Even if humanity beats the odds and caps global warming at 1.5 degrees Celsius above pre-industrial levels, seas will rise for centuries and overwhelm the cities that are currently home to half a billion people, have warned. Tuesday researchers.
In a world that still heats up half a degree above that benchmark, an additional 200 million urban dwellers today would regularly find themselves knee-deep in seawater and more vulnerable to devastating storm surges, said. they reported in Environmental research letters.
In all scenarios, the hardest hit will be Asia, which has nine of the ten most at-risk megacities.
The land that is home to more than half of the populations of Bangladesh and Vietnam would fall below the high tide line in the long run, even in a 2 ° C world. Built-up areas in China, India and Indonesia would also face devastation.
Most projections for sea level rise and the threat it poses to coastal cities go through the turn of the century and range from half a meter to less than double, depending on how quickly carbon pollution is reduced.
Corn the oceans will continue to swell for hundreds of years beyond 2100 – fueled by melting ice caps, trapped heat in the ocean, and the dynamics of warming water – regardless of how intensely the gas emissions to greenhouse effect are reduced, the results show.
Not “if” but “when”
“About 5 percent of the world’s population today lives on land below the level where the high tide level is expected to rise due to the carbon dioxide human activity has already added to the atmosphere,” he said. said lead author Ben Strauss, CEO and chief scientist of Central Climate, told AFP.
The current concentration of CO2 – which persists for hundreds of years – is 50% higher than in 1800, and the average temperature at the Earth’s surface has already risen by 1.1 ° C.
That’s enough to raise sea level by almost 2 meters (over six feet), whether it takes two centuries or 10, Strauss said.
The 1.5 ° C warming limit enshrined in the Paris Agreement that nations will try to keep in play in the COP26 Climate Summit in Glasgow next month translates to almost 3 meters in the long run.
Unless engineers figure out how to quickly remove massive amounts of CO2 of the atmosphere, this amount of sea level rise is not a matter of “if” but “when,” the study said.
These are the optimistic scenarios.
“The main conclusion for me is the stark difference between a world of 1.5 ° C after a big reduction in pollution and a world after 3 ° C or 4 ° C of warming,” Strauss said.
“In Glasgow and for the rest of this decade, we are fortunate to help or betray a hundred generations to come.”
National commitments to reduce carbon emissions under the 2015 Paris Treaty would, if honored, see the Earth warm by 2.7 ° C by 2100. If efforts to suppress gases greenhouse flicker, temperatures could rise 4 ° C or more above mid-19th century levels.
This warming would increase the world’s oceans by 6 to 9 meters in the long term and force the cities that are currently home to nearly a billion people to either mount massive defenses against future sea level rise or to rebuild themselves on higher grounds.
In China alone, the land occupied today by 200 million people would fall below high tide in a 3 ° C scenario. And the threat isn’t just long-term: Without massive levees, China’s cityscapes that are home to tens of millions of people could become unlivable within 80 years.
“1.5 ° C of warming will always lead to devastating sea level rise, but the warmer alternatives are much worse,” Strauss said.
“We’re in bad shape but it’s never too late to do better, and the difference we could make is huge.”
At higher warming levels, the danger increases dramatically of triggering the irreversible disintegration of the ice caps or the release of natural CO stores.2 and methane in permafrost, scientists warn.
Keeping global warming as low as possible also saves us time to adapt.
“It is almost certain that the seas will rise more slowly in a world that is 1.5 ° C or 2 ° C warmer,” Strauss said.
Researchers from Princeton University and the Potsdam Institute for Climate Impact Research in Germany contributed to the study.