PALM BEACH, Fla. When Brian and Susan Gary settled down on this exclusive island spit a decade ago, climate scientists were already sounding an alarm: Global temperatures were warming, sea levels were rising and damaging floodwaters were creeping ever closer to homes.

The Garys had joined 8 million Americans who moved to counties along the U.S. coast between 2000 and 2017, lured by the sun, the sea and heavily subsidized government flood insurance that made the cost of protecting their homes much cheaper than the risk of living in a flood zone near a vast body of water.

But a reckoning is coming.

On Friday, the Federal Emergency Management Agency was planning to incorporate climate risk into the cost of flood insurance for the first time, dramatically increasing the price for some new home buyers. Next April, most current policyholders will see their premiums go up and continue to rise by 18% per year for the next 20 years.

The price hike under a new assessment, Risk Rating 2.0, will more accurately reflect the threat of flooding in a changing climate, federal officials say.

Most homeowners will see modest increases starting at $120 per year in addition to what they already pay, and a few will see their insurance costs decrease. But wealthy customers with high-value homes will see their costs skyrocket by as much as $14,400 for one year. About 3,200 property owners, mostly in Florida, Texas, New Jersey and New York fall in that category.

Like the climate threat, the cost increase will reach far beyond the coast.

Homeowners in inland states such as Iowa, Missouri and Nebraska, where creeks, streams and rivers overflow during heavy rains, will also see price increases in their government-backed flood insurance.

Climate change will affect people who weren’t threatened before. New technology that allows analysts to study the environs around each home led to a stunning find: 6 million homes in states such as Utah, Idaho, Vermont and Tennessee that didn’t require insurance because they were thought to be safe from flooding are actually at risk because of climate change.

Another 2 million homes across the country will fall into the risk group within 30 years as the climate changes, according to First Street Foundation, which developed the new flood-risk rating for FEMA.

“It doesn’t matter if you believe in climate change; your insurance company does,” said Nick VinZant, senior research analyst for QuoteWizard, a subsidiary of Lending Tree, the online mortgage company. “The realities of that are going to be reflected moving forward.”

One reason the old pricing had to go, VinZant and others said, was its inequity. FEMA generally assessed flooding risks to homes based on zones, so that people with lower-value homes paid about the same rate as wealthy people with high-value homes.

Moderately priced homes were overinsured and million-dollar mansions were underinsured. In a nutshell, middle-income policyholders were helping to subsidize the rich.

“It is now going to say if you’re in a risky place, you’re going to get charged more for it, and other people aren’t footing the bill,” VinZant said.

Homeland Security Secretary Alejandro Mayorkas said in April that Risk Rating 2.0 “aligns with the Biden administration’s priority to . . . tackle the effects of climate change and eliminate inequities in the delivery of federal programs.”

But it’s unclear how long Risk Rating 2.0 will survive. Wealthy policyholders in coastal states are complaining, and members of the House and Senate are listening.

In the Senate, Majority Leader Chuck Schumer, D-N.Y., sought to extend the current system by another five years. In the House, Rep. Charlie Crist, D-Fla., led a bipartisan group in demanding changes to the increases.

Thirty-eight members signed a letter in September expressing their concern over “the burden of potential double digit rate hikes on our constituents” and asked for a delay. Congress can pass legislation that could derail the price increase. (Only three of the signees represent landlocked states.)

Congress has increased flood insurance rates before, in 2012. But it reversed those increases two years later after some communities protested.

Flooding is the most common and costly type of natural disaster in the United States. A 2017 report by the Union of Concerned Scientists said 170 coastal communities will face chronic flooding – at least 26 times a year – in the next two decades. That’s twice as many at-risk locations as today.

More than 5 million people have government-backed flood insurance, which provides $1.3 trillion in coverage in 22,550 communities across the United States. As of last year, the National Flood Insurance Program (NFIP) run by FEMA was $20 billion in debt from massive payouts to people with subsidized insurance.

Officials at the NFIP started talks about a new pricing structure in 2015, said Roy Wright, a former executive director of NFIP who currently directs the Insurance Institute for Business and Home Safety.