– Officials in the Florida Keys announced what many coastal governments nationwide have long feared but few have been willing to admit: As seas rise and flooding gets worse, not everyone can be saved.

And in some places, it doesn’t even make sense to try.

This month, Rhonda Haag, Monroe County’s sustainability director, released the first results of the county’s yearslong effort to calculate how high its 300 miles of roads must be elevated to stay dry, and at what cost. Those costs were far higher than her team expected — and those numbers, she said, show that some places can’t be protected, at least at a price that taxpayers can be expected to pay.

“I never would have dreamed we would say ‘no,’ ” Haag said in an interview. “But now, with the real estimates coming in, it’s a different story. And it’s not all doable.”

The results focus on a single 3-mile stretch of road at the southern tip of Sugarloaf Key, a small island 15 miles up U.S. Hwy. 1 from Key West. To keep those 3 miles of road dry year-round in 2025 would require raising it by 1.3 feet, at a cost of $75 million, or $25 million per mile. Keeping the road dry in 2045 would mean elevating it 2.2 feet, at a cost of $128 million. To protect against expected flooding levels in 2060, the cost would jump to $181 million.

And all that to protect about two dozen homes.

“I can’t see staff recommending to raise this road,” Haag said. “Those are taxpayer dollars, and as much as we love the Keys, there’s going to be a time when it’s going to be less population.”

The people who live on that 3-mile stretch of road were less understanding. If the county feels that other parts of the Keys ought to be saved, said Leon Mense, a 63-year-old office manager at a medical clinic, then at least don’t make him pay for it.

“So somebody in the city thinks they deserve more of my tax money than I do?” Manse asked. “Then don’t charge us taxes, how does that sound?”

Haag suggested the county could offer residents a ferry, water taxis, or some other kind of boat in the expanding window during which the road is expected to go underwater during the fall high tides.

“If that’s three months a year for the next 20 years, and that gets them a decade or two, that’s perhaps worth it,” she said. “We can do a lot. But we can’t do it all.”

At a climate change conference in Key West, Roman Gastesi, the Monroe County manager, said elected leaders will have to make those difficult calls.

“How do you tell somebody, ‘We’re not going to build the road to get to your home’? And what do we do?” Gastesi asked. “Do we buy them out? And how do we buy them out — is it voluntary? Is it eminent domain? How do we do that?”

Administrators and elected officials are going to have to start to rely on a “word nobody likes to use,” Gastesi said, “and that’s ‘retreat.’ ”

The county’s elected officials must now decide whether to accept that recommendation. The mayor of Monroe County, Heather Carruthers, said she hopes the cost of raising the roads turns out to be lower than what her staff have found, as the need for adaptation leads to better technology.

Still, Carruthers said, “We can’t protect every single house.”

Asked how she expected residents would respond, Carruthers said she expects pushback. “I’m sure that some of them will be very irate, and we’ll probably face some lawsuits,” she said. “But we can’t completely keep the water away.”

Henry Silverman, a retired teacher from Long Island, N.Y., and his wife, Melissa, bought a house on the southern edge of Sugarloaf Key 10 years ago. The building’s first floor is 18 feet off the ground; a boardwalk cuts through a forest of mangroves to a boat launch.

Still, climate change is encroaching on their treehouse paradise. Hurricane Irma in 2017 blew out their screens and pushed water through the windows. Each high tide brings the saltwater a little bit closer, killing the palm trees under the deck and popping the wooden slats off the boardwalk. The couple used to fly down from Long Island in a Cessna, until one day the runway at the island’s airport was underwater.

“What’s government for? They’re supposed to protect your property,” Silverman said.

Mense, who lives in the last house on the road, suggested that officials focus on slowing global warming, without which no amount of adaptation will be enough for these islands.

“Maybe we should think about stopping, or trying to stop, the cause of the water rising,” Mense said. “At what point will the road be high enough?”

Others seemed resigned. Georgia Siegel, a 73-year-old yoga teacher who grew up in Buffalo, N.Y., and moved here 20 years ago, said that if the government decided this area can’t be sustained, she would simply leave.

“What am I going to do?” Siegel asked. “It’s a problem that’s bigger than me.”