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An expert judgement assessment of future sea level rise from the ice sheets

Abstract

A major gap in predictive capability concerning the future evolution of the ice sheets was identified in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change. As a consequence, it has been suggested that the AR4 estimates of future sea-level rise from this source may have been underestimated. Various approaches for addressing this problem have been tried, including semi-empirical models and conceptual studies. Here, we report a formalized pooling of expert views on uncertainties in future ice-sheet contributions using a structured elicitation approach. We find that the median estimate of such contributions is 29 cm—substantially larger than in the AR4—while the upper 95th percentile value is 84 cm, implying a conceivable risk of a sea-level rise of greater than a metre by 2100. On the critical question of whether recent ice-sheet behaviour is due to variability in the ice sheet–climate system or reflects a long-term trend, expert opinion is shown to be both very uncertain and undecided.

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Figure 1: Shaded relief maps of Antarctica and Greenland showing regions of enhanced flow (in colour) and areas of the ice sheets grounded below sea level (hatched).
Figure 2: The PDF for the rate of SLR due to ice-sheet contributions by year 2100.
Figure 3: PDFs for the contributions of each ice sheet derived from the 2012 survey, combined as distributions using the performance weights (PerfWts) pooling option.
Figure 4: PDFs of the 2010 and 2012 response to the question related to whether the trends observed in the satellite record over roughly the past decade is due to internal variability or to a secular trend.

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Acknowledgements

We thank the experts who participated in the two surveys. Each is a pre-eminent scientist in the field, with many other demands on their time and expertise; their individual views are authoritative, and collectively invaluable. J.L.B. would like to thank M. New and J. Sky for their assistance with the first questionnaire and D. Vaughan for his comments on a draft of the paper. This work was largely funded by the European Commission’s 7th Framework Programme through grant number 226375 (ice2sea contribution number 129). W.P.A. was supported in part by an Advanced European Research Council grant to Prof RSJ Sparks (VOLDIES Project).

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J.L.B. conceived and carried out the study and solicited the expert judgements. W.P.A. analysed the elicitations and carried out the Monte Carlo simulations. Both authors wrote the paper.

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Correspondence to J. L. Bamber.

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The authors declare no competing financial interests.

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Bamber, J., Aspinall, W. An expert judgement assessment of future sea level rise from the ice sheets. Nature Clim Change 3, 424–427 (2013). https://doi.org/10.1038/nclimate1778

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