NEW YORK • The worsening of tidal flooding in American coastal communities is largely a consequence of greenhouse gases from human activity, and the problem will grow far worse in coming decades, scientists have reported.
Those emissions, primarily from the burning of fossil fuels, are causing the ocean to rise at the fastest rate since at least the founding of ancient Rome, the scientists said.
They also confirmed previous forecasts that if emissions were to continue at a high rate over the next few decades, the ocean could rise as much as 1m by 2100.
"I think we need a new way to think about most coastal flooding," said Dr Benjamin Strauss, primary author of one of two related studies released on Monday. "It's not the tide. It's not the wind. It's us. That's true for most of the coastal floods we now experience."
In the second study, scientists reconstructed the level of the sea over time and confirmed it is most likely rising faster than at any point in 28 centuries, with the rate of increase growing sharply over the past century - largely, they found, due to the warming scientists have said is almost certainly caused by human emissions that have raised global temperatures by about 1 deg C since the 19th century.
The increasingly routine tidal flooding is making life miserable in places like Miami, Florida; Charleston, South Carolina; and Norfolk, Virginia, even on sunny days.
Though these types of floods often produce only 30cm to 60cm of standing saltwater, they are killing lawns and trees, blocking streets, polluting supplies of freshwater and stranding island communities for hours by overtopping the roads that tie them to the mainland.
Such events are just an early harbinger of the coming damage, the new research suggests. Experts say the situation will grow far worse in the 22nd century and beyond, likely requiring the abandonment of many coastal cities.
In a report issued to accompany one of the scientific papers, climate research and communications organisation Climate Central used the new findings to calculate that roughly three-quarters of the tidal flood days now occurring in towns along the United States east coast would not be happening in the absence of the rise in the sea level caused by human emissions.
Dr Strauss, the report's lead author, said the same was likely true on a global scale, in any coastal city that has had an increase of saltwater flooding in recent decades.
The findings are another indication that the stable climate in which human civilisation has flourished, with a largely predictable ocean permitting the growth of great coastal cities, is coming to an end.
"I think we can definitely be confident that sea-level rise is going to continue to accelerate if there's further warming, which inevitably there will be," said Dr Stefan Rahmstorf, a professor of ocean physics at the Potsdam Institute for Climate Impact Research in Germany, and co-author of one of the papers that was published online on Monday by an American journal, Proceedings of the National Academy of Sciences.
Dr Rahmstorf said the rise would eventually reach 1.5m and far more - the only question was how long it would take. Scientists say the recent climate agreement negotiated in Paris is not remotely ambitious enough to forestall a significant melting of Greenland and Antarctica, although, if fully implemented, it may slow the pace somewhat.
"Ice simply melts faster when the temperatures get higher," Dr Rahmstorf said.
NEW YORK TIMES