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article imageGreenland ice sheet melting at alarming rate of speed

By Karen Graham     Dec 6, 2018 in Science
The Greenland ice sheet is melting faster today than at any point in the last 350 years, according to a new study. The study found that the rate of melting is "off the charts."
Glaciologist and climate scientist Luke Trusel of Rowan University, led a team of U.S. and European researchers who analyzed more than three centuries of melt patterns in ice cores from western Greenland. The team's findings were published in the journal Nature on December 5, 2018.
"Melting of the Greenland Ice Sheet has gone into overdrive. As a result, Greenland melt is adding to sea level more than any time during the last three and a half centuries, if not thousands of years," Trusel said in a press release from the Woods Hole Oceanographic Institution (WHOI), one of the institutions involved in the research.
Sarah Das, a glaciologist at Woods Hole Oceanographic Institution (WHOI) and co-author of the study notes that from a historical perspective, today's ice melt is "off the charts."
“We found a fifty percent increase in total ice sheet meltwater runoff versus the start of the industrial era, and a thirty percent increase since the 20th century alone," she said.
Rising sea levels
The study found that melting from the Greenland ice sheet began in the 1800s, around the time of the Industrial Revolution. The Arctic began to warm as humanity began to pump greenhouse gases (GHG) into the atmosphere.
Iceberg calving into the ocean from the edges of the glaciers is of course, one part of how fresh water re-enters the ocean, however, over "half of the ice sheet water entering the ocean comes from runoff from melted snow and glacial ice atop the ice sheet."
The study warns that if the ice sheet melting "continues at unprecedented rates," this could accelerate the already fast rate of sea level rise.
“Rather than increasing steadily as climate warms, Greenland will melt increasingly more and more for every degree of warming. The melting and sea level rise we’ve observed already will be dwarfed by what may be expected in the future as climate continues to warm,” said Trusel.
Runoff in Greenland over the last 20 years is 50 percent greater than pre-industrial  and 33 percent...
Runoff in Greenland over the last 20 years is 50 percent greater than pre-industrial, and 33 percent greater than the 20th century alone.
Like Trusel
Ice cores tell the story of Greenland's ice melt
To determine the intensity of Greenland's ice melt over the centuries, researchers used a drill bit the size of a traffic pole to extract ice cores from the ice sheet and an adjacent coastal ice cap, all of them at elevations 6,000 feet above sea level.
If anyone wonders why the cores were drilled at such a high elevation - it is because the cores would contain records of past melt intensity, dating back to the 17th century.
In the warmer summer months, melting occurs across much of Greenland's ice sheet surface. At lower elevations, melting is more intense. Mwltwater from the ice sheet runs off into the ocean, contributing to sea level rise. But no record of the melt at lower elevations remains.
But in contrast, at higher elevations, summer meltwater quickly refreezes from contact with the below-freezing snowpack it lies on - preventing the meltwater from running off. Instead, it forms distinct icy bands that stack up in layers of densely packed ice over time.
Ice core samples were brought back to the labs at the U.S. National Science Foundation Ice Core Facility in Denver, Colorado., WHOI in Woods Hole, Massachusetts, Wheaton College in Norton, Mass, and the Desert Research Institute in Reno, Nevada. At these facilities, the cores were examined.
Combining results of melting found in the ice cores with satellite observations and sophisticated climate models, the researchers were able to reconstruct meltwater runoff at the lower-elevation edges of the ice sheet—the areas that contribute to sea level rise.
"We have had a sense that there's been a great deal of melting in recent decades, but we previously had no basis for comparison with melt rates going further back in time," study author and MIT-WHOI graduate student Matt Osman said.
Calving front of Helheim Glacier in South East Greenland (May 2005) photographed during a NASA surve...
Calving front of Helheim Glacier in South East Greenland (May 2005) photographed during a NASA survey flight.
NASA/Wallops
"By sampling ice, we were able to extend the satellite data by a factor of 10 and get a clearer picture of just how extremely unusual melting has been in recent decades compared to the past."
The research has found that the Greenland ice sheet isn't melting at a steady rate. Instead, each degree of warming increases the amount of melting, meaning the more the planet warms, the more sensitive the ice sheet will be.
"We can't rule out that the IPCC (Intergovernmental Panel on Climate Change) sea level rise scenarios are too conservative," University of Lincoln climate scientist Edward Hanna, who was not involved in the study, said. "Greenland is a bit like a sleeping giant that is awakening. Who knows how it will respond to a couple of more degrees of warming? It could lose a lot of mass very quickly."
More about Greenland, Ice sheet, nonlinear, Climate change, Sea levels