During the last prolonged warm spell on Earth, the oceans were at least four meters — and possibly as much as 6.5 meters, or about 20 feet — higher than they are now. Where did all that extra water come from? Mainly from melting ice sheets on Greenland and Antarctica, and many scientists, including University of Wisconsin-Madison geoscience assistant professor Anders Carlson, have expected that Greenland was the main culprit.

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