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Tag:

ice sheet

Widespread Greenland Melting Due to Forest Fires and Warming, Study Says

Widespread Greenland Melting Due to Forest Fires and Warming, Study Says

written by Yale Environment 360

Rising temperatures and ash from Northern Hemisphere forest fires combined to cause large-scale surface melting of the Greenland ice sheet in 2012, an echo of a similar event that occurred in 1889, a new study finds.

The massive Greenland ice sheet — the second largest ice body in the world after the Antarctic ice sheet — experiences annual melting at low elevations near the coastline, but surface melt is rare in the dry snow region in its center. In July 2012, however, satellites observed for the first time surface melt across more than 97 percent of the ice sheet, generating reports that the event was almost exclusively the result of climate change.

greenland_ice_melt_nasa_july_2012These NASA maps show how, within the space of four days in the summer of 2012, Greenland’s vast ice sheet faced a degree of melting not seen in three decades of satellite observations. The image at left shows the ice sheet on July 8, 2012, with a large part of it experiencing no melting (shown in white) in summer, as is typical. By July 12, 2012, the surface of virtually the entire ice sheet was melting (shown in red). (Image credit: NASA)

In the new report, published in the journal Proceedings of the National Academy of Sciences, researchers analyzed an ice core from the dry snow region of the ice sheet. Their findings indicate that in both 2012 and 1889 exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires to darken the surface of the ice sheet to a critical albedo threshold, causing the large-scale melting events. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, large-scale melt events on the Greenland ice sheet may begin to occur almost annually by the end of century, the researchers say.



May 21, 2014 1 comment
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New Data on What Greenland Was Like Almost 3 Million Years Ago

New Data on What Greenland Was Like Almost 3 Million Years Ago

written by Environmental News Network

Glaciers and ice sheets are commonly thought to work like a belt sander. As they move over the land they scrape off everything — vegetation, soil and even the top layer of bedrock. So a team of university scientists and a NASA colleague were greatly surprised to discover an ancient tundra landscape preserved under the Greenland Ice Sheet, below two miles of ice.

“We found organic soil that has been frozen to the bottom of the ice sheet for 2.7 million years,” said University of Vermont geologist and lead author Paul Bierman. The finding provides strong evidence that the Greenland Ice Sheet has persisted much longer than previously known, enduring through many past periods of global warming.

Greenland is a place of great interest to scientists and policymakers because the future stability of its huge ice sheet — the size of Alaska — will have a fundamental influence on how fast and high global sea levels rise from human-caused climate change.

“The ancient soil under the Greenland ice sheet helps to unravel an important mystery surrounding climate change,” said Dylan Rood, a co-author on the new study, from the Scottish Universities Environmental Research Centre and the University of California, Santa Barbara. “How did big ice sheets melt and grow in response to changes in temperature?”

The new discovery indicates that even during the warmest periods since the ice sheet formed, the center of Greenland remained stable. “It’s likely that it did not fully melt at any time,” Bierman said. This allowed a tundra landscape to be locked away, unmodified, under ice through millions of years of global warming and cooling.

“Some ice sheet models project that the Greenland Ice Sheet completely melted during previous interglacial periods. These data suggest that did not happen,” said co-author Tom Neumann, a cryospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “We don’t know how much of the ice sheet remained — to estimate it, we’d have to study other ice cores in Greenland that have sediment in the bottom to see if ancient soil is preserved under those sites as well.”

The scientists tested seventeen samples of “dirty ice” — ice with sediment mixed in — from the bottommost 40 feet of the 10,019-foot GISP2 ice core extracted from Summit, Greenland, in 1993. From this sediment, Bierman and a team at the University of Vermont’s Cosmogenic Nuclide Laboratory extracted a rare form of the element beryllium, an isotope called beryllium-10. Formed by cosmic rays, it falls from the sky and sticks to rock and soil. The longer soil is exposed at Earth’s surface, the more beryllium-10 it accumulates. Measuring how much is in soil or a rock gives geologists a kind of exposure clock.

Photo shows a piece of the GISP2 ice core that the researchers analyzed for the isotope beryllium-10, showing silt and sand embedded in ice. Soon after this picture was taken, the ice was crushed in the University of Vermont clean lab and the sediment was isolated for analysis.

The researchers expected to only find soil eroded from glacier-scoured bedrock in the sediment at the bottom of the ice core. But the silt they did find had very high concentrations of beryllium-10 when the team measured it on a particle accelerator at Lawrence Livermore National Laboratory, in Livermore, Calif.

Article by Roger Greenway



April 21, 2014 0 comment
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Sea Level Rise May be Underestimated by Models

written by Walter Wang

Think sea levels will rise only a bit in response to an increase in global temperature of one degree? Think again!

A new study estimates that global sea levels will rise about 2.3 meters, or more than seven feet, over the next several thousand years for every degree (Celsius) the planet warms.

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July 16, 2013 0 comment
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Greenland Ice May Foretell Future Global Warming Results

written by Walter Wang

When global warming is discussed, many will try to predict how much the ice cap will melt and how much the seas will rise. There are many variables in this calculation. A new study by an international team of scientists analyzing ice cores from the Greenland ice sheet going back in time more than 100,000 years indicates the last interglacial period may be a good analog for where

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January 25, 2013 0 comment
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