BBC Climate change: Global sea level rise could be bigger than expected

Scientists believe that global sea levels could rise far more than predicted, due to accelerating melting in Greenland and Antarctica.

The long-held view has been that the world’s seas would rise by a maximum of just under a metre by 2100.’  This new study (see insert), based on expert opinions, projects that the real level may be around double that figure.

Future sea level rise (SLR) poses serious threats to the viability of coastal communities, but continues to be challenging to project using deterministic modelling 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.

https://www.pnas.org/content/early/2019/05/14/1817205116

BBC ‘This could lead to the displacement of hundreds of millions of people, the authors say.

The question of sea-level rise was one of the most controversial issues raised by the Intergovernmental Panel on Climate Change (IPCC), when it published its fifth assessment report in 2013.

It said the continued warming of the planet, without major reductions in emissions, would see global waters rising by between 52cm and 98cm by 2100.

Many experts believe this was a very conservative estimate. Ice scientists are also concerned that the models currently used to predict the influence of huge ice sheets on sea levels don’t capture all of the uncertainties about how these are now melting.

Judgement day

To try to get a clearer picture, some of the leading researchers in the field carried out what is termed a structured expert judgement study, where the scientists make predictions based on their knowledge and understanding of what is happening in Greenland, West and East Antarctica. In the researchers’ view, if emissions continue on the current trajectory then the world’s seas would be very likely to rise by between 62cm and 238cm by 2100. This would be in a world that had warmed by around 5C – one of the worst-case scenarios for global warming.

“For 2100, the ice sheet contribution is very likely in the range of 7-178cm but once you add in glaciers and ice caps outside the ice sheets and thermal expansion of the seas, you tip well over two metres,” said lead author Prof Jonathan Bamber from the University of Bristol.