Global Warming

Who Will Be Under Water as the Seas Rise

Every global shore touches the ocean, and the ocean is rising.

Climate Central just completed a novel analysis of worldwide exposure to sea level rise and coastal flooding. We found that 147 to 216 million people live on land that will be below sea level or regular flood levels by the end of the century, assuming emissions of heat-trapping gases continue on their current trend. By far the largest group — 41 to 63 million — lives in China. The ranges depend on the ultimate sensitivity of sea level to warming.

But even these figures may be two to three times too low, meaning as many as 650 million people may be threatened.

People living on land that will be below sea level or chronic flood levels by the end of the century, assuming current emissions trends continue, and medium sensitivity of sea level to warming. Some countries, such as the Netherlands, have levees that may provide protection. For the list ranked by percent exposure, we considered only countries with total populations over 1 million.

Our analysis relied on global data on elevation and population, but our experience using similar data in the U.S. strongly suggests that this global data is not as accurate or precise as more modern data sources. Comparing results for U.S. vulnerability using global data and state-of-the-art domestic data, we found that global elevation data led to major underestimates compared to modern U.S. elevation data (by a factor of 3 to 4), whereas global population data led to overestimates by a factor of 1.6 to 1.8. The net effect of global data was underestimation by a factor of 2 to 3.

If the overall error factors we calculated for the U.S. apply globally, then 300 to 650 million people live on land that will be submerged or exposed to chronic flooding, by 2100, under current emission trends.

Higher-quality global data — and in particular, elevation data — is needed to help resolve those figures — and makes a bigger difference than resolving sea level sensitivity. But our unadjusted results still give an indication of how nations compare in the threats they face from rising seas.

The top-20 list of most exposed countries includes representatives from every continent except Australia. The top seven slots, and 12 overall, come from Asia. Five European Union members make the list, as do the U.S., Brazil, and Nigeria.