Coastal flooding caused by storm surges and rising sea levels could threaten as much as 20% of the world's GDP by the end of the century without intervention to tackle climate change or help protect coastal regions, according to a new study from a group of international researchers.

The coasts of Northwest Europe, including the Southeast of England; the East coast of the United States; and India, particularly around the Bay of Bengal, are some of the regions that are particularly at risk, the study found.

The study, Projections of global-scale extreme sea levels and resulting episodic coastal flooding over the 21st Century, was published on Thursday in Scientific Reports, a Nature journal. It was a collaboration between researchers from the University of Melbourne, IHE Delt in the Netherlands, the University of Amsterdam, the University of East Anglia in the U.K., and Humboldt University in Berlin, Germany.

While the overall impact of rising sea levels has long led to dire warnings of the impacts of climate change, the study goes further in mapping out precise "hotspots" that are at risk, as well as the potential economic impact on infrastructure and economic activity in those coastal regions. It also charts in greater detail the impact of not just sea rise, but episodic flooding caused by strengthening storm events and tides, which is expected to be even more damaging, causing an estimated 69% of coastal flooding by 2100.

When it comes to the scale of that flooding, "one major finding is that what is now seen as a 100-year event could occur as frequently as every 10 years or less for most of the coastal locations," Ebru Kirezci, the lead author of the report and a PhD candidate in Ocean Engineering at the University of Melbourne, told Fortune.

The study doesn't account for efforts to reduce emissions, or flooding defenses like dykes and barriers that already exist, or are expected to be in place by the end of the century, the researchers said, and so is intended as a demonstration of the scale of the risks to populations and economies the world faces without intervention.

The proportion of the world's land affected by episodic flooding and rising seas in global "hotspots" alone, where the flooding is expected to be most severe, is expected to expand to a combined area larger than the total landmass of France, the study said. The proportion of the world's population and assets affected by coastal flooding is also expected to roughly double from current levels—up to 4.1% of the global population, and 20% of global GDP.

While the study did not attempt to forecast population or GDP growth, under the 2015 base model, the reach of that expanded coastal flooding would affect 287 million people, and assets and infrastructure worth $14.2 trillion.

However, the economic impacts of climate change and coastal flooding—alongside other disasters including raging wildfires—are already becoming clear. In April, Swiss Re, the insurance giant, said that weather-related natural disasters had a global economic cost of $1.618 trillion between 2010 and 2019. In 2017 and 2018 alone, insurers paid out a combined $218 billion in insurance for the economic impact of weather catastrophes.