Future sea level rise due to the melting of the Greenland and Antarctic ice sheets could be substantially larger than estimated, according to new research from the University of Bristol. The study is the first of its kind on ice sheet melting to use structured expert elicitation (EE) together with an approach that mathematically pools experts' opinions. EE is already used in a number of other scientific fields such as forecasting volcanic eruptions.

The ice sheets covering Antarctica and Greenland contain about 99.5 percent of the Earth's glacier ice that would raise global sea level by some 63 m if it were to melt completely. The ice sheets are the largest potential source of future sea level rise – and they also possess the largest uncertainty over their future behavior. They present some unique challenges for predicting their future response using numerical modeling and, as a consequence, alternative approaches have been explored.

One such approach is via carefully soliciting and pooling expert judgments – a practice already used in fields as diverse as eruption forecasting and the spread of vector borne diseases. In this study, such an approach was used to assess the uncertainties in the future response of the ice sheets.

The median estimate for the sea level contribution from the ice sheets by 2100 was 29 cm with a 5 percent probability that it could exceed 84 cm. When combined with other sources of sea level rise, this implies a conceivable risk of a rise of greater than 1 m by 2100, which would have deeply profound consequences for humankind. The researchers also found that the scientists, as a group, were highly uncertain about the cause of the recent increase in ice sheet mass loss observed by satellites, and equally unsure whether this was part of a long-term trend or due to short-term fluctuations in the climate system.