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Greenland ice-core ¿>180-temperature reconstructions suggest a dramatic cooling during the Younger Dryas (YD; 12.9-11.7 ka), with temperatures being as cold as the earlier Oldest Dryas (OD; 18.0-14.6 ka) despite an approximately 50 ppm rise in atmospheric C02. Such YD cooling implies a muted Greenland climate response to atmospheric C02, contrary to physical predictions of an enhanced high-latitude response to future increases in CO,. Here we show that North Atlantic sea surface temperature reconstructions as well as transient climate model simulations suggest that the YD over Greenland should be substantially warmer than the OD by approximately 5°C in response to increased atmospheric C02. Additional experiments with an isotope-enabled model suggest that the apparent YD temperature reconstruction derived from the ice-core <5180 record is likely an artifact of an altered temperature-a180 relationship due to changing deglacial atmospheric circulation. Our results thus suggest that Greenland climate was warmer during the YD relative to the OD in response to rising atmospheric C02, consistent with sea surface temperature reconstructions and physical predictions, and has a sensitivity approximately twice that found in climate models for current climate due to an enhanced albedo feedback during the last déglaciation. [ABSTRACT FROM AUTHOR]

Greenland ice-core ¿>180-temperature reconstructions suggest a dramatic cooling during the Younger Dryas (YD; 12.9-11.7 ka), with temperatures being as cold as the earlier Oldest Dryas (OD; 18.0-14.6 ka) despite an approximately 50 ppm rise in atmospheric C02. Such YD cooling implies a muted Greenland climate response to atmospheric C02, contrary to physical predictions of an enhanced high-latitude response to future increases in CO,. Here we show that North Atlantic sea surface temperature reconstructions as well as transient climate model simulations suggest that the YD over Greenland should be substantially warmer than the OD by approximately 5°C in response to increased atmospheric C02. Additional experiments with an isotope-enabled model suggest that the apparent YD temperature reconstruction derived from the ice-core <5180 record is likely an artifact of an altered temperature-a180 relationship due to changing deglacial atmospheric circulation. Our results thus suggest that Greenland climate was warmer during the YD relative to the OD in response to rising atmospheric C02, consistent with sea surface temperature reconstructions and physical predictions, and has a sensitivity approximately twice that found in climate models for current climate due to an enhanced albedo feedback during the last déglaciation. [ABSTRACT FROM AUTHOR]