The findings are based on new artificial intelligence and data, nearly tripling the previously estimated area and threatened populations.
By 2050, land that is currently home to about 300 million people will fall below the elevation of the average annual coastal flood, which means they can face severe flooding at least once a year. By 2100, a land of 200 million people could be permanently seated below the tides, rendering these coastal areas almost impossible.
"The results show that yes, many more people are on vulnerable land than we thought," said Benjamin Strauss, one of the study's co-authors and CEO of the non-profit organization Climate Central. He added that these affected regions should take immediate action to avoid the impending "economic and humanitarian catastrophe".
Whole coastal cities may be deleted if there is insufficient maritime protection. According to the survey, about 70% of people at risk of flooding and persistent flooding are in eight Asian countries: China, Bangladesh, India, Vietnam, Indonesia, Thailand, Philippines and Japan.
The entire southern edge of Vietnam may be flooded, according to Climate Central forecasts.
This is not just about Asia – according to Climate Central, in 19 other countries, including Brazil and the United Kingdom, it can be seen that land falls to 2100 permanently below the tides.
"If our findings hold true, coastal communities around the world need to prepare for much more difficult times ahead than can currently be expected," the study warns. "Recent work suggests that, even in the US, rising sea levels this century can cause large-scale migration away from unprotected coastlines, redistributing population density throughout the country and putting great pressure on inland areas."
"We have already moved from a world where sea level is stable to one in which it rises and will continue to increase for decades, and indeed hundreds of years," Strauss told CNN.
These rising oceans spell disaster for coastal residents who may be forcibly displaced. Whole Pacific islands can be submerged, creating waves of climate refugees who may have nowhere to go. They are not protected by international law, so industrialized countries are not legally obliged to grant them asylum.
Sea level rise contributes to warmer global temperatures, changing the type of crops farmers can grow – meaning millions of people can cope with food shortages of drinking water, health crises and disrupted global economy.