March 4, 2026

expert reaction to paper saying coastal sea levels are higher than assumed

A study published in Nature looks at costal sea levels. 

Dr Matt Palmer, Science Fellow at the Met Office Hadley Centre and Associate Professor at the University of Bristol, said:

“This is a very important paper that finds widespread underestimation of the coastal flood impacts associated with projections of sea-level rise. On average, the height of sea level is underestimated by 0.3m, which represents a large fraction of the projected rise to 2100. 

“Of even greater concern is the underestimation of sea-level height by up to 1m in the Global South, where huge coastal populations live alongside the threat from extreme waves and storm surges. 

“This means that the impacts of sea-level rise under climate change have been systematically underestimated. Put another way, we could see devastating impacts from coastal flooding earlier than expected from climate projections – particularly in the Global South. 

“The paper raises important questions on the need for interdisciplinary expertise and guidance in sea-level rise impacts assessments. The work also suggests a need for more comprehensive world-wide sea level observations to anchor future impacts modelling.” 

Prof Robert Nicholls, Professor of Climate Adaptation at the Tyndall Centre for Climate Change Research, University of East Anglia (UEA), said:

“This paper addresses an important dimension of sea-level science which has not received sufficient attention over the last few years and deserves systematic improvement. While the results are based on inference from a review of a large set of literature the conclusions that are drawn are reasonable. However, it should be remembered that the quality of vertical elevation data has improved dramatically over the last 15 years or so. A 30cm error sounds significant today, but 15 years ago it was much less surprising given the quality of the data.

“It is also important to remember that the errors discussed here influence our understanding of contemporary sea levels and their associated hazards. The influence of these results on the effects of climate change and sea-level rise are significant but indirect – they raise the baseline on which these changes occur. Further the risks due to sea-level rise depend on multiple factors and additional issues such as the present and future level of adaptation need to be considered to understand these risks. In the real world this means that present exposure to coastal hazards is higher than widely assumed – but not necessarily the level of coastal risk. These results also emphasise the threat of sea-level rise and climate change and the need for appropriate adaptation.”

Dr Alex Arnall, Associate Professor in Environment and Development at the University of Reading, said:

“If these revised exposure estimates are correct, the importance lies in what they mean for people living on low-lying coasts. The paper suggests that underestimation has been greatest in parts of the Global South, where small differences in relative sea level can translate into very large increases in the number of people counted as exposed. That matters because many of these regions have fewer financial and institutional resources to invest in coastal defences or to support alternative livelihoods. For poorer coastal communities, higher exposure doesn’t just mean more land below sea level. It means greater strain on homes, incomes and local economies, and fewer options for responding to the changes ahead.”

Prof Andrew Shepherd, Director of the Centre for Polar Observation and Modelling, Northumbria University, said:

“Sea levels are much higher than we had thought – about 30 cm higher – due to the swell of ocean currents. This means that 80 million people are living below sea level today, 50 million more than we had realised. Although this is bad news, it raises an important question: how do these communities cope – especially where sea defences have not been built? With around a metre of further sea level rise already locked in from existing global warming, what they are doing today may be exactly what the rest of the world needs to learn.”

Dr Natasha Barlow, Technical Director, Costal Resilience, Haskoning engineering consultancy, said:

“This study highlights the continuing need for consistent treatment of datasets, so they are comparable and use the same reference points. Transitions from national reference points (datums) to global datums, along with varied use of satellite data, GPS and models, mean this has not always been applied consistently or accurately, as demonstrated in the authors’ detailed assessment.

“The study focuses on global datasets, which are valuable for providing a broad picture of climate‑related hazards and risks. However, these datasets carry considerable uncertainty because of the limited precision achievable when estimating land‑level elevation at a global scale. They often assume coastal flooding behaves like a simple ‘bathtub’ model. Such global elevation models cannot account for the detailed factors essential in city‑, community‑ or region‑scale flood assessments; for example, interconnected water systems and groundwater storage, coastal erosion, or the socio‑economic circumstances that shape people’s ability to respond to flooding and adapt to climate change.

“The authors also emphasise an important point: these issues disproportionately affect the Global South. This is due not only to inconsistent application of reference points in coastal datasets, but also to limited availability of high‑quality elevation data (such as LIDAR) needed for accurate regional and local flood‑risk estimates. Many densely populated delta and estuary regions in the Global South face significant risk from sea‑level rise while lacking the resources required to respond effectively to increasing flood hazards.”

Prof Jonathan Bamber, Director of the Bristol Glaciology Centre, University of Bristol, said:

“Sea level rise (SLR) is one of most serious and certain consequences of global heating. It is a field I have worked in for some two decades and I was genuinely surprised by the results of this study, which is not about reassessing how much SLR there might be in the future but about using the correct estimate of present-day sea level. This might seem obvious, but unless practitioners and others working in the field understand the nuances of the different types of reference surfaces used and how they relate to coastal sea level it is easy to miscalculate the offset between coastal elevation and the sea surface height in that location.

“What the authors demonstrate is that in the majority of impact studies, that is exactly what has happened. The wrong assumptions are made about what present-day sea level is and it turns out that it has generally been underestimated in key sensitive coastal areas. This has important implications for impacts of future SLR in terms of the area and number of people potentially affected in low lying areas such as south east Asia and the Nile delta. It does not affect how much SLR might occur in the future.

“The authors estimate that the offset between the true sea surface height and that used in impact studies is around 24-27 cm. To put that in context, that is more than the total SLR that has occurred since the beginning of the 20^th century. They highlight an important limitation in most coastal impact studies but their conclusions about how this will affect estimates of future coastal inundation are less certain. First, they assume a higher accuracy for estimates in mean sea surface height at the coast than is actually the case. The best way to assess this is against tide gauge data, which are actually located at the land/ocean boundary. Second, the elevation of the land surface in the coastal zone has relatively large errors, which compounds the difficulty in determining the relative difference between the height of the land and sea at the coast.”

Prof Daniela Schmidt, Professor of Earth Sciences, University of Bristol, said:

“Methodological improvements of sea level rise are important due to the concentration of people, settlements, infrastructure and biodiversity hotspot in these places where land meets the sea. The study claims to quantify  SLR impacts and coastal hazard assessment. Like so many others, it solely sees the impact of sea level rise and the resulting losses and damages on people via land loss and impacts on settlements. These are important and need long term consideration such as the impact of sea level rise on the Thames Estuary and potential need for further infrastructure. The timing for adaptation options will ultimately depend on the rate of sea level change, something this paper is not addressing. 

“But coastal sea level rise will also alter our coastlines, result in erosion, and destroy important ecosystems which in turn also provide protection for our coastlines. It is fundamental to sea level rise projections consider the losses holistically and consider the impact drowning our wetlands and mudflats, or losing mangroves and coral as they cannot keep up with sea level rise, will have on natures ability to draw down CO2, to protect the costs and to nourish humans and biodiversity. No risk assessment is complete without a more holistic view.”

‘Sea level much higher than assumed in most coastal hazard assessments’ by Katharina Seeger & Philip Minderhoud was published in Nature at 4pm UK time on Wednesday 4 March 2026. 

DOI: https://doi.org/10.1038/s41586-026-10196-1

Declared interests

Andrew Shepherd: “No competing interests.”

Jonathan Bamber “is a professor of Earth Observation and glaciology at the University of Bristol and a visiting fellow at the Technical University Munich (TUM) and receives funding from the European Space Agency on a study aimed at closing the sea level budget globally and regionally. He also receives funding from TUM on coastal sea level and the EU on glaciers and ice sheets.”

Daniela Schmidt: “No competing interests”

Natasha Barlow “is Technical Director at Haskoning, a global engineering and environmental consultancy whose clients include coastal communities, policy makers, and authorities facing risks from sea‑level rise. Natasha previously spent 20 years as an academic. She has no conflict of interest in this study and had no involvement in the work. While Haskoning uses datasets of this kind in its projects, Natasha’s perspective on the research reflects her own experience of addressing complex local and regional challenges and the importance of using the highest‑quality datasets in hazard assessment.”

Alex Arnall: “I have no competing interests to declare.”

Matt Palmer: I declare no competing interests”

For all other experts, no reply to our request for DOIs was received.