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A major new report released early Monday morning contained dire projections for the warming planet and revealed that humans are contributing to changes to the climate at an “unprecedented” pace.

The report, by the United Nations’ Intergovernmental Panel on Climate Change found that the world has already warmed roughly 1.1 degrees Celsius since the 19th century, already approaching the 1.5 degree level, at which the Paris Climate Agreement seeks to limit warming.

The report warns that the window to address the averse effects of climate change is narrowing, leaving open the question about what can be done to blunt the worst effects of human activity on the planet.

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One measure of a warming planet and climate change is rising sea levels. As oceans warm because overall global temperatures are rising, seawater expands and causes water levels to rise, according to the NOAA. Sea levels also rise when land-based ice, like glaciers and ice sheets, melts, adding water to the ocean.

Massachusetts’ coastal towns are increasingly grappling with this issue. The number of flooding days in the state is set to increase, according to projections from the National Oceanic and Atmospheric Administration, as damaging floods that used to occur only during storms are now happening more regularly.

And sea level rise is already happening across the globe and in Massachusetts. The sea level off the coast of Massachusetts is 8 inches higher than it was in 1950, and it has significantly accelerated in recent years, now rising about 1 inch every eight years, according to the NOAA.

Ian Sue Wing, a professor at Boston University’s Department of Earth and Environment, said the world will most likely reach an average sea level rise of roughly one and a half feet under a high-emissions, high-warming scenario by the 2060s to 2080s, and, citing a 2019 IPCC report, the situation could become even more dire for the North Atlantic Coast in later decades.

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“More worrying, models have long shown that even though we might make decisions on time-frames of a century, nature operates on much longer scales,” Wing wrote in an e-mail. “Warming, ocean absorption of heat, and rising sea levels will continue for hundreds of years and that these will be associated with loss of polar ice sheets, further adding to ocean water volumes, and sea heights. I can’t speculate on what Boston might look like so far into the future ... but it’s cause for concern.”

How it could play out in Boston

In Boston, where approximately 17 percent of the city was built on landfill that was once tidal flats, marshes, or water — the area is incredibly vulnerable to flooding and rising sea levels.

According to simulations by the NOAA, even one foot of sea-level rise means flooding in dense areas of Boston, including the Back Bay area and specifically the area surrounding the Prudential Center. Parts of the Mass. Pike in the Back Bay could become a flood-prone area, disrupting traffic flow.

In the maps below, areas that are connected to the ocean are shown in shades of blue. The darker the color, the greater the depth of water in that area. Low-lying areas, displayed in green, are hydrologically “unconnected” areas that may also flood. Flooding in these areas is determined by elevation as well as the area’s drainage.

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In an extreme worst-case scenario, which NOAA calls highly unlikely, global sea levels could rise by as much as 8.2 feet by 2100. As the map shows, such sea level rise would inundate whole swaths of downtown Boston at high tide including the Back Bay, Fenway, the South End, the Seaport District, much of East Boston, and parts of Dorchester.

Simulated sea level rise in the Boston area.
Simulated sea level rise in the Boston area.National Oceanic and Atmospheric Administration

Parts of the city including Faneuil Hall and TD Garden would be completely flooded.

In Boston, sea level is forecasted to rise to nearly 16 inches by 2050, according to the NOAA. Experts believe that if immediate action were taken to fight climate change, the global sea level would still likely rise at least 1 foot by 2100.

North of the city

In addition to Boston, coastal communities like Revere and Quincy face threats from rising sea levels, including flooding, erosion, and storm hazards.

Rising sea levels are also impacting coastal communities like Revere because they erode wetlands and beaches. Wetlands, like those found in Revere’s Rumney Marsh Reservation, are vulnerable because of their low elevations. They provide habitats for birds and fish, and losing coastal wetlands would harm ecosystems and remove an important line of defense against coastal flooding.

According to the Environmental Protection Agency, about one-third of New England’s coastal wetlands have been destroyed due to human activity.

Some low-lying areas of Revere are currently vulnerable to flooding, according to the NOAA’s measurement of water height, particularly near Wonderland Greyhound Park, Diamond Creek, and Oak Island Park.

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But as sea levels rise, water begins encroaching beyond Revere Beach, and the city’s marshes would become flooded. According to the simulation, the water spreads further inland, submerging some residential parts of the city.

Simulated sea level rise in Revere.
Simulated sea level rise in Revere.National Oceanic and Atmospheric Administration

South of the city

According to the NOAA’s projections, low-lying areas in Quincy at risk for floods become more widespread with rising sea levels. The NOAA’s water height measurement shows that some areas of the city are already prone to flooding, particularly in the marshes of Blacks Creek. A stretch along Wollaston Beach, Faxon Field, and parts of the Presidents Golf Course are also vulnerable.

As the sea level rises, the impacts are visible along Quincy’s Neponset River and in the areas surrounding Rock Island, Blacks Creek, and Wollaston Beach.

Simulated sea level rise in Quincy.
Simulated sea level rise in Quincy.National Oceanic and Atmospheric Administration

Sea level rise also impacts the infrastructure in Massachusetts’ coastal communities.

A recent study found that rising seas post a threat to the Massachusetts Bay Transportation Authority’s rail network over the next 50 years, with the potential to inundate vast portions of the system and sever crucial links. The report’s authors warned that the system must take sweeping action to fortify its coastal infrastructure against the realities of a warming planet.

As sea levels rise and flooding increases, Massachusetts homes will also face increasing risk of damage. A report found that in Boston, where more than 3,000 properties a year will face substantial risk of damage from flooding, those losses are likely to exceed $62 million a year in 30 years, 75 percent more than now.

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Amanda Kaufman can be reached at amanda.kaufman@globe.com. Follow her on Twitter @amandakauf1. Maria Elena Little Endara can be reached at mariaelena.littleendara@globe.com.