Greenland Something Less than Snow White

July 3, 2012

12 August 2005, 8 PM local time, Photo from a helicopter flying over the ice sheet surface at ~1500 feet altitude. This is how much darker the Greenland ablation 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.

Meltfactor is the blog of Jason Box, of the Byrd Polar Center at Ohio State U.

Meltfactor:

The following provides detail to a story run by NOAA entitled Greenland Ice Sheet Getting Darker

Freshly fallen snow under clear skies reflects 84% (albedo= 0.84) of the sunlight falling on it (Konzelmann and Ohmura, 1995). This reflectivity progressively reduces during the sunlit (warm) season as a consequence of ice grain growth, resulting in a self-amplifying albedo decrease, a positive feedback. Another amplifier; the complete melting of the winter snow accumulation on glaciers, sea ice, and the low elevations of ice sheets exposes darker underlying solid ice. The albedo of low-impurity snow-free glacier ice is in the range of 30% to 60% (Cuffey and Paterson, 2010). Where wind-blown-in and microbiological impurities accumulate near the glacier ice surface (Bøggild et al. 2010), the ice sheet albedo may be extremely low (20%) (Cuffey and Paterson, 2010). Thus, summer albedo variability exceeds 50% over parts of the ice sheet where a snow layer ablates by mid-summer, exposing an impurity-rich ice surface (Wientjes and Oerlemans, 2010), resulting in absorbed sunlight being the largest source of energy for melting during summer and explaining most of the inter-annual variability in melt totals (van den Broeke et al. 2008, 2011).

The photo below shows how dark the ice sheet surface can become in the lowest ~1000 m elevation in the “ablation area” after the winter snow melts away and leaves behind an impurity-rich surface. This dark area is where the albedo feedback with melting is strongest.

Dirty ice surrounds a meltwater stream near the margin of the ice sheet. Compared to fresh snow and clean ice, the dark surface absorbs more sunlight, accelerating melting. © Henrik Egede Lassen/Alpha Film, from the Snow, Water, Ice, and Permafrost in the Arctic report from the U.N. Arctic Monitoring and Assessment Programme.

Satellite observations from the NASA Moderate-Resolution Imaging Spectroradiometer (MODIS)  indicate a significant Greenland ice sheet albedo decline (-5.6±0.7%) in the June-August period over the 12 melt seasons spanning 2000-2011. According to linear regression, the ablation area albedo declined from 71.5% in 2000 to 63.2% in 2011 (time correlation = -0.805, 1-p=0.999). The change (-8.3%) is more than two times the absolute albedo RMS error (3.1%). Over the accumulation area, the highly linear (time correlation = -0.927, 1-p>0.999) decline from 81.7% to 76.6% over the same period also exceeds the absolute albedo RMS error.

Greenland ice sheet average reflectivity or albedo (multiply by 100 to get % units) for 12 summer (June-August) periods.

NOAA Climate Watch:

According to Jason Box, the lead author of the Greenland chapter of the 2011 Arctic Report Card and the analyst of the reflectiveness data, the darkening in the interior is just as remarkable than the changes at the margins. The interior is the high-point of the dome-shaped ice sheet, rising to nearly two miles above sea level. There is no visible melting there in the summer, so why is the area becoming darker?

Map of changes in the percent of light reflected by the Greenland Ice Sheet in summer (June-July-August) 2011 compared to the average from 2000-2006. Virtually the entire surface has grown darker due to surface melting, dust and soot on the surface, and temperature-driven changes in the size and shape of snow grains. Map by NOAA’s climate.gov team, based on NASA satellite data processed by Jason Box, Byrd Polar Research Center, the Ohio State University.

The darkening in the non-melting areas, says Dr. Box, is due to changes in the shape and size of the ice crystals in the snowpack as its temperature rises. Snow grains clump together, and they reflect less light than the many-faceted, smaller crystals. Additional heat rounds the sharp edges of the crystals. Round particles absorb more sunlight than jagged ones do.

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.

About these ads

10 Responses to “Greenland Something Less than Snow White”


  1. [...] Meltfactor is the blog of Jason Box, of the Byrd Polar Center at Ohio State U. Meltfactor: The following provides detail to a story run by NOAA entitled Greenland Ice Sheet Getting Darker… Fresh…  [...]

  2. villabolo Says:

    It’s getting darker by the minute.

    Of course, any models as to how fast Greenland will melt is likely to be a gross underestimate. How long will it take to get a disastrous 1′ increase in sea level? It’s not merely the flooding but it augmentation of Hurricane flood damage – a mere Category 3 would be nasty with such higher waters.

    • MorinMoss Says:

      Thx 4 link. I’m also looking at other years. I know many are saying it’s too early to make the call but there would have to be a drastic weather change in the Arctic for this not to be a serious contender for lowest extent.

      The sea ice concentrations, which I rarely see as a main article at Denier Central, are quite low for this time of year.

      BTW, where is all the 2009 data?

  3. otter17 Says:

    Wow, a decline of several percentage points in albedo within a decade?

  4. jdouglashuahin Says:

    It may not be the best time of the summer to plant the banana trees on Greenland.
    Summit, Greenland
    5:18 AM WGST on July 05, 2012 (GMT -0200)
    Elev: 3207 m
    Lon: 38.5° W
    Lat: 72.6° N

    -9 °C
    Mostly Cloudy

    Tonight
    -17 °C
    Chance of Snow
    40% chance of precipitation

    http://www.wunderground.com/cgi-bin/findweather/getForecast?query=72.58000183,-38.45000076

    • otter17 Says:

      No kidding. What is your point? Oh, I get it. You are attempting to make a poor argument based on a fallacy of scale.

      Article says:
      “Greenland albedo is decreasing fast, providing an additional feedback for melting of the ice sheet along with increasing temperatures.”

      You say:
      “Well, the temperature increase can’t be THAT much since you can’t grow banana trees there yet.”

      When a scientist says something based on evidence and direct observations, try listening, rather than attempting to come up with some lame attempt to refute him/her.

      Look we get that you hate all the solutions for climate change. Be an adult and come up with a solution that works for your ideals. Stop trying to shoot the messengers (scientists).

      • greenman3610 Says:

        You can’t grow bananas in Greenland. Therefore, the radiative properties of greenhouse gases are refuted.
        Physics for Deniers.


Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 1,639 other followers

%d bloggers like this: