One of the great ‘fears’ we have regarding global warming is the rise in sea level and the risk of floods in coastal locations in much of the world due to the melting of the poles. But now we have bad news: the vast majority of scientific studies on the risk of coastal flooding have started from the wrong premise. And it is not a miscalculation in the thaw or in the CO₂ emissionsbut we have been measuring wrongly where the ‘zero’ is.
They have realized. This is what has been revealed by a new study published this month March in Nature that has shaken the foundations of coastal climate projections. Here the research has pointed out that the sea level on the coasts is, on average, about 30 centimeters higher than what the risk models assumed. And in some areas of the planet, the difference exceeds one meter.
How is it possible? To understand where the problem is, you have to look at how a flood risk map is created. When researchers calculate which areas will be underwater if sea levels rise, they need a starting point like a baseline, and the problem is that this starting point was very wrong.
The problem. To reach this conclusion, the researchers reviewed 385 peer studies published between 2009 and 2025 and discovered a pattern: more than 90% of these investigations used “theoretical geoids” to mark this baseline. The problem is that a geoid is an idealized gravitational model of the Earth that assumes an ocean at perfect rest.
However, the real ocean is far from being completely at rest, since there are different factors, such as prevailing winds, ocean currents, water temperature and salinity, that cause water to accumulate more on some coasts than on others. That is why when the researchers compared these theoretical models with the real measurements obtained through satellite altimetry and tide gauges, the discrepancy was evident.
They change the world. At a global level, if this correction is adjusted to real factors, the underestimation of coastal sea level is between 24 and 30 centimeters. And although it may seem like a manageable figure, in coastal topography 30 centimeters makes the difference between a dry promenade and a flooded city.
The most worrying thing is the geographical inequality of this error, since, while in some areas of the global north the deviation is smaller, in the South the effective sea level becomes one meter or more higher than what had been projected. But there are even exceptional areas where extreme figures of up to 5.5 or 7.6 meters are reached.
Greater risk. By applying these new models of the seas, the Wageningen researchers discovered that, given a projected 1 meter rise in sea level, the coastal area at risk of flooding is 37% greater than previously thought, which puts an additional 132 million people in the danger zone.
The rhythm does not change. Although this may seem like we are experiencing an increase in the speed of sea level rise, the truth is that everything remains at the same point, and with a speed that remains the same as that at which it had been previously measured.
What changes in this case is the starting point, since by starting from a base that was too low we were experiencing a false sense of security. This means that we are now closer to the critical flood thresholds than we thought, so the time margin we thought we had to build dams, relocate populations or adapt infrastructure in megacities in Asia or on Pacific islands has just been drastically reduced.
The next step. To solve this historical “blind spot”, the research team has not limited itself to pointing out the error that has been made, but has processed the corrected data using supercomputers and published it openly. The goal here is for governments and climatologists to be able to recalculate their coastal risk maps using the actual sea surface and not a theoretical globe.
In Xataka | Someone has created a simulator where you can see if sea level rise is going to reach your house or not.
Image | Adam Dillon
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