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%.
The NASA albedo data have an accuracy better than 5% (Stroeve et al. 2006; Box et al. 2012).
- Aerial oblique view of the lower elevations of the ice sheet in August 2005 from an area near the point of lowest reflectivity on the ice sheet. Photo J. Box
Impurities are composed of dust, algae, wildfire soot. Their relative importance to surface albedo remains incompletely understood.
As part of Dark Snow Project’s 2013 expedition, Dr. Marek Stibal gathers samples from an area of concentration near the darkest point on the Western Greenland ice sheet.
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.
Greenland albedo started out very low in 2013 due to a snow drought exposing darker bare ice around the ice sheet periphery.
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.
Light absorbing impurities like black carbon from wildfire and industrial sources acts like a multiplier of the albedo feedback.
The Dark Snow Project aims to better understand the black carbon aspect of the albedo feedback through field data gathering and laboratory analysis.
Click here to visit the Dark Snow Youtube Channel.
- Box, J. E., X. Fettweis, J.C. Stroeve, M. Tedesco, D.K. Hall, and K. Steffen: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012. open access
- Stroeve, J.C., Box, J.E., Haran, T., 2006: Evaluation of the MODIS (MOD10A1) daily snow albedo product over the Greenland ice sheet, Remote Sensing of Environment, 105(2), 155-171.
- Stibal, M. M. Šabacká, and J. Žárský, Biological processes on glacier and ice sheet surfaces, Nature Geoscience 5, 771–774, 2012, doi:10.1038/ngeo1611