July 30, 2020

expert reaction to study on global sea level projections and coastal flooding over the 21st century

A study, published in Scientific Reports, looked at global sea level projections and coastal flooding over the 21st century.

Dr Robert Larter, Marine Geoscientist, British Antarctic Survey (BAS), said:

“This study explores how the combination of tides, storm surges and wave setup, superimposed on predictions of regional relative sea-level rise, will impact extreme sea levels and coastal flooding around the world.  The results imply large increases in the extent of coastal flooding by the end of the century, with substantial societal and economic impacts, with northwest Europe predicted to be one of the worst affected areas. For background sea-level rise, the authors used predictions from the 2013 5^th IPCC Assessment Report for medium and high emissions scenarios (RCP4.5 and RCP8.5, respectively). However, in the IPCC report it was acknowledged that the estimates of future sea-level rise did not encompass the full range of uncertainty and that collapse of marine-based sectors of the Antarctic ice sheet, if initiated, could cause global mean sea level to rise substantially above the stated ‘likely’ range during the 21st century. Some subsequent studies have estimated that under certain circumstances ice loss from Antarctica could contribute more than an additional metre to mean sea-level rise by 2100, more than doubling the worst case IPCC projections. Therefore, while the projections in this paper should be a cause for great concern, extreme sea levels by the end of the century could be even higher than this study predicts. The large uncertainty arising from future change in marine-based sectors of the Antarctic ice sheet highlights the importance of improving knowledge of how it will respond to climate change. This is why the UK Natural Environment Research Council and the US National Science Foundation, with collaboration from several other national Antarctic programmes, are funding the International Thwaites Glacier Collaboration, a major initiative to better constrain ongoing and future change affecting the most rapidly changing and most vulnerable large glacier in West Antarctica.”

Dr Natasha Barlow, Associated Professor, University of Leeds, said:

“The press release is a good summary of the scientific work conducted by the authors.  This is a global assessment risk of future sea level rise and storms, based upon a series of high quality datasets.  To conduct a global assessment, assumptions and simplifications have to be made, which the authors are realistic about.  The results allow ‘hot spot’ areas, at risk of significant future coastal inundation, to be identified.  These hot spots should form the basis of detail regional or local research to look at potential adaptation or coastal defence solutions.  Due to the need for simplification with this being a global analysis, some areas may be identified at high risk of future flooding, but current or planned measures e.g. coastal defences or adaptation, may mean this risk has been overstated.  Regional and local assessments of future coastal inundation, due to both sea-level rise and extreme events, are important.”

Dr Sally Brown, Deputy Head of Department, Department of Life and Environmental Sciences, Bournemouth University, said:

“This paper once again highlights the very real threat and costs of sea-level rise to millions of people living around the world. The paper provides some alarming headlines as risks are considered without adaptation or protection, but in reality there is adapting to rising sea-level rise. However, the human implications of these risks are still being explored and the potential catastrophic implications of inaction not fully appreciated at a local level. A greater emphasis of action needs to be considered for those affected and methods the reduce risk, so that these headlines do not become a reality.”

Professor Jim Hall FREng, Professor of Climate and Environmental Risks and Director of Research in the School of Geography and the Environment, University of Oxford, said:

“This is an impressive paper because, unlike many previous papers that have looked at the average effects of sea level rise, Kirezci et al. have carefully assembled data on the effects of tidal variations and storm surges, which can significantly raise water levels and lead to the most severe coastal floods. The authors have used these predictions of extreme water levels to identify coastal floodplains that are exposed to the effects of sea level rise. The results are not very surprising: low-lying places that are already at risk of flooding, like coastal Bangladesh, are set to be more at risk in future. The predictions of flood risk hotspots should be treated with care, as the risk mapping does not take account of the effects of engineered coast defences, which we know have been built to protect places like Rotterdam and Shanghai (two hotspots that are identified in the paper) from flooding during storm surges. The thorny questions of what standard coastal communities will need to be protected to in future, and whether that is affordable, are dodged in this paper.”

Prof Jonathan Bamber, Professor of Glaciology, University of Bristol, said:

“This study highlights the vulnerability of coastal assets and communities to future sea level rise and the associated flooding. The numbers in terms of human lives, and economic costs are enormous but could well be underestimates because of known biases in coastal topographic data. The projected economic cost in 2100, for example, is about ten times larger than forecasts of global GDP decline in 2020 due to the Covid-19 pandemic. What this study also shows is that the impacts of future sea level rise, like many other aspects of climate warming, will affect nations across the globe, some that will have the resources to adapt to the threats posed, like Northwest Europe, but many that will not such as Bangladesh and Pacific island states.”

‘Projections of global‑scale extreme sea levels and resulting episodic coastal flooding over the 21st century’ by Ebru Kirezci et al. was published in Scientific Reports at 16:00 UK time on Thursday 30 July.

DOI: https://doi.org/10.1038/s41598-020-67736-6

Declared interests

Dr Rob Larter: I declare an interest as a Principal Investigator or one of the research projects funded by the International Thwaites Glacier collaboration. However, I make no apology for trying to make a link between this paper to our ongoing work, as I think it is important to draw attention to the additional uncertainty in sea-level rise projections that stem from potential ice loss in Antarctica.

Dr Natasha Barlow:  No declarations

Dr Sally Brown: No competing interests.

Prof Jim Hall: No declarations of interest.

Prof Jonathan Bamber: I am funded to study the causes of recent sea level variations by the European Research Council.

None others received.