The white, reflective surface of Greenland's snowpack is getting darker and less reflective, all thanks to what the Christian Science Monitor calls "positive feedback loops"—the idea that a little bit of melting leads to more and faster melting. "We knew that these processes had been happening," says Columbia professor Marco Tedesco, lead author of a new study in the journal Cryosphere. "What’s new is the acceleration of the darkening, which started in 1996." In fact, parts of Greenland may actually be 10% darker—technically it is losing its "albedo," or reflectivity—by the end of the century, researchers predict. "It's a train running downhill, and the hill is getting steeper," Tedesco says.
So what happened in 1996? One likely culprit is the natural change in atmospheric circulation called the North Atlantic Oscillation, in which summer atmospheric conditions "favored more incoming solar radiation and warmer, moist air from the south," Tedesco writes in Columbia's Earth Institute. This melting brought impurities such as soot from previous melts to the surface, making it darker and, in turn, prone to melting even faster. And because individual ice grains tend to get larger when snow melts and refreezes, less light scatters across those larger surfaces and more is absorbed, reports Gizmodo. This effect appears strongest in the infrared range the human eye cannot see but was found in satellite images. When the atmospheric conditions naturally shifted back in 2013, the damage had already been done, with the ice sheet more vulnerable to melting. (Check out how old the soil is under some parts of Greenland's ice pack.)