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 δ18O from GIS ice cores3,5 with δ18O from ice cores from small marginal icecaps. Contrary to the earlier interpretation of δ18O evidence from ice cores3,6, 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.
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We thank laboratory technician A. Boas, who meticulously performed most of the stable-isotope measurements presented in this paper during her 38 years at the Copenhagen stable isotope laboratory; W. Blake Jr for providing his insight, suggestions and corrections during the drafting of this paper; R. Greve for providing elevation data from his GIS modelling effort. B.M.V. thanks the Carlsberg Foundation for funding, and the Climatic Research Unit at University of East Anglia for hosting his research during all of 2007. V.L. and D.R. thank the Groupement de Recherche Européen (GDRE) Vostok (Institut national des sciences de l’Univers (INSU)/Centre national de la recherche scientifique (CNRS) for funding and Russian Foundation for Basic Research (RFBR)–CNRS grant 05-05-66801) for support.
This file contains Supplementary Notes, Supplementary Figures S1-S4 with Legends, Supplementary Tables S1-S2 and Supplementary References.