To the scientists' surprise, Greenland's largest glacier has grown while everyone around it is melting.
Since 2016, ice from the Jakobshavn glacier has become somewhat dense, countering the seemingly relentless withdrawal of all polar ice, NASA experts have found.
But they say their findings are not good news for climate change because Greenland continues to lose large amounts of ice, far outweighing the small amount collected by the Jakobshavn glacier.
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In an article in Natural GeosciencesResearchers at NASA's Oceans Melting Greenland (OMG) project said the small growth was due to relatively cool ocean waters at the base of the glacier, reversing a 20-year trend of thinning and retreating ice.
But Jakobshavn drains only about 7 percent of the ice sheet, so even if it were growing robustly, the loss of ice elsewhere would outweigh its small expansion, scientists warn.
"The thought was once the glaciers begin to recede, nothing prevents them," said Josh Willis, the project's chief scientist. "We have found that this is not true."
Researchers believe that a recent influx of exceptionally cold North Atlantic water, pushing the Arctic, has made the glacier grow slightly.
And other glaciers in Greenland's 200 or so may also be expanding, suggesting that the changes may be more difficult to predict than previously thought, Willis said.
A natural cycle in the Atlantic Ocean alternates between hot and cold once every 20 years, bringing cooler waters to the west coast of Greenland. But the phase will change again at some point and the warmer waters will return.
"All this is an indicator of how glaciers are sensitive to ocean temperatures," says the study's lead author, Ala Khazendar, a glaciologist for the project.
The team suspects this may mean that the overall melting trend may be happening more slowly than previously thought, according to National Geographic.
However, the glacier Jakobshavn "is still contributing to the global rise of the sea," said Khazendar. "That does not stop."
Between 2000 and 2010, Jakobshavn contributed the largest solid ice discharge across Greenland's ice sheet, equivalent to almost 1mm of the global sea's rise.
The glacier had periods of accelerated retreat and growth in the 20th century, said Dr. Khazendar.
But, on average, the air and sea are heating up, so the retreats will always outweigh the breakthroughs, Dr. Willis added.
"More than 90% of the heat that is trapped by greenhouse gases is warming the oceans. So in the long run we know that this cooling will pass. When that happens, the glacier will retreat even faster than before. "
The Antarctic glaciers are also being corroded by hot currents, with retreat of 10% of the continent's coastal glaciers.
Research has shown that from 1979 to 2012, Greenland's rains increased, causing the sudden melting.