A new study published earlier this month predicts a worst case scenario of sea level rise reaching two metres by 2100, reports Euronews. That is more than double the upper value put forward by the Intergovernmental Panel on Climate Change (IPCC) in their landmark 2013 Fifth Assessment Report (AR5). The AR5 predicted that sea levels would rise between 52 and 98 centimetres by 2100 under the warmer scenario contemplated, RCP8.5, which corresponds to temperature increases between 2.6 °C and 4.8 °C.
According to the lead author of the paper, Jonathan Bamber, from the School of Geographical Sciences at Bristol University, the worst case scenario is a low probability ─ 5% ─ but high impact scenario, that would ‘result in land loss of 1.79 M km2, including critical regions of food production, and displacement of up to 187 million people’. Unless measures are taken to reinforce the coasts, under this scenario parts of London, the northern coast of the Netherlands and Venice would be seriously affected. Across the Atlantic, portions of southern Florida and the Caribbean could disappear.
Predictions and uncertainty
The study involved 22 experts in ice sheet processes, and was published in Proceedings of the National Academy of Sciences of the United States of America. The authors explain that since the last IPCC report in 2013, significant progress has been made in understanding and modelling how ice sheets interact with the rest of the climate system, although serious limitations remain. The extent to which the Greenland and Antarctic ice sheets will melt is the main source of uncertainty when it comes to predicting sea level rise.
Under a +2 °C temperature scenario consistent with the Paris Agreement, the median estimated contribution of ice sheets to sea level rise would be 26 cm, with a 95th percentile value of 81 cm. Under a + 5 °C temperature scenario, more likely if current trends are maintained, the corresponding values are 51 and 178 cm, respectively. The total sea level rise estimates include also contributions from other sources, namely glacier mass loss, ocean thermal expansion from warming, and land water storage. Including all sources results in a global sea level rise estimate that exceeds 2 metres at the 95th percentile (5% probability).
Preparing for the future
The study results anticipate sea level rise well above the AR5 predictions. However, the findings cannot be compared directly with those from the AR5, because they involve different temperatures and percentiles. Dr Bamber explains that the bigger numbers are due to a combination of using a higher temperature rise scenario (+ 5 °C) and increased understanding of the interaction of ice sheets with climate over the past 6 years.
Sea level rise threatens coastal communities and ecosystems worldwide, and although the probability of a two-metre rise is low (5%), the consequences would be so profound that it should not be ruled out. Plans for adaptation measures are underway in several countries, including building or raising structures such as surge barriers and sea walls, enhancing nature-based defences such as wetlands, and retreat from areas threatened by flooding. Co-author Willy Aspinall hopes that ‘the study results can provide decision makers greater awareness of potential high-end sea level rise, which is crucial for robust decision making’.