"12 August 2005, 8 PM local time, I took this photo from a helicopter flying over the ice sheet surface at ~1500 feet altitude. This is how much darker the Greenland ablation area [the summer melting area] is than a fresh snow surface that blankets it in wintertime. Along much of the southwestern ice sheet at the lowest 1000 m in elevation, impurities concentrate near the surface and produce this dark surface. Not all of the ice sheet is this dark, only the lower ~1/3 of the elevation profile of the ice sheet is. However, as melting increases on the ice sheet, so does the area exposed that is this dark."
Eric Holthaus then published more of his photos on Slate.com: