arctic sea without ice in7 years

This is of course a lurid title, a striking statement, which no responsible scientist would make, because it lacks some explanation.

I am going to give it herewith.

Strictly, the sentence should go like this:

If one extrapolates into the future the trend visible in the arctic ice volume data compiled since 1979, one comes to the conclusion, that the arctic sea will very probably be completely ice-free for the first time in september, the month of smallest ice volume, between 2015 and 2020.

After that, it it will possibly show some year ice cover in september but only for a short period of time.

The point of total ice-freeness lies  – extrapolating the present trend – somewhere around 2035, a datum, which has as things are a pretty high uncertainty on it.

To come to that I interpreted the data of the Polar Science Center of Washington University by calculating the somewhat enigmatic plot here back into absolute ice volume values:


The seasonal changes are beautifully depicted and also the decrease of the mean value. If one continues the lower touching line by finger, one gets to region around 2017. You won’t get a more reliable value with mathematical methods. Crucial is whether you take the slight but clearly perceptible bending downward into account or not. In the latter case, you would land on the zero line 10 years later.

If you continue the upper touching line, you get to the above mentioned 2035, but of course in this longer time span the process may as well accelerate as slow down.

What does this mean?

Ice has a higher coefficient of reflection than water. Hence in polar summer, more sunlight will be absorbed. On the other hand ice emits during night and winter less thermal radiation into space than water. Both statements are valid only without the sky being cloud covered. So it is not a priori clear, whether the energy balance over the year of the ice-freeness is positive or negative. Anyway it will depend very much on the cloud cover pattern.

What is clear, is that the weather system of the northern hemisphere will change, because the air over the arctic region will no longer be cooled as much as hitherto.


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August 2010
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