Greenland Warming at Last Deglaciation: the Younger-Dryas Not So Cold

by Emil Morhardt

I’ve been blogging recently about papers that claim the thousand-year cessation of global warming in the midst of the last deglaciation—known as the Younger-Dryas (Y-D)—was triggered by a comet. Buizert et al.’s (2014) paper on Y-D temperature changes doesn’t address the comet question, but another equally interesting one: why did the sudden reversal of temperature 12,800 years ago (whatever it was triggered by) cause the temperature to plunge clear back to what it was before any warming had started? That’s what the relative deuterium and oxygen-18 concentrations from the Greenland Ice Sheet ice cores imply—more about that in a moment. Nevertheless, it seemed unlikely because at the time of the Y-D, a considerable amount of CO2 had accumulated in the atmosphere and Antarctica was warming apace. The answer, according to this paper is that temperatures did not cool down so much after all; things cooled off for sure, and warming was delayed for another thousand years, but at the depth of the Y-D cooling most of Greenland was on the order of 4˚C warmer than it had been 4,000–5,000 years before—but still quite cold. Continue reading