A new study estimates that more than 600 million people could face the threat of coastal flooding by the end of the century in a worst-case scenario (1). And the new figures suggest that three times as many people than previously estimated may be at risk due to sea-level rise by mid-century, according to the analysis published on 30 October in Nature Communications.
The authors say that unless greenhouse gas emissions are reduced or sea defences are ramped up, at-risk coastal cities will flood at least once a year by 2050 – placing up to 300 million people at risk.
The researchers Dr Benjamin Strauss and Dr Scott Kulp at Climate Central — an independent organisation in New Jersey, New York that conducts key research on climate change — performed the most elaborate assessment of coastal topographies to date. More specifically, they used artificial intelligence to train a model based on several updated datasets including accurate satellite maps of global altitude.
The findings reveal that more people now live on land below annual flood levels – 250 million versus the 65 million based on older estimates. And by 2100, this number could reach triple if global warming continues unabated. Fooding will potentially become more expensive to deal with – the World Bank previously approximated damages up to $1 trillion per year, however, these figures will need to be updated too.
Asian megacities appear to be most vulnerable to rising sea-levels. Jakarta is a prime example of the increasing risk of flooding. Indeed, the Indonesian government has just announced plans to relocate the sinking capital to another city in Kalimantan (Indonesian Borneo).
In Indonesia alone, 23 million people are at risk, up from the previous estimate of 5 million. But by far the biggest increases in estimates were for China with 87 million by 2050 compared to 26 million and Bangladesh, a dramatic increase from 5 million to 50 million.
Why such large discrepancies?
Older models contained so-called vertical errors. In other words, the models were based on satellite data that overestimated the altitude of land due to the presence of many tall buildings and trees. This time, the authors used artificial intelligence to correct for incorrect data.
The newer models are still likely to contain some amount of vertical error, therefore, these figures should also be treated with a degree of caution, Krauss says. But even more frightening is that they might, in fact, still underestimate future sea rise. The projections take into account moderate emissions cuts in line with targets of the Paris agreement that many countries are not on course to meet.
The silver lining, Strauss told the Guardian is that “although many more people are threatened than we thought, the benefits of action are greater.”
Better planning and coastal improved coastal defences are urgently needed to prevent economic harm and potential loss of life. But coastal defences can only work for so long. The authors hope the new data will spur governments toward more ambitious emissions targets and greater action.
(1) Kulp, S.A. & Strauss, B.H. New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding. Nature Communications (2019). DOI: 10.1038/s41467-019-12808-z