The Earth Observatory newsletter yesterday had several great stories and photos. Here are some photos, excerpts and links to the one on Greenland's dark ice:
In the past, the bright surface of the Greenland Ice Sheet reflected well over half of the sunlight that fell on it. This reflectiveness helped keep the ice sheet stable, as less absorbed sunlight meant less heating and melting. In the past decade, however, satellites have observed a decrease in Greenland’s reflectiveness. This darker surface now absorbs more sunlight, which accelerates melting.
The map above shows the difference between the amount of sunlight Greenland reflected in the summer of 2011 versus the average percent it reflected between 2000 to 2006. Virtually the entire ice sheet shows some change, with some areas reflecting close to 20 percent less light than a decade ago. The map is based on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on NASA’s Terra and Aqua satellites. It was produced as part of the National Oceanic and Atmospheric Administration’s Arctic Report Card.

Ohio State University scientist Jason Box says the darkening is due to changes in the shape and size of the ice crystals in the snowpack. The grains of snow clump together and reflect less light than the many-faceted, smaller crystals. Sharp crystal edges become rounded when exposed to more heat. These absorb more sunlight than jagged snow crystals:

Read mora via earthobservatory.nasa.gov