Extreme storm surges are occurring twelve times more frequently today than in 1900, new analyzes show. Accordingly, such “floods of the century” only occurred once every 100 years back then, but today they occur on a global average every eight years. The main causes of the increasingly extreme storm surges are man-made climate change and sea level rise, as climate researchers have determined. This anthropogenic contribution to extreme water levels has quadrupled since 1900, while natural factors have lost influence.
Climate change is driving global sea levels higher and faster. In the 20th century alone, average levels rose by around 15 centimeters and almost four millimeters are added every year. As a result, flood levels are rising and storm surges are running higher. Flat coastal areas are already experiencing flooding more and more frequently, and many South Sea islands could soon be uninhabitable. According to forecasts, more than 360 million people could be at acute risk from land loss and increasingly frequent flooding by 2100.
“But a fundamental question has so far remained unanswered: How much has man-made climate change already increased the frequency of extreme water levels?” explain Sönke Dangendorf from Tulane University in New Orleans and his colleagues. To clarify this, they evaluated the level data from around 130 measuring stations around the world since 1900 and linked them to climate simulations. This enabled them to determine how frequently extreme events such as once-in-a-century floods occur today compared to before and what the causes are.
Twelve times more extreme storm surges than before
The analyzes showed: “The average frequency of a once-in-a-century flood has increased twelvefold since 1900,” report Dangendorf and his team. Water levels that previously only occurred once a century during storm surges now occur every eight years on a global average. “Such extreme water levels occur when spring tides, storms and rising sea levels come together,” says Dangendorf. “As water levels rise, even weaker storms can cause severe storm surges.”
Since 1900, the global average sea level has risen by around 20 centimeters, meaning that storm surges now start from this higher initial level. “Many people underestimate what 20 centimeters of sea level rise means: In the event of a storm surge, these 20 centimeters don’t just come on top – they shift the entire starting point,” explains co-author Ben Marzeion from MARUM – Center for Marine Environmental Sciences at the University of Bremen.
However, the enormous increase in once-in-a-century floods by a factor of twelve is worrying, says Marzeion. “This shows how much even moderate sea level rise can change the frequency of storm surges and extreme water levels.”
Human influence as the main cause
But what are the causes of the increasingly frequent floods of the century? The researchers used their climate simulations to determine the role that various influencing factors play. In these, they used various scenarios to check the contribution of anthropogenic climate change and sea level rise, land subsidence and natural climate and sea level fluctuations to the extreme floods.
The result: The biggest driver of rising sea levels and the increase in extreme storm surges is human influence. The team determined that, on average, it is responsible for a sea level rise of around 0.77 millimeters per year over the last 100 years. In contrast, natural factors only accounted for around 0.48 millimeters per year, and land subsidence around 0.36 millimeters per year. “People are one factor among many,” says Marzeion. “But man-made sea level rise is now the most important reason for the increase in such extreme events.”
According to the calculations, the influence of anthropogenic factors alone has more than quadrupled the frequency of extreme storm surges since 1900. This has become particularly clear since 1970: Since then, the influence of anthropogenic factors has continued to increase, while the proportion of natural causes has decreased.
Consequences for coastal protection
“These results provide us with robust, observational evidence that climate change has already transformed storm surge risk on coasts worldwide,” write Dangendorf and his colleagues. “This change is not a distant future forecast for 2050 or 2100, but is already underway.” This underlines the need for rapid adjustments in order not to allow the risk to grow any further. In some coastal regions it may even be necessary to relocate people if coastal protection is no longer sufficient.
What does this mean for the German sea coasts? As the team emphasizes, the focus of their analyzes was on the global situation. Nevertheless, northern Germany is also affected by these developments, where storm surges are becoming ever higher. “It is crucial for coastal protection that historical experience no longer applies. We must respond to this with early planning for adaptation,” says Marzeion.
Source: Sönke Dangendorf (Tulane University) et al., Nature Climate Change, 2026; doi: 10.1038/s41558-026-02659-0