Updated Feb 16, 2022 - Energy & Environment

U.S. sea levels to rise by a foot through 2050, causing "profound" flooding

Picture of flooding in coastal Maryland.

A man rides a bicycle through flood waters in downtown Annapolis, Md., on Oct. 29, 2021. Photo: Jim Watson/AFP via Getty Images

The U.S. is poised to see as much of a rise in sea levels through the year 2050 as it has experienced in the past century, with additional increases through 2150, according to a comprehensive new federal report out Tuesday.

Why it matters: Sea-level rise is one of the most tangible present-day effects from human-caused climate change that is being felt in the U.S., with coastal flood events becoming far more common and damaging in just the past few decades.

Driving the news: The National Oceanic and Atmospheric Administration (NOAA) released the report along with about six other federal agencies that play a role in tracking the rise in sea level.

  • It updates figures from 2017 by taking into account the newest sea level rise projections, and breaks trends down into different time periods. Data from tide gauges, satellite instruments and the latest computer models are all incorporated.
  • The report includes extreme water level probabilities for points along the U.S. coastline, and will be incorporated into the next National Climate Assessment, which is underway.
  • The assessment projects an additional 10- to 12-inch increase in sea levels by 2050, with higher amounts in some parts of the country due to changes in land height and ocean currents.
  • The East and Gulf coasts are expected to see a greater rise in sea level than the West Coast, for example.

The big picture: The range of sea level rise at the global, national and regional levels has narrowed since 2017, thanks to improved measurements, a better understanding of polar ice sheets and refinements of computer modeling.

  • The report projects the sea level rise along the contiguous U.S. coastline to be between 1 and 7 feet in 2100, compared to 2000 levels, and 2.6 to 13 feet by 2150.
  • The range in these projections largely depends on the amount of greenhouse gas emissions and resulting warming.

Threat level: The report warns that the sea level rise through 2050 will dramatically escalate the frequency and severity of coastal flooding, including so-called "sunny day" flooding at times of high tide in areas such as Charleston, S.C. and Miami.

  • The report says that nationally, a "flood regime shift" is projected to occur by 2050, with moderate high tide flood frequencies to increase by more than a factor of 10 nationally, along with a five-fold increase in major high tide flood frequencies.
  • It notes that "significant consequences" are in store for coastal infrastructure, absent new efforts to reduce risk exposure.
  • Moderate and typically damaging high tide flooding is projected to increase from an average frequency of 0.3 events per year in 2020, to 4 events per year in 2050, the report finds.
  • And minor or nuisance high tide flooding, currently becoming the norm in parts of Miami and influencing real estate prices, is likely to dramatically increase from about three events per year as a national average in 2020 to more than 10 events per year.
  • "The minor nuisance-like flooding that's becoming a growing problem in many East and Gulf Coast communities, some West Coast, is likely to become damaging flooding," said NOAA oceanographer William Sweet during a press conference call. "That extra foot on average or so around the country is just going to reach further inland and grow deeper and more severe."

What they're saying: Ben Strauss, CEO and chief scientist of the research group Climate Central, said, "Just one foot of sea level rise will change a lot of American lives."

  • "Nationwide, about a million Americans live on land less than one yardstick above the high tide line. That jumps to five million below two yardsticks — the size of Houston plus Chicago, averaging almost 70,000 people per vertical inch," he said via email.
  • "Our national sea level threat has started slowly, but it's going to accelerate like a rocket," Strauss added.
  • Jeremy Porter, chief research officer at the nonprofit First Street Foundation, said the findings "amplify concerns" raised in his work about the non-linear growth in sea level rise and flood risk.
  • "The simple addition of a few inches of sea level rise exponentially increases the consequences of coastal surge events," he said in an email. 

Of note: The most extreme sea level rise scenario from NOAA's 2017 report, which showed an increase of 8 feet of global mean sea level rise by 2100, is no longer considered plausible, the new analysis shows.

Editor's note: This story has been updated with Ben Strauss and Jeremy Porter's comments.

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