According to a new study by scientists at NOAA and the Universities of Wisconsin, Idaho and Colorado, clouds over the central Greenland Ice Sheet last July were “just right” for driving surface temperatures there above the melting point. Published in Nature, they found that thin, low-lying clouds allowed the sun’s energy to pass through and warm the surface of the ice, while at the same time trapping heat near the surface of the ice cap. As you may have read there was a record breaking ice melt in 2012.
The fact that we are seeing this kind of melting would make one think we would redouble efforts to assure that we have contininuity in data track these issues but the fact is that we are facing a critical gap in satellite data. If the warming/ice melt trend continues studies show we will continue to see loss of coastal areas, reduction in the human workforce, and changes in growing seasons. The ice melt in Greenland is just one sign of many that our global ice is deminishing. in 2000 iceberg B15 broke off the Ross ice shelf to become the largest iceberg in recorde history. I only recently finished breaking up after floating since it broke off for 12 years.
“Thicker cloud conditions would not have led to the same amount of surface warming,” said Matthew Shupe, research meteorologist with NOAA’s Cooperative Institute for Research in Environmental Sciences at the University of Colorado and the NOAA Earth System Research Laboratory. “To understand the region’s future, you’ll need to understand its clouds. Our finding has implications for the fate of ice throughout the Arctic.”
In July, more than 97 percent of the Greenland Ice Sheet surface experienced some degree of melting, including at the National Science Foundation’s Summit Station, high atop the ice sheet. According to ice core records, the last time the surface at Summit experienced any degree of melting was in 1889, but it is not known whether this extended across the entire ice sheet.
“The July 2012 ice melt was triggered by an influx of unusually warm air sweeping in from North America, but that was only one factor,” said David Turner, research meteorologist with the NOAA National Severe Storms Laboratory and one of the lead investigators. “In our paper, we show that low-lying clouds containing a low amount of condensed water were instrumental in pushing surface air temperatures up above freezing and causing the surface ice to melt.”
Clouds can cool the surface by reflecting solar energy back into space, and can warm it by radiating heat energy back down to the surface. The balance of those two processes depends on many factors, including wind speed, turbulence, humidity and cloud “thickness,” or liquid water content.
In certain conditions, these clouds can be thin enough to allow some solar radiation to pass through, while still “trapping” infrared radiation at ground level. That is exactly what happened last July: the clouds were just right for maximum surface warming. Thicker clouds would have reflected away more solar radiation; thinner ones couldn’t have trapped as much heat, and in either of those cases, there would have been less surface warming.
“Our results may help to explain some of the difficulties that current global climate models have in simulating the Arctic surface energy budget, including the contributions of clouds,” said Ralf Bennartz, lead author for the study and professor at the University of Wisconsin-Madison. “Above all, this study highlights the importance of continuous and detailed ground-based observations over the Greenland Ice Sheet and elsewhere. Only such detailed observations will lead to a better understanding of the processes that drive Arctic climate.”