Greenland glaciers cross point of no return, will continue to shrink even if global warming stops today: Study
The ice sheet has been losing ice more rapidly than it is being replenished
Melting ice sheets in Greenland have passed a point of no return, warn scientists. According to them, glaciers on the island have shrunk to such an extent that even if humans somehow manage to stop climate change in its tracks and global warming were to stop today, the ice sheet would continue shrinking. The findings imply 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.
Shrinking glaciers in Greenland are a problem for the entire planet. The ice that melts or breaks off from Greenland’s ice sheets ends up in the Atlantic Ocean and eventually, all of the world’s oceans. Ice from Greenland is a leading contributor to sea-level rise. According to experts, enough ice melted or broke off from the Greenland ice sheet last year to cause the oceans to rise by 2.2 millimeters in just two months.
In the current study, the researchers analyzed nearly 40 years of satellite data from Greenland. “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,” explains Michalea King, lead author of the report and a researcher at The Ohio State University’s Byrd Polar and Climate Research Center, US.
The research team also includes experts from University of California Irvine, US; Utrecht University, The Netherlands; and Delft University of Technology, The Netherlands. They examined monthly satellite data from more than 200 large glaciers draining into the ocean around Greenland. The observations reveal how much ice breaks off into icebergs or melts from the glaciers into the ocean. The analysis, published in the journal Communications Earth and Environment, also shows the amount of snowfall each year, that is, the way these glaciers get replenished.
The authors found that, throughout the 1980s and 1990s, snow gained through accumulation and ice melted or calved from glaciers were mostly in balance, keeping the ice sheet intact. Through those decades, the ice sheets generally lost about 450 gigatons (about 450 billion tons) of ice each year from flowing outlet glaciers, which was replaced with snowfall.
The amount of ice being lost each year started increasing steadily around 2000 and the glaciers were losing about 500 gigatons each year. Snowfall did not increase at the same time and over the last decade, the rate of ice loss from glaciers has stayed about the same, implying the ice sheet has been losing ice more rapidly than it’s being replenished, explains the team. Before 2000, the ice sheet would have about the same chance to gain or lose mass each year. In the current climate, the ice sheet will gain mass in only one out of every 100 years, they add. The findings also reveal that large glaciers across Greenland have retreated about 3 kilometers on average since 1985. “We compare decadal variability in discharge and calving front position and find that increased glacier discharge was due almost entirely to the retreat of glacier fronts, rather than inland ice sheet processes, with a remarkably consistent speedup of 4-5% per km of retreat across the ice sheet. We show that widespread retreat between 2000 and 2005 resulted in a step increase in discharge and a switch to a new dynamic state of sustained mass loss that would persist even under a decline in the surface melt,” the experts state.
The scientists explained that 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. This implies that despite efforts to slow climate change, ice lost from glaciers draining ice to the ocean would likely still exceed ice gained from snow accumulation, and the ice sheet would continue to shrink for some time, caution experts. “Glacier retreat has knocked the dynamics of the whole ice sheet 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,” writes co-author Ian Howat, professor of earth sciences and distinguished university scholar at Ohio State.
The researchers emphasize that predictions of future change will require improved understanding of the ice or ocean boundary and controls on glacier calving. “It’s always a positive thing to learn more about glacier environments because we can only improve our predictions for how rapidly things will change in the future. And that can only help us with adaptation and mitigation strategies. The more we know, the better we can prepare,” says King.