Large parts of New York, Shanghai, Mumbai and other cities will slip under the waves even if an upcoming climate summit limits global warming to 2 degrees Celsius, scientists say.
A 2C spike in Earth’s temperature would submerge land currently occupied by 280 million people, according to a study published by US-based research group Climate Central.
An increase of 4C — humanity’s current trajectory — would cover areas lived on by more than 600 million people, the study said.
The study’s lead author, Ben Strauss, said the 2C temperature rise will pose a “long-term, existential danger to many great coastal cities and regions”.
Sea level rises corresponding to these 2C or 4C scenarios could unfold in two hundred years, but would more likely happen over many centuries, perhaps as long as 2,000 years, the study said.
Capping the rise in Earth’s temperatures to 2C above pre-industrial levels is the core goal of the 195-nation UN climate summit in Paris from November 30 to December 11.
The most effective way to slow global warming is to slash the output of the greenhouse gases which drive it.
But even if emissions reduction pledges submitted by 150 nations ahead of the Paris summit are fulfilled, it would still put us on a pathway for a 3C world, the United Nations has warned.
Achieving the two-degree goal remains a serious challenge.
Mr Strauss and colleagues apply on a global scale the same methodology they used for a recent study that focused on temperature-linked sea level rise in the United States, published in the US Proceedings of the National Academy of Sciences.
That study concluded that both Miami and New Orleans are doomed to crippling impacts.
Chinese cities among most vulnerable
In the new report, the country hit hardest by sea level rise under a 4C scenario is China.
Some 145 million people live in Chinese cities and coastal areas that would eventually become ocean were temperatures to climb that high.
Four of the 10 most devastated megacities would be Chinese: land occupied today by 44 million people in Shanghai, Tianjin, Hong Kong and Taizhou would be underwater.
India, Vietnam and Bangladesh do not fare much better. Asia is home to 75 per cent of the populations that today reside in zones that would no longer be classified as land in a climate-altered future.
Thirty-four million people in Japan, 25 million the United States, 20 million in the Philippines, 19 million Egypt and 16 million in Brazil are also in future 4C seascapes.
While the 2C scenario is also grim, limiting warming to that extent would spare China and other nations much misery, Mr Strauss said.
“There is a world of difference between 2C and 4C, which threatens more than double the damage,” he said.
The sea level rise corresponding to 2C would eventually be 4.7 metres, and for 4C almost double that, the study found.
The projections are based on climate models taking into account the expansion of ocean water as it warms, the melting of glaciers, and the decay of both the Greenland and West Antarctic icesheets.
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