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Low, thin clouds triggered record melting of Greenland

A new study finds the largest ice melt in Greenland – a country covered by a large ice sheet – that took place in summer 2012 may have been due to low, thin clouds.

The ice melt, which has captured the attention of climate scientists since 1979, is so extreme that records suggest melt rate is nearly unprecedented. Scientists say the current melt rate is unmatched over the course of the past 100 years, and that melt rates on this scale only occur once every 150 years. Furthermore, researchers estimate that if the melting continues at this rate and the entire ice sheet dissolves, it would destroy 720,000 cubic miles of ice, in turn elevating global sea levels by 24 feet.

“The July 2012 event was triggered by an influx of unusually warm air, but that was only one factor,” said study researcher Dave Turner, a physical scientist at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory. “We show that low-level clouds were instrumental in pushing temperatures up above freezing.”

Turner and his team were able to discern the role of clouds on the ice sheet melt after careful analysis of temperature data from the ICECAPS trial performed above at Summit Station – the location of the summer melt – approximately 10,500 feet above sea level.

Although low clouds are not known to play a role in ice melting – they usually reflect solar energy back into space and lower the overall temperature – results from computer climate models suggest that cloud widths are the perfect size to contribute to thawing. The clouds are thin enough to permit sunlight to pass through the cloud – heating the ice surface – but just thick enough to shut in any thermal radiation emitted upward by the warming surface.

According to Ralf Bennartz, lead author of the study and an atmospheric physicist at the University of Wisconsin at Madison, the findings suggest that clouds appear approximately 30-50 percent of the time over both Greenland and across the Arctic.

“A very narrow range of cloud thickness allows for amplification of surface warming,” said Bennartz. “This shows how well we have to understand individual components of the climate system, such as clouds, in order to accurately understand the system as a whole.”

However, he added that further observation is needed to better comprehend these components.

“We need to continue detailed observational studies at Summit Station in Greenland in order to better understand processes leading to melting of the Greenland Ice Sheet and help improve the representation of these processes in global climate models,” Bennartz said.

The study is the latest research to suggest that global climate change is likely a far more complicated problem than previously thought. A series of reports released earlier this year detailed findings that show the Arctic may become more temperate as temperatures rise, while another study showed ice melt in Antarctica could actually slow the effects of global warming.

A number of policy recommendations presented by policy makers around the world often cite the melting of the Greenland ice cap as a major threat to coastal regions. The ice cap, one of the largest in the world, could lead to rising seas, possibly causing millions of people to relocate.

The study is published in the April 4 issue of the journal Nature.

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