Thin, Low Clouds Reason behind Drastic Greenland Ice-Melt of 2012
According to a new study, the record-breaking melting of the Greenland Ice Sheet was due to uncommon weather and low, thin clouds.
The data for the study came from an experiment called as ICECAPS (Integrated Characterization of Energy, Clouds, Atmospheric state, and Precipitation at Summit).
Although ice-melts have been documented since the 1970s, the ice-melt of 2012 was a rare event, estimated to occur just once in every 150 years or so.
"In July 2012 a historically rare period of extended surface melting raised questions about the frequency and extent of such events. Of course, there is more than one cause for such wide-spread change. We focused our study on certain kinds of low-level clouds," said Ralf Bennartz, from the Department of Atmospheric and Oceanic Sciences and scientist with the Space Science and Engineering Center at the University of Wisconsin-Madison.
One of the factors that triggered the ice-melt was the "an influx of unusually warm air," said Dave Turner of NOAA-NSSL, one of the lead investigators. "In our paper we show that low-level clouds were instrumental in pushing temperatures up above freezing," he added.
Low-level clouds radiate infrared energy to the surface. A set of complex conditions affect ice-melt, like wind speed, temperature and humidity, heat transfer between the snow layers, etc.
When the clouds near the ground become thin, they start radiating the sun's rays to the ground instead of reflecting it. These rays, along with the already trapped infrared radiation, are enough to increase the temperature above freezing point.
The extent to which these thin low-lying clouds affect the ice-melt wasn't known to researchers earlier.
"We know that these thin, low-level clouds occur frequently. Our results may help to explain some of the difficulties that current global climate models have in simulating the Arctic surface energy budget. Above all, this study highlights the importance of continuous and detailed ground-based observations over the GIS and elsewhere. Only such detailed observations will lead to a better understanding of the processes that drive Arctic climate," said Bennartz in a news release.
The Greenland Ice Sheet is about 1,500 miles long and 680 miles wide, which makes it the second largest ice sheet in the world. If all this ice were to melt entirely in a day, global sea-levels would rise by 24 feet, according to the Space Science and Engineering Center, University of Wisconsin-Madison.
The study is published in the journal Nature.