| Summary: | Greenland ice core water isotopic composition (δ¹⁸O) provides detailed evidence for abrupt climate changes, but is by itself insufficient for quantitative reconstruction of past temperatures and their spatial patterns. We investigate Greenland temperature evolution during the last deglaciation using independent reconstructions from three ice cores and simulations with a coupled ocean-atmosphere climate model. Contrary to the traditional δ¹⁸O interpretation, the Younger Dryas period was 4.5±2°C warmer than the Oldest Dryas, due to increased CO₂ forcing and summer insolation. The magnitude of abrupt temperature changes is larger in central Greenland (9-14°C) than in the northwest (5-9°C), fingerprinting a North-Atlantic origin. Simulated changes in temperature seasonality closely track changes in the Atlantic overturning strength, and support the hypothesis that abrupt climate change is mostly a winter phenomenon.
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