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[laughter]

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If CO2 is overheating Greenland, why is

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the ice still over 10,000 feet thick?

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This is a really good question, because it addresses the concept of thickness,

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which is extremely important to polar scientists.

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It's very easy to see that ice sheets and ice shelves and sea ice are changing

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in a sort of spatial sense, but what's even more important

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is that they are also thinning. It's very important for sea ice,

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but it's also important for the ice sheets.

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We know from satellite data and mosaics of that satellite data

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that our sea ice extent is decreasing in this sense, the sort of planar sense,

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and our ice sheets calve off so we lose mass in that extent as well.

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But more importantly, we're getting thinning.

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Both in the sea ice and in the ice sheets and you can imagine

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that just a little bit of thinning spread over the scale of a continent amounts to a lot of water.

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So it's a great question, but I think we just have to fine tune the questioner's expectations.

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If I were to walk outside on a really cold day, it would take a little bit of time

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for my core body temperature to drop even though I am feeling chilly on the outside.

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That's what's happening in Greenland as well. The Greenland ice sheet is really thick.

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It's going to take a lot of time to melt all of that ice.

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So the Greenland ice sheet is thinning, and it's thinning variably but mostly along the coastlines.

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It's thinning beyond our expectations and all of that thinning is taking place upstream of where the ice sheet is grounded.

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Therefore that is going right into the ocean and contributing to mean sea level rise.

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