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article imageThinning summer cloud cover responsible for Greenland ice melt

By Karen Graham     Jul 2, 2017 in Environment
Greenland's loss of ice has been the big story in climate-related news lately, and with good reason - a warming climate is responsible. And now we are beginning to understand why this is happening at such an accelerated rate.
British and Belgian scientists think have found one reason for the accelerated rate of ice melt in Greenland, and they have published their findings in the online journal, Science Advances.
The research, led by the University of Bristol, found that over the past two decades, there has been a marked decrease in the summer cloud cover over Greenland. This has allowed more solar radiation to warm the glaciers and ice pack. The study says that while the increased rate of melting has been attributed to "rising temperatures and a decrease in surface albedo," they found that the "abrupt reduction in surface mass balance since about 1995 can be attributed largely to a coincident trend of decreasing summer cloud cover enhancing the melt-albedo feedback."
The researchers used satellite imagery data and climate modeling to reach their conclusion that showed that just a one percent reduction in cloud cover resulted in an extra 27 billion metric tons of melting ice on Greenland's surface. To put that amount in perspective, that is equivalent to about the annual domestic water supply of the United States.
Aerial view of melting Greenland
Photo by Stig Nygaard
The different explanations for Greenland's ice loss
In September 2016, Digital Journal reported that scientists from the Danish Meteorological Institute (DMI) had found that 12 percent of the ice sheet was melting almost one month earlier than the previous top three dates for when more than 10 percent of the ice had begun to melt. The researchers attributed the melting to warming temperatures.
Then, in May, Digital Journal reported on a detailed study of the Rink Glacier and its loss of about 11 billion tons of ice each year since the early 2000s. The scientists blamed the increased ice loss on the effects of a "solitary waves" rippling through the glacier that were so strong, they reshaped the bedrock upon which the ice sheet sits.
Rink Glacier from 34 000 feet.
Rink Glacier from 34,000 feet.
John Sonntag-NASA/JPL
It was this study that also cited the soot from Siberian wildfires in 2012 that had coated the ice fields, resulting in 95 percent of the ice sheet going into meltdown.The study concluded that "the more warming, the more surface meltwater available to trigger ‘extraordinarily’ dynamic behavior of the glacier such as the one we discovered in Rink Glacier.”
And while these studies have shown to be significant in explaining some of what's happening to Greenland's glaciers and ice cover, the clouds that shield the Arctic region from solar radiation were not given the credit they are due. Since 1995, Greenland has lost 4,000 billion tons of ice, and “the impact of increased sunshine during summer is large, it explains about two-thirds of Greenland’s melting signal in recent decades,” said Stefan Hofer, a doctoral student at the University of Bristol, UK, who led the study.
Cloud circulation and the North Atlantic Oscillation
However, there is more to the explanation than just a decrease in summer cloud cover. Cloud cover can be dependent on the circulation of the air currents in the atmosphere. The researchers write, "We are seeing changes in the large-scale circulation patterns, which leads to more frequent sunshine and higher amounts of solar energy reaching the surface of the ice sheet”
Jet stream.
Jet stream.
And the scientists also found that one percent per year decrease in cloud cover between 1995 and 2009 could also be connected to a meteorological phenomenon called the North Atlantic Oscillation, a natural cycle that four years ago was linked to dramatic melting in Greenland.
Jonathan Bamber, a geographer at the University of Bristol points out that data shows there have been large-scale changes in the circulation pattern, all leading to more frequent and higher amounts of solar energy reaching the Greenland ice sheet. “This highly unusual state of the atmosphere has been linked to record low sea ice cover during summer over the Arctic Ocean. This highlights the coupled nature of the climate system and the consequences of changes in one component on another.”
More about melting ice, cloud cover, Greenland, Summer, North Atlantic Oscillation