Messages From Greenland Ice

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Surface meltwater ponds in Western Greenland in May 2019. NASA/JEFFERSON BECK

For his third appearance in our pages this year, illuminating a topic we all need to understand more fully, thanks to Jon Gertner for sharing this in Yale e360:

In Greenland’s Melting Ice, A Warning on Hard Climate Choices

Greenland is melting at an unprecedented rate, causing vast quantities of ice to disappear and global sea levels to rise. The fate of the ice sheet is not sealed, but unless CO2 emissions are sharply cut, the long-term existence of Greenland’s ice is in doubt.

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A team from the Danish Meteorological Institute travels by dogsled across a pond of meltwater in northwest Greenland to retrieve equipment on June 13. STEFFEN M OLSEN/TWITTER

The heat wave arrived early this spring — a shroud of temperate air, sweeping in during early June, which enveloped the Northern Hemisphere’s biggest ice sheet in a stifling hug. At its peak, nearly 45 percent of Greenland’s frozen surface turned to meltwater, coloring the huge white expanse with sapphire lakes and lapis streams. During the warmest stretch, runoff from the ice sheet amounted to about 2 billion tons, which meant that at the same time Greenland was losing water, the North Atlantic was gaining it. Some areas on the island were 40 degrees Fahrenheit above normal for this time of year.

“We didn’t see anything like this prior to the late 1990s,” Thomas Mote, a University of Georgia scientist who monitors summer melting on the ice sheet, explained to CNN. “The melting is big and early,” Jason Box, a climatologist with the geological survey of Denmark and Greenland, informed the Washington Post.

Greenland’s ice sheet covers about 80 percent of the island, and measures about 660,000 square miles; in its center, it runs to a depth of about two miles. According to the most recent NASA studies, the ice sheet holds enough water to raise sea levels by about 24 feet, should it ever disappear completely.

It’s worth noting that the ice has undergone summertime melting events ever since visitors to the island have made field observations. Hinrich Rink, the first Danish researcher to seriously investigate the contours of Greenland’s ice, correctly surmised that it was the last remaining link to ice sheets that had covered Northern Europe and northern North America during previous ice ages — a “Rosetta Stone” that could explain the mysteries of a lost, frozen world. During one summer trip in the mid-1800s, Rink surveyed the western edge of Greenland’s ice and described rushing streams that cut through the ice and dropped into depthless moulins. Where did Greenland’s meltwater go, Rink wondered?

Yet we now know that the Greenland of today is different from the Greenland that Rink experienced. The ice sheet is melting more, and melting earlier in summer, and melting in ways that computer models suggest will ultimately threaten its long-term existence. A recent paper in Nature presented compelling evidence, gathered from cores extracted from the ice sheet, that demonstrated Greenland’s recent melt is “exceptional” over the past 350 years and that the ice sheet’s response to higher temperatures is now “nonlinear.” In the last two decades, melting rates of the ice are 33 percent higher than 20th century averages; the melting, moreover, is not only increasing but accelerating.

Many scientists who have spent their careers on the ice sheet have witnessed these changes firsthand. Konrad Steffen, who has built up a record of meteorological readings around Greenland over the course of the past 30 years, has calculated that between 1990 and 2018 average temperatures on the ice sheet have increased by about 2.8 degrees Celsius, or 5 degrees Fahrenheit. While the highest points on the ice sheet are still mostly resistant to melting, over the same 30-year time period the total area of the ice sheet that has become vulnerable to surface melting has increased by around 65 percent. And what seems clear now is that Greenland is no longer changing in geological time. It is changing in human time…

Read the whole article here.

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