Holocene thinning of the Greenland ice sheet

On entering an era of global warming, the stability of the Greenland ice sheet (GIS) is an important concern¹, especially in the light of new evidence of rapidly changing flow and melt conditions at the GIS margins². Studying the response of the GIS to past climatic change may help to advance our understanding of GIS dynamics. The previous interpretation of evidence from stable isotopes (δ¹⁸O) in water from GIS ice cores was that Holocene climate variability on the GIS differed spatially³ and that a consistent Holocene climate optimum-the unusually warm period from about 9,000 to 6,000 years ago found in many northern-latitude palaeoclimate records⁴-did not exist. Here we extract both the Greenland Holocene temperature history and the evolution of GIS surface elevation at four GIS locations. We achieve this by comparing delta O-18 from GIS ice cores(3,5) with δ¹⁸O from ice cores from small marginal icecaps. Contrary to the earlier interpretation of δ¹⁸O evidence from ice cores^3,6, our new temperature history reveals a pronounced Holocene climatic optimum in Greenland coinciding with maximum thinning near the GIS margins. Our δ¹⁸O-based results are corroborated by the air content of ice cores, a proxy for surface elevation⁷. State-of-the-art ice sheet models are generally found to be underestimating the extent and changes in GIS elevation and area; our findings may help to improve the ability of models to reproduce the GIS response to Holocene climate.