The kilometers-thick ice sheet that covers Greenland saw a near-record imbalance last year between new snowfall and the discharge of meltwater and ice into the ocean, scientists have reported.
A net loss of 600 billion tonnes was enough to raise the global watermark 1.5 millimetres, about 40 percent of total sea-level rise in 2019.
The Greenland ice sheet — which, until the end of the 20th century accumulated as much mass as it shed — holds enough frozen water to lift the world’s oceans by seven meters.
Almost as alarming, however, as the ice sheet’s accelerating disintegration are the forces driving it, the authors reported this week in The Cryosphere, a peer-reviewed journal published by the European Geosciences Union.
More than half the dramatic loss in 2019 was due not to warmer-than-average air temperatures but rather unusual high-pressure weather systems linked to global warming.
These anticyclone conditions blocked the formation of clouds over southern Greenland, causing unfiltered sunlight to melt the ice sheet surface. Fewer clouds also meant less snow — 100 billion tons below the 1980-1999 average.
In addition, the lack of snowfall left exposed darkened, soot-covered ice which absorbs heat rather than reflecting it, as pristine white snow does.
Conditions were different, but no better in the northern and western parts of Greenland, due to warm, moist air pulled up from lower latitudes, the study showed.
All of these factors led to accelerated melting and runoff, creating torrential rivers cutting through the ice toward the sea.
“These atmospheric conditions are becoming more and more frequent over the past few decades,” said lead author Marco Tedesco, a scientist at Columbia University’s Lamont-Doherty Earth Observatory.
“This is very likely due to the ‘waviness’ in the jet stream,” a powerful, high-altitude ribbon of wind moving from west to east over the polar region, he said.
