A 2006 aerial view of a meltwater lake on the surface of the Greenland Ice Sheet, 60 miles southeast of Illulissat, reveals crevasses lined with dust particles from soil, soot and meteorite debris. Meltwater puddles into lakes such as these and eventually falls downward, through channels in the ice called moulins. Melting has occurred dozens of miles further inland and hundreds of feet higher than just a quarter century ago, according to the Extreme Ice Survey.
Greenland's ice locks up enough water to raise global sea levels more than 20 feet. Warming on that scale would take centuries.
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