Clouds over the central Greenland Ice Sheet last July were âjust rightâ for driving surface temperatures there above the melting point, according to a new study by scientists at the National Oceanic and Atmospheric Administration and the universities of Wisconsin, Idaho and Colorado. The study, published April 3, 2013 in Nature, found that thin, low-lying clouds allowed the sunâs 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. This combination played a significant role in last summer's record-breaking melt.