Sea levels along the United States coast will rise about a foot or more on average by 2050, government scientists said on Tuesday, with the result that rising waters now seen as a ” harmful flood” will become much more damaging.

A report by researchers from the National Oceanic and Atmospheric Administration and other agencies also found that at the current rate of warming, at least two feet of sea level rise is expected by the end of the century.

“What we are reporting is historic,” NOAA Administrator Rick Spinrad said at a press conference announcing the results. “The United States is expected to experience as much sea level rise over the next 30 years as we have seen over the past century.”

Dr Spinrad said that while reducing greenhouse gas emissions to limit warming was of crucial importance, the projected sea level rise by 2050 “will happen, whatever we do in emissions”.

The report is an update of a 2017 study and is also based on data from tide gauges and satellite observations.

Corn the new study has relatively accurate estimates of sea level rise by 2050, the result of improved computer modeling and a better understanding of the impact of global warming on the huge ice sheets of Greenland and the United States. ‘Antarctic. This “provides more confidence in our ability to predict” effects by mid-century, said William Sweet, an oceanographer with NOAA’s National Ocean Service and author of the report.

About 40% of the US population, or 130 million people, live within 60 miles of the ocean. But sea level rise will not affect them all equally, as it is not uniform.

In the United States, land subsidence and sediment compaction along much of the eastern and Gulf coasts are adding to the increase; in these regions, sea level rise could exceed one foot in the next three decades, the report said.

On the west coast, land subsidence and compaction are less common, so sea level rise is expected to be at the lower end of the projections.

The report says the calculated increase over the next three decades means tidal and storm surge related flooding will be higher and reach further inland, increasing the damage.

What the report describes as moderate or generally damaging flooding will occur 10 times more often by 2050 than today. Major destructive coastal flooding, while still relatively rare, will also become more frequent.

For communities on the east and gulf coasts, the expected rise in sea level “will create a sharp increase in the frequency of coastal flooding, even in the absence of storms or heavy rains,” said Nicole LeBoeuf, director. of the National Ocean Service.

Currently, many communities on these coasts regularly experience “harmful” or “sunshine” flooding, when high tides become even higher due to the influence of the moon, wind, or other factors.

But what was once harmful flooding is likely to turn damaging, Dr Sweet said.

“We definitely anticipate a change in flood regime,” he said.

The report projects that sea level will rise an average of 10 to 12 inches by 2050, which is about as much as the rise over the 100 years from 1920 to 2020. These projections do not change, regardless of regardless of the amount of greenhouse gas emissions reduced. during this period.

Estimates of sea level rise by 2100 in the report are less certain. But in this case, the global trajectory of emissions will have a significant effect. Letting emissions continue unabated could add another 1.5 to 5 feet to sea level by the end of the century, for a total of up to 7 feet, the report concludes.

The report provides detailed sea level projections for states and territories by decade for the next 100 years. Dr Spinrad said it was intended to help local officials, planners and engineers make decisions about where or how to protect critical infrastructure such as roads, sewage treatment systems and power stations, and to adapt differently to rising sea levels.

He described the report as a “wake-up call” for the United States. “But it’s a red flag that comes with a silver lining,” he said. “It provides us with the information we need to act now to best position ourselves for the future.”