Sea-level rise: What the experts expect

In the long run, sea-level rise will be one of the most serious consequences of global warming. But how fast will sea levels rise? Model simulations are still associated with considerable uncertainty – too complex and varied are the processes that contribute to the increase. A just-published survey of 90 sea-level experts from 18 countries now reveals what amount of sea-level rise the wider expert community expects. With successful, strong mitigation measures, the experts expect a likely rise of 40-60 cm in this century and 60-100 cm by the year 2300. With unmitigated warming, however, the likely range is 70-120 cm by 2100 and two to three meters by the year 2300.

IMG_4484Complex problems often cannot simply be answered with computer models. Experts form their views on a topic from the totality of their expertise – which includes knowledge of observational findings and model results, as well as their understanding of the methodological strengths and weaknesses of the various studies. Such expertise results from years of study of a topic, through ones own research, through following the scientific literature and through the ongoing critical discussion process with colleagues at conferences.

For many topics it would be interesting for the public to know what the expert community thinks. If I had a dangerous disease, I would give a lot to learn what the best specialists from around the world think about it. Mostly, however, this expertise is not transparent to outsiders. The media only offer a rather selective window into experts’ minds.

More transparency can be achieved through systematic surveys of experts. The International Council of Scientific Academies (InterAcademy Council, IAC) in its review of IPCC procedures recommended in 2010: “Where practical, formal expert elicitation procedures should be used to obtain subjective probabilities for key results”. We took this advice and last November conducted a broad expert survey on future sea-level rise, in the context of a research project funded by NOAA. Lead author is Ben Horton (Rutgers University), the further authors are Simon Engelhart (University of Rhode Island) and Andrew Kemp (Tufts University).

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