Sea-level rise could put 300 million people at risk by 2050

NEW DELHI: Rising sea levels and coastal flooding linked to climate change induced warming of waters, melting Arctic sea ice and early onset Antarctic sea ice instability will put hundreds of millions of people more than previously estimated at risk submerging substantial areas of coastal cities such as Mumbai.

The new study by Scott A Kulp and Benjamin H Strauss of the New Jersey-based non-profit Climate Central published in Nature Communications on Tuesday shows that reliance on satellite images has led scientists to underestimate the extent of coastal areas and populations that are at risk of coastal flooding.


The study estimates that by 2050, without dramatic reductions in greenhouse gas emissions, at least 300 million people across the world, that is more than three times the currently accepted number of 80 million, will be at risk of annual coastal flooding.

The largest concentration of at risk population is six Asian countries—China, Bangladesh, India, Vietnam, Indonesia and Thailand—where approximately 237 million live in coastal areas. This is roughly 183 million more than previous assessment of at-risk population in these countries. The number of people at the risk of annual coastal flooding threats by 2050 increased by seven fold, estimated to be about 36 million people up from the previous estimate of 5 million. The numbers at risk of an annual flood by 2050 increased more than eightfold in Bangladesh, twelvefold in Thailand and threefold in China.

This dramatic upward revision in the number of at-risk population is the result of a correction in the way the coastal elevation is determined. “For all of the critical research that’s been done on climate change and sea level projections, it turns out that for most of the global coast we didn’t know the height of the ground beneath our feet,” said Benjamin Strauss, chief scientist and CEO of Climate Central and co-author of the study.

Studies on the impact of rising sea level have so far relied on satellite readings, essentially three-dimensional image of the earth. Satellite readings typically measure elevations of surfaces that are closest to the sky, so in areas where visual access to the ground is blocked it would measure treetops and roof tops. As a result in many areas, particularly highly urbanised areas and those with considerably dense vegetation, the ground level elevation from the sea level was over-estimated. The study puts this over-estimation at more than 2 metres on an average, and up to 4 metres in high density urban areas. What this means is that many areas and populations that were previously thought to be relatively safe from the impacts of coastal floods and rise in sea levels are in fact at risk.

The new research corrects for this overestimation by using artificial intelligence for a more sophisticated assessment of the topography of the coastline. “Our data improve the picture, but there is still a great need for governments and aerospace companies to produce and release more accurate elevation data. Lives and livelihoods depend on it,” said Strauss.

The study by Kulp and Strauss reaffirms the findings of the special report on oceans by the United Nations’ climate science body, the Intergovernmental Panel on Climate Change (IPCC) that was released in September. Anjal Prakash, the co-ordinating lead author of the IPCC’s Special Report on the Ocean and Cryosphere, said that the new information provided in the study is “about the number of people vulnerable to the rise in sea level.”

The IPCC special report on oceans and the cryosphere concluded that extreme sea-level events, such as surges from tropical cyclones, that are currently historically rare will become common by 2100 under all emissions scenarios due to increasing global mean sea level rise, and that under all future emissions scenarios, many low-lying megacities and small islands at almost all latitudes will experience such events annually by 2050.

This new study augments the understanding of the scale of the impact of rising sea levels. “These assessments show the potential of climate change to reshape cities, economies, coastlines, and entire global regions within our lifetimes,” said Scott Kulp, a senior scientist at Climate Central and lead author of the study.

Prakash said that “as the science advances, we would be getting newer and more nuanced information. The information will have to lead us to knowledge and decision making, followed up by better planning and implementation.”

For scientists, this study is yet another indication of the need to alter the way climate change is addressed by policy makers and implementers. “We need to clearly move away from treating climate change-related events as disaster management,” said Prakash. Disaster management, he explained, is seen as something that may occur once or more in a year. “If you see the recent data, you would find that more extreme events are being reported and frequency of these events has increased considerably over past 4-5 years. This is the new normal and so we may like to plan it accordingly.”

“As the tideline rises higher than the ground people call home, nations will increasingly confront questions about whether, how much, and how long coastal defences can protect them,” said Kulp.