“Severe flood” in Boston a harbinger of rising sea levels

“What we have here is a kind of glimpse into the future of Boston,” said Rebecca Shoer, senior program manager of a climate adaptation research group called Stone Living Lab, in an interview with a curious crowd taking photos on the quay.

Friday afternoon's tide was at least 2 feet higher than the typical tide in Boston. Although this was by no means a record high, and would be more likely to occur during a storm, minor flooding did occur.

At the Chart House, the restaurant in John Hancock's old counting house, a few stalwart diners enjoyed a beer on the patio while water sloshed around their feet. Others were stopped because they didn't want to get their shoes wet entering a restaurant (“It's not worth it,” said one man as he and his wife turned back to reach higher ground).

Behind the restaurant, cars navigated around the water that crept from the dock into the streets.

Local scientists and climate activists have dubbed this week's phenomenon a “massive flood,” partly to distinguish it from the better-known “king tides” that typically occur during full and new moons. (There is no scientific definition for a “king tide”).

“Very high” tides are even higher. Technically called perigean spring tides, they occur when there is a new or full moon and the moon is very close to Earth at the same time. At the same time, Shoer explained, the remnants of a tropical storm provide additional wind, pushing the water even higher.

This week's extreme floods are a glimpse into the future. Scientists predict that these sea levels could be comparable to everyday floods in the coming decades due to climate change.

In Boston, sea levels will most likely rise by about a foot by 2050 compared to 2000, climate scientists have found, and another foot could be added in the decades after that.

At the edge of Long Wharf, 31-year-old Krystle Hernandez snapped a photo of the rising tide. She was visiting the city from San Antonio and said that seeing how high the water was rising in Boston — due in part to rising sea levels — reminded her of the melting glaciers in Montana's Glacier National Park last year.

“I wonder what the future will look like,” Hernandez said. “How long will this be around? … You have to see things before you can't see them anymore.”

Perigean spring tides occur about eight times a year, but the planets are only “one piece of the puzzle” of very high water levels, says Greg Dusek, an oceanographer with the National Oceanic and Atmospheric Administration. Seasonal trends can also bring higher tides; high water temperatures in late summer and early fall, for example, cause water molecules to expand.

“That’s when the highest sea temperatures occur (on the east coast),” Dusek said.

This means that a spring tide in September results in higher tides than a spring tide.

Location also plays a role. Boston has a very large tidal range, meaning fluctuating tides are easy to notice here compared to the Gulf Coast of Florida, for example, Dusek said.

“In places with larger tidal ranges, this cycle also tends to be more affected because the tides have a much greater influence on water level fluctuations near the coast,” Dusek said.

Sea level is not a static number. It can fluctuate over months or years depending on water temperature, wind strength, lunar cycles, and more. However, scientists have found that the long-term trend of sea level rise in modern times is primarily caused by climate change. Glaciers and sea ice are melting and ocean temperatures are rising, causing the water to expand.

According to data from a tide gauge in Fort Point Channel, the average sea level in Boston is now more than a foot higher than it was in the 1920s, making the last decade the period with the highest sea levels in Boston since modern weather records began.

In New England, sea level rise is trending faster than the world average, partly because the land along the coast is slowly subsiding due to the effects of ancient glaciers.

Sea level rise projections for Boston after mid-century vary depending on whether humans release fewer planet-warming greenhouse gases into the atmosphere. But even conservative estimates suggest sea level rise of about 2 feet (60 centimeters) over the next 50 years, according to a 2022 report on the impacts of climate change on Boston.

Perhaps even more worrying is the pace at which this rise is occurring: between 2001 and 2019, sea levels rose twice as fast as in the last century.

Towards the end of this decade, a 19-year natural lunar cycle begins, increasing Boston's tidal range and further increasing the risk of flooding.

According to NOAA, another perigee spring tide is expected in mid-October, likely raising water levels in Boston to 12 feet.

Erin Douglas can be reached at [email protected]. Follow her @erinmdouglas23.