Greenland Is Melting Faster Than Scientists First Thought
Scientists will be forced to redirect their attention when monitoring the melting Greenland ice sheet, according to new research published this week, which shows that instead of focusing solely on the glaciers being driven into the sea in the country’s southeast and northwest regions, they will also need to focus on surface melt in the country’s southwest, which is helping to melt the Greenland ice sheet faster than scientists previously thought.
Scientists monitoring sea level rise have often focused on Greenland’s southeast and northwest regions where the mammoth glaciers push towards the Atlantic Ocean and deposit iceberg-size chunks of ice. This was described as “a response to both oceanic and atmospheric forcings” and resulted, between 2000 to 2010, in ice loss being concentrated in the southeast and northwest margins of the ice sheet, “in large part due to the increasing discharge of marine-terminating outlet glaciers, emphasizing the importance of oceanic forcing.”
The increased speed of a glaciers track towards the ocean thus increases the amount of freshwater melting into the ocean, causing a combination of increased sea level rise and potentially modifying ocean currents.
However, a new study published this week in the Proceedings of the National Academy of Sciences has revealed that the largest sustained ice loss between early-2003 to mid-2013 came instead from Greenland’s northwest region — a region mostly absent of icebergs, raising the question of what was melting.
“Whatever this was, it couldn’t be explained by glaciers, because there aren’t many there,” said Michael Bevis, lead author of the paper, Ohio Eminent Scholar and a professor of geodynamics at The Ohio State University. “It had to be the surface mass—the ice was melting inland from the coastline.” Specifically, Bevis and his co-authors believe that global warming is causing the ice sheet to melt inland which results in massive freshwater rivers feeding into the ocean. “We knew we had one big problem with increasing rates of ice discharge by some large outlet glaciers,” he said. “But now we recognize a second serious problem: Increasingly, large amounts of ice mass are going to leave as meltwater, as rivers that flow into the sea.”
Thus, where before the focus was on the southeast and northwest regions of the Greenland ice sheet, the southwest of Greenland is expected to become a serious threat and be a major future contributor to sea level rise.
Further, as Bevis explains, the damage has already been done. “The only thing we can do is adapt and mitigate further global warming—it’s too late for there to be no effect,” he said. “This is going to cause additional sea level rise. We are watching the ice sheet hit a tipping point.”
Data for the new study was supplied by the Gravity Recovery and Climate Experiment, better known as GRACE, which consists of twin satellites that measure ice loss across Greenland. GRACE, which was a joint mission between NASA in the United States and Deutsche Forschungsanstalt für Luft und Raumfahrt (DLR) in Germany and which was concluded in October 2017, has already shown that, between 2002 and 2016, the Greenland ice sheet “shed approximately 280 gigatons of ice per year, causing global sea level to rise by 0.03 inches (0.8 millimeters) per year.”
Michael Bevis and his team used data from GRACE and from GPS stations scattered across Greenland’s coast to identify changes in ice mass which showed that, by 2012, ice was being lost at nearly four times the rate that prevailed in 2003 — a change which was focused in the southwest. This increased loss was being caused by the North Atlantic Oscillation — which brings warmer air to West Greenland, as well clearer skies resulting in more solar radiation — which itself was building on anthropogenic climate change to cause unprecedented levels of melting and ice runoff.
“These oscillations have been happening forever,” Bevis said. “So why only now are they causing this massive melt? It’s because the atmosphere is, at its baseline, warmer. The transient warming driven by the North Atlantic Oscillation was riding on top of more sustained, global warming.”
“What’s happening is sea surface temperature in the tropics is going up; shallow water gets warmer and the air gets warmer,” Bevis continued. “The water temperature fluctuations driven by an El Niño are riding this global ocean warming. Because of climate change, the base temperature is already close to the critical temperature at which coral bleaches, so an El Niño pushes the temperature over the critical threshold value. And in the case of Greenland, global warming has brought summertime temperatures in a significant portion of Greenland close to the melting point, and the North Atlantic Oscillation has provided the extra push that caused large areas of ice to melt.”
“We’re going to see faster and faster sea level rise for the foreseeable future,” he concluded. “Once you hit that tipping point, the only question is: How severe does it get?”
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