By Tim Radford
LONDON, 3 September, 2019 − What are now considered once-in-a-hundred-years floods are on the increase in the US. Later this century, they could happen to northern coastal states every year.
And even in the more fortunate cities along the south-east Atlantic and the Gulf of Mexico coasts, the once-in-a-century floods will happen a lot more often: somewhere between every 30 years and every year.
In a second study, a team of distinguished scientists argues that the US should face the inevitable and begin to plan for a managed, strategic retreat from its own coasts.
At the heart of both studies is a set of new realities imposed by a rapidly-heating ocean and higher air temperatures worldwide. As the icecaps of Greenland and Antarctica melt, and as the glaciers of Canada and Alaska retreat, so sea levels have begun to rise inexorably.
But as the oceans increase in average temperature, thanks to an ever-warmer atmosphere driven by greenhouse gases from profligate combustion of fossil fuels, so the oceans have begun to expand: warmer waters are less dense, and thus higher.
“We need to stop picturing our relationship with nature as a war. We’re not winning or losing, we’re adjusting to changes in nature”
And there is a third factor. With warmer seas there will be more frequent and more violent hurricanes and windstorms, more damaging storm surges and yet more torrential rainfall.
Researchers from Princeton University report in the journal Nature Communications that they considered all three factors to create a flood hazard map of the US. Simply because of rising waters, New England states can expect to see what were once rare events almost every year.
“For the Gulf of Mexico, we found the effect of storm surge is compatible with or more significant than the effect of sea level rise for 40% of counties,” said Ning Lin, a Princeton engineer.
“So if we neglect the effects of storm climatology change, we would significantly underestimate the impact of climate change for these regions.”
Growing Atlantic danger
Exercises of this kind are about planning for the worst: were the Princeton research the only such study, city chiefs could afford to relax. But it is not.
For years climate scientists and oceanographers have been warning of ever-greater hazard to Atlantic America. They have warned of ever more torrential rains and the hazards of ever more damaging floods even in disparate cities such as Charleston and Seattle; they have even warned of high tide floods on a daily basis in some cities, and they have proposed that an estimated 13 million Americans could become climate refugees, driven by the advancing seas from their own homes.
All of which is why a trio of researchers argue for the need to accept the inevitable and step back from the sea, and they say so in the journal Science. They argue that the US should start to prepare for retreat by limiting development in the areas most at risk.
“Fighting the ocean is a losing battle,” said A R Siders of Harvard and the University of Delaware. “The only way to win against water is not to fight. We need to stop picturing our relationship with nature as a war. We’re not winning or losing, we’re adjusting to changes in nature.”