Global sea levels could rise far more than previously predicted due to accelerating melting in Greenland and Antarctica, according to a new study. The findings project that the real sea level rise by 2100 could be double the 1m prediction posited by the Intergovernmental Panel on Climate Change (IPCC) when it published its fifth assessment report in 2013. 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 they are now melting. For this report, leading researchers in the field carried out “a structured expert judgement study,” in which scientists make predictions based on their knowledge and understanding of what is happening in Greenland, West and East Antarctica. In the group’s view, if emissions continue on the current trajectory then the world’s seas would probably rise by between 62cm and 238cm by 2100. This would be in an environment 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,” lead author Prof. Jonathan Bamber from the University of Bristol told the BBC. The IPCC report in 2013 only considered what is likely to happen, which in scientific terms means they looked at 17-83% of the range of possibilities. The new study looks at a broader range of results, covering 5-95% of the estimates. Major global cities, including London, New York and Shanghai would be under threat of extensive flooding in a worst scenario envisaged by the scientists. The authors acknowledge that the probability of hitting the high end of the range are around 5%, but they should not be discounted. “Even a 1% probability means that a one in a hundred-year flood is something that could happen in your lifetime. I think that a 5% probability, crikey -- I think that's a serious risk,” Prof. Bamber told the BBC. The study has been published in the journal Proceedings of the National Academy of Sciences.