The multimillennial sea-level commitment of global warming
- aPotsdam Institute for Climate Impact Research, 14473 Potsdam, Germany;
- bInstitute of Physics, Potsdam University, 14476 Potsdam, Germany;
- cCollege of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331;
- dCenter for Climate and Cryosphere, Institute for Meteorology and Geophysics, University of Innsbruck, 6020 Innsbruck, Austria;
- eDepartment of Earth Sciences, University of Ottawa, Ottawa, ON, Canada K1N 6N5;
- fEarth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802;
- gUniversity of British Columbia, Vancouver, BC, Canada V6T 1Z4;
- hUniversidad Complutense de Madrid, 28040 Madrid, Spain; and
- iInstituto de Geociencias, Universidad Complutense de Madrid-Consejo Superior de Investigaciones Científicas, 28040 Madrid, Spain
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Edited by John C. Moore, College of Global Change and Earth System Science, Beijing, China, and accepted by the Editorial Board June 13, 2013 (received for review November 7, 2012)

Abstract
Global mean sea level has been steadily rising over the last century, is projected to increase by the end of this century, and will continue to rise beyond the year 2100 unless the current global mean temperature trend is reversed. Inertia in the climate and global carbon system, however, causes the global mean temperature to decline slowly even after greenhouse gas emissions have ceased, raising the question of how much sea-level commitment is expected for different levels of global mean temperature increase above preindustrial levels. Although sea-level rise over the last century has been dominated by ocean warming and loss of glaciers, the sensitivity suggested from records of past sea levels indicates important contributions should also be expected from the Greenland and Antarctic Ice Sheets. Uncertainties in the paleo-reconstructions, however, necessitate additional strategies to better constrain the sea-level commitment. Here we combine paleo-evidence with simulations from physical models to estimate the future sea-level commitment on a multimillennial time scale and compute associated regional sea-level patterns. Oceanic thermal expansion and the Antarctic Ice Sheet contribute quasi-linearly, with 0.4 m °C−1 and 1.2 m °C−1 of warming, respectively. The saturation of the contribution from glaciers is overcompensated by the nonlinear response of the Greenland Ice Sheet. As a consequence we are committed to a sea-level rise of approximately 2.3 m °C−1 within the next 2,000 y. Considering the lifetime of anthropogenic greenhouse gases, this imposes the need for fundamental adaptation strategies on multicentennial time scales.
Footnotes
- ↵1To whom correspondence should be addressed. E-mail: Anders.levermann{at}pik-potsdam.de.
Author contributions: A.L. designed research; A.L., P.U.C., B.M., G.A.M., D.P., V.R., and A.R. performed research; B.M., G.A.M., D.P., V.R., and A.R. contributed new reagents/analytic tools; and A.L. and P.U.C. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. J.C.M. is a guest editor invited by the Editorial Board.
See Commentary on page 13699.
Freely available online through the PNAS open access option.
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