Scientists now estimate that more than 200 million people could be living on land that will fall below future coastal high-tide lines, based on new elevation data published in Nature Communications. Because much of this sea-level rise is already locked in by past emissions, experts warn the threat is effectively unstoppable for at least the next few decades. The latest research traces how the numbers jumped so sharply, who is most exposed, and why even ambitious climate policies will not fully prevent a massive reshaping of the world’s coasts.
The Science Behind the Surge in Estimates
The most dramatic shift in understanding came when researchers behind the CoastalDEM model corrected a long-known bias in the Shuttle Radar Topography Mission, or SRTM, elevation data. SRTM tended to mistake rooftops and tree canopies for bare ground, which meant earlier maps systematically overstated how high coastal communities sit above the sea. By using machine learning to build CoastalDEM on top of SRTM, the team at Core Introduces produced a far more accurate global coastal elevation dataset and found that about 190 million people live on land that is projected to fall below average high-tide lines by 2100 under a relatively low emissions pathway.
In that Nature Communications paper, the lead researcher described CoastalDEM as a major improvement in model accuracy because it better captures the vertical position of densely populated low-lying regions that older maps simply lifted too high. The study concluded that as many as 340 million people could be living on land that will be below projected annual flood levels by mid-century under high emissions, a finding that helped explain why previous estimates had been so low. That recalibration turned sea-level rise from a distant concern into a direct, quantifiable threat for hundreds of millions of people alive today.
Who and Where: Mapping the 200M+ at Risk
Follow-up work has sharpened the picture of who is most exposed. A separate Nature Communications analysis found that tropical regions account for a rapidly growing share of the threat, with the number of people in the tropics living below mean sea level projected to rise from about 18 million to roughly 92 million by 2100 as relative sea level climbs. That study, identified in the reporting as Primary, Reports that this surge in tropical exposure reflects both strong population growth and the fact that many tropical deltas and coastal plains are barely above the current sea surface.
Country-level visualizations based on the same Nature Communications research show that the largest exposed populations are concentrated in a handful of coastal nations, especially in Asia. A Convenient chart using the 200M-by-2100 figures highlights Indonesia, Bangladesh and several other Asian countries as leading hotspots. Parallel coverage by the Associated Press similarly emphasizes that the bulk of people living on land threatened by rising seas are in Asian megacities and river deltas, where dense coastal populations meet subsiding land and limited protective infrastructure.
Locked-In Threats: Why It’s Unstoppable by Mid-Century
The most sobering message from the science is that a large part of the risk is already baked in. Reporting on the CoastalDEM work explained that under current conditions roughly 150 million people are projected to be living on land below the average high-tide line by 2050, regardless of how quickly emissions fall over the next few years. As Major coverage put it, the new numbers effectively tripled earlier global estimates and showed that much of the coastal threat through mid-century is the result of past greenhouse gas emissions that have already warmed the oceans and set long-term ice melt in motion.
This sense of inevitability extends beyond people to critical infrastructure. A peer-reviewed assessment cited in Guardian reporting identified about 5,500 U.S. industrial and energy facilities that face a 100-year coastal flood risk by 2100 under a high-emissions scenario. That analysis, drawn from research labeled Primary, warned that even aggressive cuts in future emissions would not fully remove the hazard, because sea-level rise will continue for centuries as oceans expand and ice sheets respond to the heat already stored in the climate system.
Broader Impacts: Displacement and Hazardous Sites
Human exposure is only one dimension of the looming crisis. In a policy speech summarized by the United Nations, an Authoritative briefing warned that between 250 million and 400 million people could need new homes by 2100 if global sea level rise, or SLR, reaches between 1 and 1.6 meters. That estimate, described as Useful for framing security risks, casts the 200M-plus figure from CoastalDEM as part of a broader displacement wave that could strain housing, food supplies and political stability in dozens of countries.
Another line of peer-reviewed research has focused on what happens when rising water meets hazardous industrial and waste sites. A Nature Communications paper summarized in recent coverage examined how many toxic facilities and contaminated areas could be reached by coastal flooding by 2050 and 2100, and how that exposure changes under different emissions pathways. Follow-on reporting identified by editors as Major context and described as Good for explaining public-health stakes notes that flooding of these sites could mobilize pollutants into surrounding neighborhoods, compounding harms for already vulnerable communities. One expert quoted in that reporting warned that sea-level rise does not just threaten to inundate homes but may also turn nearby industrial zones into chronic sources of contamination.
Triangulating the Data: Multiple Studies Confirm Scale
The CoastalDEM findings are not the only evidence pointing to a vast at-risk population. A separate Major summary of a Nature Communications study described how researchers used high-resolution LiDAR measurements to estimate how many people live on land less than 2 meters above current sea level. That LiDAR-based analysis, highlighted as Helps for triangulating the literature, found that under roughly 1 meter of sea-level rise the number of people in that low-lying zone grows sharply, reinforcing the idea that small vertical changes in water level translate into very large jumps in exposure.
Across these different elevation models and scenarios, the broad range of projected long-term exposure runs from about 190 million people on land below 2100 high-tide lines under low emissions to roughly 340 million on land below projected annual flood levels under more pessimistic assumptions. Visualizations built from the Nature Communications datasets and shared in a Statista graphic explicitly link the headline figure of around 200 million people affected by 2100 to specific countries and regions, providing an Evidence trail that makes the scale of the threat easier to grasp. Taken together, these independent approaches suggest that while exact numbers will shift with future emissions and adaptation, the overall magnitude of the risk is not an outlier from a single model.
What Experts Say and What’s Uncertain
Security officials have started to treat sea-level rise as a geopolitical issue as much as an environmental one. In the same UN briefing that cited the 250 million to 400 million displacement estimate, a senior United Nations representative warned that whole small island states and low-lying coastal regions could face existential threats, with rising seas undermining sovereignty, food security and social cohesion. That official argued that unmanaged coastal retreat, combined with the pressures highlighted in the Nature Communications and CoastalDEM research, could fuel conflict and migration on a scale that current international systems are not prepared to handle.
At the same time, scientists stress that significant uncertainties remain around the exact pace of ice-sheet loss, the emissions pathway the world will follow and the effectiveness of local adaptation measures such as sea walls, zoning changes and managed retreat. Analysts quoted in Major reporting and other CoastalDEM coverage emphasize that while the lower bound of roughly 190 million people exposed by 2100 under low emissions is already alarming, stronger warming or weaker adaptation could push the total far higher. For now, experts say the most useful step governments can take is to publish clear, verifiable policy details, including specific emissions targets and coastal protection plans, so that communities living in the shadow of this unstoppable mid-century threat can see whether leaders are preparing for the water that is on the way.
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*This article was researched with the help of AI, with human editors creating the final content.
