NEW YORK • Rising seas could affect three times more people by 2050 than previously thought, according to new research, threatening to all but erase some of the world's major coastal cities.
The authors of a paper published on Tuesday developed a more accurate way of calculating land elevation based on satellite readings, a standard way of estimating the effects of sea level rise over large areas, and found that the previous numbers were far too optimistic.
The research shows 150 million people are living on land that will be below the high-tide line by mid-century. For example, Southern Vietnam, a major rice-growing area, could all but disappear.
More than 20 million people in Vietnam, almost one quarter of the population, live on land that will be inundated. Much of Ho Chi Minh City would disappear with it, according to the research by Climate Central, a science group based in New Jersey, and published in the journal Nature Communications. The projections do not account for future population growth or land lost to coastal erosion.
Standard elevation measurements using satellites struggle to differentiate the true ground level from the tops of trees or buildings, said Climate Central's researcher Scott Kulp, one of the paper's authors. So he and the group's CEO Benjamin Strauss used artificial intelligence to determine the error rate and correct for it.
In Thailand, more than 10 per cent of citizens live on land that is likely to be inundated by 2050, compared with just 1 per cent according to the earlier technique. Bangkok is particularly imperilled.
Climate change will put pressure on cities in multiple ways, said Bangkok resident Loretta Hieber Girardet, a United Nations disaster risk-reduction official. Even as global warming floods more places, it will also push poor farmers off the land to seek work in cities.
"It is a dire formula," she said.
A global map accompanying the study shows large parts of eastern Sumatra flooded by 2050 as well as Port Klang and parts of Malacca in Malaysia. In Singapore, only small parts of the downtown area, Boon Lay and the southern islands are at risk, the map shows.
In Shanghai, one of Asia's most important economic engines, water threatens to consume the heart of the Chinese city and many other areas around it.
The findings do not have to spell the end of those areas. The new data shows 110 million people already live in places that are below the high-tide line, which Strauss attributes to protective measures like seawalls and other barriers. Cities must invest vastly greater sums in such defences, Mr Strauss said, and they must do it quickly.
But even if that investment happens, defensive measures can go only so far. Mr Strauss offered the example of New Orleans, a city below sea level that was devastated in 2005 when its extensive levees and other protections failed during Hurricane Katrina. "How deep a bowl do we want to live in?" he asked.
The new projections suggest that much of Mumbai, India's financial capital and one of the largest cities in the world, risks being wiped out. Built on what was once a series of islands, the city's historic downtown core is particularly vulnerable.
Overall, the research shows that countries should start preparing now for more citizens to relocate internally, according to Ms Dina Ionesco of the International Organisation for Migration, an intergovernmental group that coordinates action on migrants and development. "We've been trying to ring the alarm bells," she said. "We know that it's coming."
There is little modern precedent for this scale of population movement, Ms Ionesco added.
In other places, the migration caused by rising seas could trigger or exacerbate regional conflicts.
Basra, the second-largest city in Iraq, could be mostly underwater by 2050. If that happens, the effects could be felt well beyond Iraq's borders, according to retired Marine Corps lieutenant-general John Castellaw, who was chief of staff for the US Central Command during the Iraq War.
Further loss of land to rising waters there "threatens to drive further social and political instability in the region, which could reignite armed conflict and increase the likelihood of terrorism", said Mr Castellaw, who is on the advisory board of the Centre for Climate and Security, a research and advocacy group in Washington.
"So this is far more than an environmental problem," he said. "It's a humanitarian, security and possibly military problem, too."
NYTIMES
