America comes to an end here. Connected to the marshes and moss-laced bayous of southern Louisiana by two miles of narrow causeway, waters lapping high on each side, Isle de Jean Charles takes you as far into the Gulf of Mexico as you can go without falling in. But the dolour in the salt air is not just about loneliness and separation. It’s about impending demise.

Don’t call it a death sentence – the intention is the opposite – but state officials in late March made the announcement that had been a long time coming. Some on the island, nearly all members of the Biloxi-Chitimacha-Choctaw Indian tribe, met it with relief; others with hostility.

Marking the kick-off of what will be the first climate resettlement of its kind in the entire United States, land had been chosen an hour’s drive to the north for a whole new town to be thrown up. No one will force them exactly, but the intention is clear: to evacuate those still living on the island to the new site, where at present nothing but sugar cane stands, before it is too late.

When that will be depends on whom you ask. But no one disputes that the island is sinking, thanks to a combination of subsidence and rising sea levels. Where there were 22,000 acres in 1955 there are only 320 acres today. Climate change isn’t helping, but the principal problem traces back to the Great Mississippi Flood of 1927 when the corps of engineers responded by building giant levees to constrain the river. The result was stopping the flow of sediment into its delta, which once gave the state’s barrier islands the material to rebuild as fast as they eroded.

The vanishing of Isle de Jean Charles into the waves of the gulf might take another decade or even five. On the other hand, one more big storm could finally end its viability for human occupation for good, flooding homes beyond repair or cutting through the connecting road.

“The next hurricane could force all of them, at that point, to move,” Thomas Dardar notes, navigating his truck along the causeway on Palm Sunday morning. The Chief of the United Houma Nation, another large Louisiana tribe, with several close relatives on the island, has been deeply involved in helping to forge the resettlement plan with the state. He is therefore anxious for it to succeed. But he is equally aware of the multiple hurdles it still faces.

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Success matters because at least in the eyes of Chief Thomas, as well as Pat Forbes, executive director of the Louisiana Office of Community Development which must execute the resettlement, a blueprint is being drawn that one day will be followed by countless other communities confronted by climate extinction, maybe in Louisiana, which is losing coastal territory at the rate of one football field per hour, or elsewhere in the country. Or the world.

“It’s really a test run,” Mr Forbes concedes in an interview from his Baton Rouge office. While Americans may have been displaced by environmental change before, notably in Alaska, no single community has been relocated lock, stock and barrel like this. “We are trying to keep the community intact and ensure that it’s economically and socially vibrant and viable. To our knowledge, it’s unique. There are places around the world who are looking at a similar type of thing but nobody in the US has done this.”

Theo Chaisson wants to know what will become of his marina business if the island is evacuated (David Usborne)

Which makes residents on Isle de Jean Charles canaries in the mineshaft. And if they are not opposed outright, they see problems and pitfalls everywhere, a couple of which emerged at the most recent of the monthly community meetings on the island, instituted by Mr Forbes to make sure their concerns are heard. For example: moving the quick is one thing, but what about the dead? What does the state propose doing about their ancestors beneath the island’s overgrown cemetery? (There may be as many as 200 resting there, but one estimate puts the number at only 50.)

Then there is the matter of Theo Chaisson and the small marina he has run for 30 years at the island’s tip. On our visit it bustled with pleasure-boaters and fisherfolk using the dock and slip. His family left for drier land in 1948, but his business is his livelihood. What will become of it if the island is abandoned? No one knows, and that leaves him unsettled and a little angry. He questions why the $48m (£34m) granted by Washington, specifically the Department of Housing and Urban Development (HUD), to pay for the evacuation hadn’t instead been assigned to build better flood defences.

“I don’t think it’s necessary,” Chaisson, 81, says of the resettlement plan. “This here will go,” he adds, gesturing from the elevated deck at the back of his tackle shop to the dry land still remaining, “but not right now. It’s good for another 25 years for sure, or better.” He expects the state will eventually be forced to offer him cash to shut down, although nothing to that effect is settled yet. “I am not for sale,” he says defiantly. “I’ll tell them, ‘No, no no’” – maybe. “With a lot of money, I might be interested. I might be interested.”

Breaking off repeatedly to greet customers looking to buy bait, cold beers or new hooks for their lines, Chaisson argues people can make up their own minds whether to stay and brave the next hurricane or flee. “The ones that want to go, they left already,” he reckons. “They’ve gone.”

Some have. Scan the creaky wood-framed homes that line the single road on the island, many perched perilously high on 15-foot pilings, and several appear abandoned, doors and windows swung open. The fire station was shuttered long ago. There are only 45 adults and 12 children still living on Isle de Jean Charles, according to state officials. A year ago, there were 93 full-time residents. Some who left took up an offer made last November to move to interim housing in the city of Houma, further inland, while they wait for the new community to be built. But the exodus really began after Hurricane Katrina savaged the island back in 2005.

Ground should be broken at the new site north of Houma by year’s end, and the new town – homes, streets, shops, playgrounds – could be ready by 2022, not just for those still on the island but also those already gone. But there are other legal issues beyond the cemetery and the marina. Will relocation really be voluntary? (Mr Forbes is adamant it will.) If the residents do leave will they have to surrender ownership of their properties? Will they be allowed to visit them? Much depends, Mr Forbes admits, “on how far we can push the federal regulatory structure”. In other words, the money from Washington comes with conditions.

Sitting in shade beneath the stilts of the home that has been in his family for seven generations, Chris Brunet, 52, agrees that the uncertainties still make him wary. “We are working on how we can come out on the better end of the deal,” he explains. But the idea of having to leave has clearly taken root in him. “Eventually, eventually,” he says. “But things can’t be done overnight and that’s what we are dealing with right now in making my decisions. Saying ‘yes’ to it.”

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Legalities aside, it’s also what they will lose that weighs heavily on some. “This is paradise. How do you transpose what you have here into town?” sympathises Chief Thomas, whose own home is on the Houma outskirts. “When you are asking people to give up what they have, it’s like death, they are dying, the community is dying.” Most importantly they will be moving away from the water that has sustained them. “They make a living out here,” notes Theo Chaisson. “What are they going to do when they get there? You think they’ll have oysters in their backyard, speckled trout, red fish, shrimp? No.”

It’s hardest for older residents, who see little attraction in giving up everything they know so late in their lives to avoid a giant storm that could come this year or may not for 10. People like Hilton Chaisson. A cousin of Theo, he raised 18 children in his modest home across from the cemetery but lost four. One drowned at the marina at just four years old. Speaking sometimes in English and sometimes in French, the first language of generations in bayou country until the latter part of the last century, he has trouble remembering his age – it seems he is 70 – but about the proposal to relocate everyone, he is quite clear.

“They will have to move me in a box. I am going to die here,” he grumbles, gesturing to the midway mark of a ground-floor window where the water got to after the last serious hurricane struck this part of the coast. He points too towards the southwest where they usually come in from. The vegetable garden he used to till out back with his grandchildren is useless now, because the saltwater has soaked the ground too often. If his neighbours are ready to uproot themselves and quit their island lives, he says, so be it. But that won’t be him and his brood. “If they want to move let them move, I don’t talk much to them people. I stay over here, I stick to my business.”

Refusing to leave is one thing, but it’s not clear if the state would maintain the island’s shaky infrastructure once the offer to relocate has been made. The mains gas line that used to run out to it under the causeway has already been shut off, though the power lines remain up. At the marina, Theo Chaisson understands he may eventually have no choice but to shut up shop. “The only problem will be if they don’t fix the road, then we are stuck out here or we’d have to get a boat to get out here. I’d just sooner close because I’m not getting in a boat to open a boat launch.”

Despite everything – the suspicion and resistance of some and the maddening number of issues still unresolved – Mr Forbes sees no alternative but to make his plan work. Letting the islanders drown isn’t an option. And, leaving aside Hilton and Theo and a few others, the response to it has been “overwhelmingly positive”, he says.