Greenland's ice sheet melt rate unprecedented, happening faster than anybody thought

Sarah Das  WHOI		Large rivers form on the surface of the ice sheet in summer rapidly moving meltwater from the ice sheet to the ocean

Sarah Das WHOI Large rivers form on the surface of the ice sheet in summer rapidly moving meltwater from the ice sheet to the ocean

They showed that melting of Greenland's surface ice began increasing in the mid-19th century and then ramped up dramatically during the 20th and early 21st centuries.

A team of scientists journeyed to Greenland in 2015 to observe and measure the rate that the colossal ice sheets in the region are melting.

Greenland's ice sheet is now melting at a rate that is "off the charts" compared with the last 350 years, a new study by scientists from Woods Hole Oceanographic Institution (WHOI) has warned.

"From a historical perspective, today's melt rates are off the charts, and this study provides the evidence to prove this", said Dr. Sarah Das, a glaciologist at WHOI and co-author of the study. "We found a 50 percent increase in total ice sheet meltwater runoff versus the start of the industrial era, and a 30 percent increase since the 20th century alone".

The study confirms ice loss from Greenland is one of the main factors contributing to the sea level rise.

Melting Greenland ice sheets may raise sea levels as much as an eye-popping seven meters (23 feet), endangering coastal cities like New York, Lagos, and Shanghai, according to a new study. This means that the sea level could rise sooner and faster than previously assumed.

While the researchers were able to demonstrate their ice core melt record was generally applicable across of Greenland by correlating recent history with satellite records and model predictions, the southeastern margin is one area where an independent core would help verify trends. The scientists drilled at these elevations to ensure the cores would contain records of past melt intensity as far back as the 17th century. "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". 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.

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While huge chunks of ice popping off Greenland's margins get more attention, the steady runoff of water from its surface is now the largest contributor to Greenland's rapid slim-down. Instead of escaping the ice sheet, the short-lived meltwater forms icy bands that stack up layers of densely packed ice over time.

Researchers from the MIT-WHO Joint Program, University of Washington, Wheaton College, University of Leige, Desert Research Institute, and Utrecht University also worked on the study.

The long-term record the researchers built from these layered ice cores allowed them to spot a slight trend of increased melting across Greenland coinciding with the beginning of modern-day warming in the mid-1800s. Mwltwater from the ice sheet runs off into the ocean, contributing to sea level rise.

"The melting is not just increasing - it's accelerating", Trusel told Nature.

Trusel said the new research provides evidence that the rapid melting observed in recent decades is highly unusual when put into a historical context.

The authors also note that Greenland's ice sheet is much more vulnerable to melting than before.

"Even a very small change in temperature caused an exponential increase in melting in recent years", she said. "Anything we can do to limit future warming, even by a little bit, is going to make a huge difference to keeping ice on Greenland and not in the ocean".

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