Threat of rising seas to Asian megacities could be way worse than we thought, study warns

By Tara Subramaniam, CNN

Parts of Asia’s largest cities could be under water by 2100 thanks to rising sea levels, according to a new study that combines both the impact of climate change with natural oceanic fluctuations.

Sea levels have already been on the rise due to increasing ocean temperatures and unprecedented levels of ice melting caused by climate change.

But a report published in the journal Nature Climate Change offers fresh insight and stark warnings about how bad the impact could be for millions of people.

While many shoreline Asian megacities were already at risk of flooding, the study suggests that previous analysis underestimated the degree of sea level rise and subsequent flooding caused by natural ocean fluctuations.

Since natural fluctuations have a high degree of variability, their impact is hard to quantify. But the study showed that with the maximum possible impact from natural fluctuations combined with the expected consequences of climate change, several Southeast Asian megacities would become new hotspots of high sea-level rise.

In the Philippine capital Manila, for example, the study predicts that coastal flooding events within the next century will occur 18 times more often than before, solely because of climate change.

But factoring in naturally-occurring fluctuations in sea level increases the frequency of coastal flooding up to 96 times more often than before, the study found.

Millions should ‘prepare for the worst’

Lourdes Tibig, a climate science adviser for the Institute for Climate and Sustainable Cities in the Philippines, said the study’s findings underscore the urgency of addressing climate change.

“The world needs to act on climate change with far more urgency and ambition to protect the millions living in our coastal megacities,” Tibig said.

Manila, where more than 13 million people live, is far from alone.

The study, conducted by scientists at the French National Center for Scientific Research (CNRS), the University of La Rochelle in France and the National Center for Atmospheric Research in the United States (NCAR), found that Thailand’s capital Bangkok, Vietnam’s Ho Chi Minh City and Yangon, Myanmar are particularly at risk, along with Chennai and Kolkata in India, some western tropical Pacific islands and the western Indian Ocean.

The rise in sea level along the west coasts of the United States and Australia would also increase, the study suggested.

Across the Asian megacities alone, more than 50 million people could be affected by the higher than expected rise in sea levels — nearly 30 million of them in India.

Bangkok is home to at least 11 million people, Ho Chi Minh City more than 9 million and Yangon around 5.6 million.

The sea level changes detailed in the report are not likely to take effect until the end of the 21st century. However, if the pace of greenhouse gas emissions increases, the threat becomes more imminent, the authors warned.

NCAR scientist Aixue Hu, one of the study’s authors, said policy makers and the general public alike should be concerned about these potential threats.

“From a policy perspective, we have to prepare for the worst,” Hu said.

Warming waters

According to a NCAR news release, the study found that naturally occurring events such as El Niño, a weather phenomenon known to leave much of the West Pacific, Australia and Asia warmer than usual, could amplify the anticipated sea level rise due to climate change by 20-30%, which also increases the risk of extreme flooding events.

Climate change has already triggered unprecedented extreme flooding in the Asia-Pacific region within the last year.

An analysis by the European Union’s Copernicus Climate Change Service described 2022 as “a year of climate extremes,” including deadly floods in Pakistan and widespread flooding in Australia.

At the same time, ocean temperatures are the highest they’ve ever been and expected to continue increasing.

A January report from the National Oceanic and Atmospheric Administration noted that ocean temperatures were at a record high last year, surpassing the previous record set in 2021.

The past four years have been the warmest four on record for the planet’s oceans.

“And unfortunately, we’re predicting that 2023 will actually be warmer than 2022,” Gavin Schmidt, a climate scientist at NASA, said in January.

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