Global sea levels could rise 6 feet by year 2100, twice as high as previous estimates

A new study on polar ice sheet melt warns that global sea levels could rise by almost six feet by the year 2100, an estimate twice as high as previously predicted.

The newly modeled sea level rise would devastate parts of major cities around the globe, and displace hundreds of millions of people.

The study was published Monday in the Proceedings of the National Academy of Sciences [PNAS] journal [Link].

Here's an excerpt:

Future sea level rise (SLR) poses serious threats to the viability of coastal communities, but continues to be challenging to project using deterministic modeling approaches. Nonetheless, adaptation strategies urgently require quantification of future SLR uncertainties, particularly upper-end estimates. Structured expert judgement (SEJ) has proved a valuable approach for similar problems. Our findings, using SEJ, produce probability distributions with long upper tails that are influenced by interdependencies between processes and ice sheets. We find that a global total SLR exceeding 2 m by 2100 lies within the 90% uncertainty bounds for a high emission scenario. This is more than twice the upper value put forward by the Intergovernmental Panel on Climate Change in the Fifth Assessment Report.

Despite considerable advances in process understanding, numerical modeling, and the observational record of ice sheet contributions to global mean sea-level rise (SLR) since the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change, severe limitations remain in the predictive capability of ice sheet models. As a consequence, the potential contributions of ice sheets remain the largest source of uncertainty in projecting future SLR. Here, we report the findings of a structured expert judgement study, using unique techniques for modeling correlations between inter- and intra-ice sheet processes and their tail dependences. We find that since the AR5, expert uncertainty has grown, in particular because of uncertain ice dynamic effects.

Clara Nugent, reporting for Time on the new study:

The upper limit for sea level rise by 2100 has previously been estimated between 1.7 and 3.2ft. – the range given in the fifth assessment report from the Intergovernmental Panel on Climate Change (IPCC), the leading international body for the assessment of climate change, in 2013. But many scientists believe that was a conservative estimate. The rate of glacier melt in Greenland and Antarctica is accelerating, and the authors of the report say current prediction models don’t account for significant uncertainties in how melting ice sheets could affect sea level rise.

To get a better understanding, an international group of researchers compiled a “structured expert judgement study,” using expert understanding of what is happening to glaciers to predict a broader range of possibilities than those considered in the IPCC report.

Read the study:
Ice sheet contributions to future sea-level rise from structured expert judgment
Jonathan L. Bamber, Michael Oppenheimer, Robert E. Kopp, Willy P. Aspinall, and Roger M. Cooke