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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/tc-2020-89
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2020-89
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  16 Apr 2020

16 Apr 2020

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A revised version of this preprint is currently under review for the journal TC.

Large and irreversible future decline of the Greenland ice-sheet

Jonathan M. Gregory1,2,, Steven E. George1,, and Robin S. Smith1, Jonathan M. Gregory et al.
  • 1National Centre for Atmospheric Science, University of Reading, UK
  • 2Met Office Hadley Centre, Exeter, UK
  • These authors contributed equally to this work.

Abstract. We have studied the evolution of the Greenland ice-sheet under a range of constant climates typical of those projected for the end of the present century, using a dynamical ice-sheet model (Glimmer) coupled to an atmospheric general circulation model (FAMOUS-ice AGCM). The ice-sheet surface mass balance (SMB) is simulated by the AGCM, including its dependence on altitude within AGCM gridboxes. Over millennia under a warmer climate, the ice-sheet reaches a new steady state, whose mass is correlated with the initial perturbation in SMB, and hence with the magnitude of global climate change imposed. For the largest global warming considered (about +5 K), the contribution to global-mean sea-level rise (GMSLR) is initially 2.7 mm yr−1, and the ice-sheet is eventually practically eliminated (giving over 7 m of GMSLR). For all RCP8.5 climates, final GMSLR exceeds 4 m. If recent climate were maintained, GMSLR would reach 1.5–2.5 m. Contrary to expectation from earlier work, we find no evidence for a threshold warming that divides scenarios in which the ice-sheet suffers little reduction from those which it is mostly lost. This is because the dominant effect is reduction of area, not reduction of surface altitude, and the geographical variation of SMB must be taken into account. The final steady state is achieved by withdrawal from the coast in some places, and a tendency for increasing SMB due to enhancement of cloudiness and snowfall over the remaining ice-sheet, through the effects of topographic change on atmospheric circulation. If late twentieth-century climate is restored, the ice-sheet will not regrow to its present extent, owing to such effects, once its mass has fallen below a threshold of about 4 m of sea-level equivalent. In that case, about 2 m of GMSLR would become irreversible. In order to avoid this outcome, anthropogenic climate change must be reversed before the ice-sheet has declined to the threshold mass, which would be reached in about 600 years at the highest rate of mass-loss within the likely range of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

Jonathan M. Gregory et al.

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Jonathan M. Gregory et al.

Jonathan M. Gregory et al.

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Latest update: 21 Oct 2020
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Short summary
Melting of the Greenland ice-sheet as a consequence of global warming could raise global-mean sea-level by up to 7 m. We have studied this using a newly developed computer model. With recent climate maintained, sea-level would rise by 1.5–2.5 m over many millennia due to Greenland ice-loss. The warmer the climate, the greater the sea-level rise. Beyond about 3.5 m it would become partially irreversible. In order to avoid this outcome, anthropogenic climate change must be reversed soon enough.
Melting of the Greenland ice-sheet as a consequence of global warming could raise global-mean...
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