Greenland – an albedo feedback laboratory

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.

Snow and ice impurities concentrate in “cryoconite” holes on the Greenland ice sheet surface. Photo. J. Box

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).

During melting, the rounding of ice crystals by heating causes the albedo to drop.
A freshly fallen snow crystal has numerous facets to reflect sunlight (left). Warming causes the grains to round at the edges and clump together (right). Scanning electron microscope photos courtesy the Electron and Confocal Microscopy Laboratory, USDA Agricultural Research Service.
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%.
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.

Works Cited

  1. 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
  2. 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.
  3. 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

2 Responses to “Greenland – an albedo feedback laboratory”

  1. More Science and Visuals from Greenland | Climate Denial Crock of the Week Says:

    [...] Meltfactor: Jason Box’s blog: 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. [...]

  2. Doug Bostrom Says:

    A post densely packed with information as usual. Thank you!

    SEM images of melting snowflake are spectacular, a treat.

    On a semi-related note, has anybody produced an estimate of how many joules of energy are being transported into the interior of the GIS via meltwater? Presumably meltwater hovers around freezing point so that number seems easy to obtain but what’s the total mass of liquid water being absorbed each year?

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