitational field over the island. It has also caused the glaciers to retreat by about 3km since 1985, exposing more of them to warmer ocean water. This has increased the rate of melting to the point where, even if the climate stopped getting hotter, more ice would be discharged each year than could be replaced, the scientists reckon. “The ice sheet is now in this new dynamic state, where even if we went back to a climate that was more like what we had 20 or 30 years ago, we would still be pretty quickly losing mass,” explains Ian Howar, one of the study’s authors.
Over the past three decades, the Arctic has warmed at least twice as fast as the rest of the world. This is because of a phenomenon known as Arctic amplification, in which higher concentrations of greenhouse gases produce larger increases in temperature at high latitudes. It also means that changes in the Arctic region are an important indicator of the progression and impacts of climate change. The decline of the Greenland ice sheet is a harbinger of things to come. “Greenland is going to be the canary in the coal mine,” says Mr Howar. “And the canary is pretty much dead at this point.”
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