More Science and Visuals from Greenland
July 1, 2013
Extreme contrasts between warm, moist air, and cold dry air, make for rapid and dramatic change in the environment of coastal Greenland, as evidenced in this mysterious fog effect over Sisimiut.
Surface reflectivity of sunlight is called “albedo”. Albedo is a Latin-based word referring to whiteness. The higher the albedo, the more sunlight can be reflected. As albedo decreases, more sunlight can be absorbed.
The absorption of sunlight is the largest single source of melt energy on the Greenland ice sheet.
Surface albedo across Greenland is mapped using data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) satellite-borne sensors. Before melting is underway, albedo is above 80%.
During melting, the rounding of ice crystals by heating causes the albedo to drop.
In some areas of the ice sheet, by the time winter snow cover melt away, bare glacier ice is exposed. Where impurities congregate, the surface albedo drops below 30%.
Impurities are composed of dust, algae, wildfire soot. Their relative importance to surface albedo remains incompletely understood.
An increase in atmospheric heating of Greenland ice is a driver of Greenland ice albedo decline in summer, in part due to the expansion of bare ice areas, in part due to the heating effect on rounding ice crystals, and in part if the concentration of impurities increases.
In the period of high quality observations beginning early 2000, June 2013 albedo for the ice sheet is ranked 3rd lowest.
The albedo feedback with climate is responsible for doubling the temperature changes when climate warms or cools. This amplifier helps Earth’s climate system swing into and out of ice ages. The feedback is complex, including the effects of heating and light absorbing impurities, in a process that compounds through time.