The Greenland ice sheet is melting faster than forecast

Eloise Marshall
December 7, 2018

To study the melting of Greenland's ice sheet, the team used a large drill to collect ice cores from sites more than 6,000 feet above sea level on the ice sheet and a nearby ice cap.

Melting ice in Greenland, home to the second largest mass of ice after Antarctica, is thought to add 0.8 millimetres of water to global ocean levels annually, more than any other region, according to NASA. Across the ice sheet, melting was more rapid in 2012 than any other year and the most recent decade included in the ice core-analysis, 2004-2013, experienced "a more sustained and greater magnitude of melt than any other 10-year period" in the 350-year record, the scientists wrote. Data suggests that even small changes in temperature caused exponential increases in melting in recent years - a non-linear response that points to feedback effects. At such locations, meltwater runs off the ice sheet and into the ocean, contributing to sea level rise - but in the process, no record of the melt remains.

Low-lying tropical island states from the Maldives to Tuvalu view Greenland's ice sheet with foreboding since it contains enough ice to raise world sea levels by around 7 metres if it all melted. "We demonstrate that Greenland ice is more sensitive to warming today than in the past - it responds non-linearly due to positive feedbacks inherent to the system".

Meltwater slides off Greenland's massive ice sheet into the ocean during hot summer days.

"From a historical perspective, today's melt rates are off the charts and this study provides the evidence to prove it", said Sarah Das, a glaciologist at Woods Hole Oceanographic Institution in MA and co-author of the study.

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The research also discovers that the estimate of melting at Greenland's surface has shot up in recent years and now is beyond the limits of what was contemplated organic changeability over the last few centuries. The researchers found that the rate translated to a 50-percent increase in the runoff of meltwater into the sea compared with the preindustrial era. This frozen meltwater creates distinct ice bands that pile up over years to form layers of densely packed ice. This gave a record of past melt intensity going back to the 17th century.

Combining results from multiple ice cores with observations of melting from satellites and sophisticated climate models, the scientists found the thickness of the annual melt layers they observed clearly tracked not only how much melting was occurring at the coring sites, but also much more broadly across Greenland.

"We need to be aiming for net-zero emissions before 2050".

In the wake of October's dire report from the UN Intergovernmental Panel on Climate Change warning that civilization has just more than a decade to stave off climate catastrophe, Thursday's report spells more bad news for the planet, especially the millions of people living near the world's oceans.

Additional co-authors are: Matthew J. Evans, Wheaton College; Ben E. Smith, University of Washington; Xavier Fettweis, University of Leige; Joseph R. McConnell, Desert Research Institute; and Brice P.Y. Noël and and Michiel R. van den Broeke Utrecht University.

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