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gnumb
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Most or all of the commenters here know much more about ice and climate than I do, so I try to keep my mouth shut, but. I'm not sure why Al Rodger says we shouldn't examine Wadhams' calculation. As pointed out by Al Rodger at 18:27 Sphaerica at 18:18, Thereoncewasawindmill at 15:10, and Peter Ellis at 15:53, his calculation is "far too simplistic", due to 1. basic geometry 2. the way the reflectivity of water varies with angle of incident light 3. clouds 4. probably many other complicating feedbacks I haven't thought of. The geometry is exactly the same geometry that makes the Arctic colder than the tropics: on average over a year, the Earth's surface in the Arctic is much more oblique to the Sun's rays, so less light reaches the surface in the Arctic. The "present summer area of sea ice" may be 4/510 of the Earth's area, but the light falling on that ice is less than 4/510 of the total light falling on the Earth. A change in the albedo of the Arctic would have less effect on the Earth's radiation budget than an equal albedo change over an equally large region located elswhere on the globe. Much less effect, I think, though I doubt I could do the calculus. So I think it's a mistake to use Wadhams' numbers as a basis for further calculation, as in Artful Dodger at 16:55. I think Wadhams, at least in this case, is an example of what Twemoran at 21:40 suggests we need: an alarmist. Wadhams is wrong, but he got headlines. (P.S. it would be much more convenient to refer to other people's comments if they were numbered. Neven?)
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Sep 7, 2012