How a massive ice shelf buttressed the last ice age's glaciers—and what it could mean for Antarctica today

About 20,000 years ago, an enormous, floating ice shelf more than a mile (1.6 kilometers) thick helped lock in three of the largest ice sheets in northern Canada and Greenland. When that ice shelf disappeared, it helped unlock part of these ice sheets, which contributed to hundreds of feet of sea level rise, establishing modern coastlines as we know them.

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