Letter

Nature 437, 125-128 (1 September 2005) | doi:10.1038/nature03975; Received 7 March 2005; Accepted 29 June 2005

Modelled atmospheric temperatures and global sea levels over the past million years

Richard Bintanja1, Roderik S.W. van de Wal1 & Johannes Oerlemans1

  1. Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands

Correspondence to: Richard Bintanja1 Correspondence and requests for materials should be addressed to R.B. (Email: R.Bintanja@phys.uu.nl).

Marine records of sediment oxygen isotope compositions show that the Earth's climate has gone through a succession of glacial and interglacial periods during the past million years. But the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep-water temperature affect the recorded isotopic composition1, 2, 3, 4, 5. Separating these two effects would require long records of either sea level or deep-ocean temperature, which are currently not available. Here we use a coupled model of the Northern Hemisphere ice sheets6 and ocean temperatures, forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores, to quantify both contributions simultaneously. We find that the ice-sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima, suggesting that strong ocean cooling preceded slow ice-sheet build-up. The model yields mutually consistent time series of continental mean surface temperatures between 40 and 80° N, ice volume and global sea level. We find that during extreme glacial stages, air temperatures were 17 plusminus 1.8 °C lower than present, with a 120 plusminus 10 m sea level equivalent of continental ice present.

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