The Greenland Ice Sheet (GrIS) has been losing mass for several decades due to increased surface meltwater runoff and ablation of marine-terminating outlet glaciers via calving and submarine melting ice discharge. The Greenland Ice Sheet is losing mass at accelerated rates, making it the largest single contributor to rising sea levels.
The study by Ohio State University‘s Byrd Polar and Climate Research Center suggests that glaciers on the island have shrunk so much that even if global warming were to stop today, the ice sheet would continue shrinking.
Scientists looked at 40 years of satellite data from Greenland show how much ice breaks off into icebergs or melts from the glaciers into the ocean. They also show the amount of snowfall each year—the way these glaciers get replenished.
It implies that Greenland’s glaciers have passed a tipping point of sorts, where the snowfall that replenishes the ice sheet each year cannot keep up with the ice that is flowing into the ocean from glaciers.
All through the 1980s and 90s, snow gained through accumulation and ice melted or calved from glaciers were generally in balance, keeping the ice sheet intact. As the decades progressed, the scientists found that the ice sheets commonly lost around 450 gigatons of ice every year from flowing outlet glaciers replaced with snowfall.
Michalea King, a lead author of the study and a researcher at The Ohio State University’s Byrd Polar and Climate Research Center, said, “We’ve been looking at these remote sensing observations to study how ice discharge and accumulation have varied. And what we’ve found is that the ice that’s discharging into the ocean is far surpassing the snow that’s accumulating on the surface of the ice sheet.”
The amount of ice being lost each year—started increasing steadily around 2000, so that the glaciers were losing about 500 gigatons each year. Snowfall did not increase simultaneously, and over the last decade, the rate of ice loss from glaciers has stayed about the same. It means the ice sheet has been losing ice more rapidly than it’s being replenished. Before 2000, the ice sheet would have about the same chance to gain or lose mass each year. The ice sheet will gain mass in only one out of every 100 years in the current climate.
King said, “The glaciers have shrunk back enough that many of them are sitting in deeper water, meaning more ice is in contact with water. Warm ocean water melts glacier ice, and also makes it difficult for the glaciers to grow back to their previous positions.”
Ian Howat, a co-author on the paper, professor of earth sciences, and distinguished university scholar at Ohio State said, “Glacier retreat has knocked the whole ice sheet’s dynamics into a constant state of loss. Even if the climate were to stay the same or even get a little colder, the ice sheet would still be losing mass.”
“When all of these glaciers retreated at once, it was enough to significantly increase the rate at which ice flows into the ocean. It is like the spillway on the dam being opened up.”
According to lead author King, an extra 60 gigatonnes each year of snowfall or reduced melting for the glacier would be needed to return to a balanced state.
- King, M.D., Howat, I.M., Candela, S.G. et al. Dynamic ice loss from the Greenland Ice Sheet driven by sustained glacier retreat. Commun Earth Environ 1, 1 (2020). DOI: 10.1038/s43247-020-0001-2