Facing a flooded future, the world’s vulnerable coastal cities will undergo sea-level rise worse than previously understood, according to a new corrective report by Climate Central.

As a result of heat-trapping pollution from human activities, rising sea levels could within three decades will push chronic floods higher than land currently home to 300 million people

By 2100, areas now home to 200 million people could fall permanently below the high tide line. These new figures are the result of an improved global elevation dataset produced by Climate Central using machine learning. That process has revealed that coastal elevations are significantly lower than previously understood across wide areas.

The threat is greatest in coastal Asia, according to the revised findings, and augur profound economic and political consequences within the lifetimes of people alive today

Most estimates of global mean sea-level rise in this century at below 2 meters. That calculation rests on a positive vertical bias of the principle digital elevation model (DEM) used to assess global and national population exposures to extreme coastal water levels through the Shuttle Radar Topography Mission (SRTM). That mission was an international research effort that obtained digital elevation models on a near-global scale (from 56°S to 60°N), to generate the most complete high-resolution digital topographic database of Earth prior to the release of the ASTER Global DEM in 2009.

However, a new technology is the CoastalDEM, using neural networks to reduce SRTM error. Applying the CoastalDEM, the new study shows that 190 million people (150–250 M, 90% confidence interval) currently occupy global land below projected high tide lines for 2100 under low carbon emissions. That estimate exceeds the previous calculation at from 110 million, for a median increase of 80 million.

These figures nearly triple the SRTM-based estimates. Under high carbon emissions, the CoastalDEM-based study indicates up to 630 million people live on land below projected annual flood levels for 2100 versus the previous count of roughly 250 million affected by 2100, and up to 340 million by 2050. The Climate Central report now estimates one billion people now occupy land less than 10 meters above current high-tide lines, including 250 million below 1 meter.

Download the report: Web Version and PDF

Findings are documented in a new peer-reviewed paper in the journal Nature Communications

Photo: Artists rendition of Miami Beach, Florida in 2050. Source: http://sealevel.climatecentral.org.