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Arctic Albedo

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Arctic Albedo

by Steven Goddard

Looking at the June 14 satellite photo above, you see the view which the Sun sees of the North Pole.

Well not exactly, because the elevation of the Sun at its peak (mid-June) is actually fairly low in the sky. At the Pole, it is only 23.5º above the horizon. The video below shows what the earth would look like now, viewed from perpendicular to the plane of the ecliptic. Note that the region north of 66.5º is in perpetual light. The image of the Sun is from the days when it used to have sunspots.

Now, looking at the satellite photo again, we see three different shades of white. Snow is the brightest white (highest albedo) and can be seen in Greenland. Clouds are next brightest white, and at least partially cover almost the entire Arctic. In a few locations, you can see dirty white sea ice peeking out through the clouds.

We often hear that sea ice controls Arctic albedo. There is some truth to this statement, but the real story is that the albedo of clouds actually controls the area of sea ice. When it is cloudy, little melting occurs. When it is sunny, the ice is more prone to melt.

Consider this chart from the University of Alaska.

They forecast the breakup of sea ice based on the total amount of sunshine received. When accumulated sunshine reaches 700 MJ/m², the ice breaks up. In a cloudy year (like 2009) this occurs later. In a sunny year (like 2007) it occurs earlier. 2010 is right in the middle. On a cloudy day, most of the sunshine reflects back into space from the top of the white clouds. That is why we see the bright white clouds in the satellite image.

The real key to Arctic albedo, and melt – is clouds. Can climate models effectively forecast cloudiness? Short answer – no. Clouds are one of the Achilles Heels of climate models. So next time you hear about a climate model forecasting an ice free Arctic, ask if they have the cloud problem under control.

It is cloudy at Santa's Workshop right now.

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