By the middle of the century, sea levels in Boston and elsewhere in the Northeast are likely to be about 16 inches higher than they were in 2000 — a much more significant increase than over the previous century, according to a new federal report.
The report also found that the region will likely experience significantly higher tides and so-called sunny-day flooding than much of the rest of the US coastline, imperiling more coastal homes, roads, and drinking water and sewer systems.
In a worst-case scenario, the government reported sea levels in the Northeast could rise as much as 21 inches by 2050. By comparison, over the past century, sea levels in the region have risen by nearly one foot.
“This new data on sea rise is the latest reconfirmation that our climate crisis — as the president has said — is blinking ‘code red,’ ” Gina McCarthy, national climate adviser to President Biden, said in a statement. “We must redouble our efforts to cut the greenhouse gases that cause climate change while, at the same time, help our coastal communities become more resilient.”
The report by the National Oceanic and Atmospheric Administration is the first time the US government has made specific predictions about rising sea levels by 2050. Based on tide gauges, satellite observations, and computer models, it projects that, on average, the coastal waters of the United States will rise between 10 and 12 inches by 2050.
It gets even grimmer in later years, as seas are likely to rise at an accelerating rate.
By 2100, the scientists estimate, coastal waters off the Northeast could rise between 2 feet and 7 feet, and keep going, to as high as 12 feet by 2150.
Those later estimates depend much more on how much fossil fuels continue to be used, and how quickly the ice sheets covering Antarctica and Greenland melt. There’s little that can be done to change the amount that tides will rise over the coming three decades, given the vast quantity of greenhouse gases that have already been pumped into the atmosphere, according to the report.
“Clearly, we need to begin planning for the challenges this will pose for Boston now,” said Rob DeConto, a climate scientist at the University of Massachusetts Amherst, who studies rising sea levels. “After 2050, our greenhouse gas emissions will make all the difference in the world.”
Without rapid cuts in emissions, DeConto noted, the planet is likely to look very different in the next century.
After 2100, seas could begin rising by one inch a year, up from roughly one every eight years now, he said.
“Those sorts of rates of sea level rise would be beyond our capacity to protect parts of the city, and some areas of Boston and the Massachusetts coastline would have to be abandoned,” DeConto said.
The report also found that rising seas over the coming years will increase the frequency of coastal flooding, even in the absence of storms or heavy rainfall.
Nationally, such sunny day flooding in 2050 is likely to occur more than 10 times as often as it does today, NOAA said.
“These numbers mean a change from a single [flooding] event every 2-5 years to multiple events each year, in some places,” said Nicole LeBoeuf, NOAA’s national ocean service director.
In Boston, flooding is likely to be considerably worse than elsewhere. A previous NOAA report found that the city has had more high-tide flooding than nearly any other coastal community in the country.
In 2020, Boston had 11 days of such flooding, more than twice the number in 2000. In a decade, NOAA scientists have projected, there could be as many as 35 days of such flooding, and up to 95 days a year by 2050.
Boston officials said they recognize the threat and are developing plans to protect city neighborhoods from up to 40 inches of sea-level rise.
Last year, after pressure from environmental advocates, city officials for the first time began requiring developers in designated flood-prone areas, such as the Seaport, to build properties that could withstand such sea level rise.
“Each new report reiterates what we already know: Climate change is here and demands urgent action,” said the Rev. Mariama White-Hammond, the city’s environment chief. “Right now, we have an opportunity to address the threats that climate change presents, while simultaneously creating a more equitable and just society.”
The NOAA report adds to a body of data showing the effects of rising sea levels on the Northeast. Its data is similar to the most recent report on the subject produced by the United Nations Intergovernmental Panel on Climate Change, which estimated that the region’s coastal waters would rise between 12 and 15 inches by 2050.
In 2016, DeConto’s team at UMass-Amherst found that the accelerating melting of Antarctica’s ice would disproportionately hit East Coast cities.
As ice melts on the South Pole, the resulting gravitational pull on the ocean, as well as the gradual sinking of land in the Northeast, means that Boston and the surrounding region are likely to experience about a 25 percent higher rise in sea levels than other parts of the planet.
Around the same time, the Boston Green Ribbon Commission estimated, the city would experience between 7 inches and 18 inches of rising sea level by 2050.
“The NOAA report is an opportunity to refresh the urgency of what we already know, and ask ourselves whether we are moving fast enough to meet the threat to people, neighborhoods, and the economy in Boston,” said Amy Longsworth, executive director of the Green Ribbon Commission.
The threat of flooding from major storms and rising sea levels already poses a dire threat to Massachusetts.
Already, at current sea levels, the state has an estimated 162,798 residential properties, 12,918 miles of roads, 14,644 commercial properties, and nearly 2,500 other critical buildings, such as hospitals, power stations, and government offices, that are at risk of being deluged and becoming inoperable, according to a report last year by First Street Foundation, a New York nonprofit research group that specializes in flood risk.
By 2051, an additional 27,714 residential properties, 1,181 miles of roads, 2,119 commercial properties, and more than 450 critical buildings will face similar risks, that report projected.
NOAA’s latest findings worry some that it presages more dour reports in the future, as computer models become more advanced and the government launches more sophisticated satellites to monitor climate change.
“What today’s report reinforces is that what looked like a worst-case scenario before is now more likely to occur, and the conservative estimates were perhaps too low,” said Alice Brown, chief of planning and policy at Boston Harbor Now. “Changing projections mean that higher standards are going to be needed.”
David Abel can be reached at email@example.com. Follow him on Twitter @davabel.