Sea levels are much higher than we thought. Real-world oceans are making a mockery of flood-risk forecasts based on crude global modeling. And to make matters worse, coastal lands almost everywhere are subsiding faster than anyone realized — often many times faster than the seas are rising. This combination of rising sea levels and sinking coastal lands is a recipe for disaster.

These findings come from two major new studies that are reshaping our understanding of the threats posed by rising tides and sinking land and underlining the imminent risk of inundation facing tens of millions of people in some of the world’s largest megacities, say researchers not involved in the studies.

“The impacts of sea level rise under climate change have been systematically underestimated,” concludes Matt Palmer, a specialist on sea level rise at the U.K. Met Office’s Hadley Centre for Climate Science. “We could see devastating impacts much earlier than predicted — particularly in the Global South.”

“Taken jointly, these two papers paint a considerably more concerning picture than either would in isolation,” says Franck Ghomsi, an oceanographer at the University of Cape Town. “We are seeing an emerging body of research that rewrites the story of coastal vulnerability.”

Around 80 million people are today living on land in coastal areas below sea level — almost twice previous estimates.

It has long been known that sea levels vary a lot globally, and have been rising more in some places than others. But now a groundbreaking Dutch analysis of actual sea levels as measured by tidal gauges has found that almost the entire scientific literature has dramatically underestimated current sea levels, showing the threats posed by rising sea levels and sinking coastal lands.

Katharina Seeger and Philip Minderhoud, geographers at Wageningen University & Research, in the Netherlands, say seas are on average almost 1 foot higher than standard estimates, which are based on global models that assume calm seas and ignore ocean currents and the effect of winds. Sea levels are not rising faster than thought, but the baseline for future rise is considerably higher in most places.

In many of the 385 cases the pair examined, previously accepted sea levels are 3 feet or more off — almost all of them too low. They conclude that around 80 million people are today living on land in coastal areas below sea level — almost twice previous estimates — dramatically increasing the numbers at risk as sea level rise accelerates in the coming decades, demonstrating the dangers of the combined threat of rising sea levels and sinking coastal lands.

Read the full article about rising sea levels and sinking coastal lands by Fred Pearce at Yale Environment 360.