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 reported Monday.

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 added that in the absence of human emissions, the ocean surface would be rising less rapidly and might even be falling.

The increasingly routine tidal flooding is making life miserable in places like Miami Beach; Charleston, S.C.; and Norfolk, Va., even on sunny days.

Though these types of floods often produce only a foot or two of standing saltwater, they are straining life in many towns by killing lawns and trees, blocking neighborhood streets and clogging storm drains, polluting supplies of freshwater and sometimes stranding entire 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.

“I think we need a new way to think about most coastal flooding,” said Benjamin H. Strauss, the 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 that 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, because of the warming that scientists have said is almost certainly caused by human emissions.

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 three or four feet by 2100.

Experts say the situation would then grow far worse in the 22nd century and beyond, likely requiring the abandonment of many coastal cities.

The findings are yet another indication that the stable climate in which human civilization has flourished for thousands of years, 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 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, published online Monday by an American journal, Proceedings of the National Academy of Sciences.

In a report issued to accompany that scientific paper, a climate research and communications organization in Princeton, N.J., Climate Central, used the new findings to calculate that roughly three-quarters of the tidal flood days now occurring in towns along the East Coast would not be happening in the absence of the rise in the sea level caused by human emissions.

The lead author of that report, Dr. Strauss, said the same was likely true on a global scale, in any coastal community that has had an increase of saltwater flooding in recent decades.

The rise in the sea level contributes only in a limited degree to the huge, disastrous storm surges accompanying hurricanes like Katrina and Sandy. Proportionally, it has a bigger effect on the nuisance floods that can accompany what are known as king tides.

The change in frequency of those tides is striking. For instance, in the decade from 1955 to 1964 at Annapolis, Md., an instrument called a tide gauge measured 32 days of flooding; in the decade from 2005 to 2014, that jumped to 394 days.

Flood days in Charleston jumped from 34 in the earlier decade to 219 in the more recent, and in Key West, Fla., the figure jumped from no flood days in the earlier decade to 32 in the more recent.