"Ice Sheets", by Randall Munroe, licensed under Creative Commons Attribution-NonCommercial 2.5 License
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Data adapted from 'The Laurentide and Innuitian ice sheets during the Last Glacial Maximum' by A.S. Dyke et. al., which was way better than the sequels 'The Laurentide and Innuitian ice sheets during the Last Glacial Maximum: The Meltdown' and 'The Laurentide and Innuitian ice sheets during the Last Glacial Maximum: Continental Drift'.