The process of relocating people from New Orleans should start immediately, as the city has reached a “point of no return” that will see it surrounded by the ocean within decades due to the climate crisis, a stark new study has concluded.

Ongoing sea-level rise and the rampant erosion of wetlands in southern Louisiana will swallow up the New Orleans area within a few generations, with the new paper estimating the city “may well be surrounded by the Gulf of Mexico before the end of this century”.

Low-lying southern Louisiana faces multiple threats, with rising sea levels driven by global heating, compounded by strengthening hurricanes, also a feature of the climate crisis, and the gradual subsidence of a coastline that has been carved apart by the oil and gas industry.

Southern Louisiana is facing 3-7 metres of sea-level rise and the loss of three-quarters of its remaining coastal wetlands, which will cause the shoreline “to migrate as much as 100km (62 miles) inland”, thereby stranding New Orleans and Baton Rouge, according to the study, which compared today’s rising global temperatures with a period of similar heat 125,000 years ago that caused a rise in sea level.

This scenario makes the region the “most physically vulnerable coastal zone in the world”, the researchers state, and requires immediate action to prepare a smooth transition for people away from New Orleans, which has a population of about 360,000 people, to safer ground.

Louisiana has already experienced population loss in recent years, and this trend will accelerate in a disordered way, the paper warns, should no action be taken to confront the perils faced by its largest city and surrounding communities.

“While climate mitigation should remain the first step to prevent the worst outcomes, coastal Louisiana has evidently already crossed the point of no return,” added the perspectives paper, published in the Nature Sustainability journal. A perspectives paper is a scholarly article that provides an assessment, rather than new data.

Billions of dollars have been spent to fortify New Orleans with a vast network of levees, floodgates and pumps erected after 2005’s catastrophic Hurricane Katrina. But the growing threats to the city mean the levees, which already require hefty upgrades to remain sufficient, will not be able to save the city in the long run, the new paper warns.

“In paleo-climate terms, New Orleans is gone; the question is how long it has,” said Jesse Keenan, an expert in climate adaptation at Tulane University and one of the paper’s five co-authors.

Keenan said the timeframe available to plan a retreat isn’t certain but “it’s most likely decades rather than centuries”.

“Even if you stopped climate change today, New Orleans’s days are still numbered,” he added. “It will be surrounded by open water, and you can’t keep an island situated below sea level afloat. There’s no amount of money that can do that.”

City, state and federal leaders should begin work to help support people moving away from the New Orleans region in a coordinated way, starting with the most vulnerable communities, such as those in Plaquemines parish who live outside the levee system, Keenan said.

“New Orleans is in a terminal condition, and we need to be clear with the patient that it is terminal,” he said. “There is an opportunity for palliative care, we can transition people and the economy. We can get ahead of this.”

But, he added, “no politician wants to first give this terminal diagnosis. They will speak about it behind closed doors, but never in public.”

New Orleans faces obvious challenges – situated in a bowl-shaped basin below sea level, the city already has 99% of its population at major risk of severe flooding, the worst exposure of any US city according to a separate study released last week.

“Even compared to all other US cities, New Orleans really stands out, which is alarming,” said Wanyun Shao, a co-author of this study and a geographer at the University of Alabama.

“There is no specific timeline to how long New Orleans has left but we know it’s in big trouble. They are facing one of the highest sea level rises in the world and I don’t know how long human effort can fight against that tide. It’s like a timebomb.”

Shao said she concurred that relocation of people would have to take place. “I know it’s a politically and emotionally charged issue, there are people with a deep attachment to New Orleans,” she said. “But managed retreat, no matter how unappealing it may be, is the ultimate solution at some point.”

A major pressure upon this southern cultural hotspot is that its surrounding land is briskly receding. Since the 1930s, Louisiana has lost 2,000 sq miles of land to coastal erosion, equivalent to the size of Delaware, with a further 3,000 sq miles set to vanish over the next 50 years. The rate of land loss is so rapid that a football pitch-sized area is wiped out every 100 minutes.

To help counter this, Louisiana last decade settled upon a new sort of plan that eschewed building yet more flood defenses and instead sought to harness the Mississippi River’s natural ability to rebuild land. Levees and other infrastructure have, until now, straitjacketed the naturally meandering Mississippi and pushed the sediment it carries straight into the Gulf of Mexico, rather than replenish the coastal wetlands.

The so-called Mid-Barataria Sediment Diversion project, which broke ground in 2023, would help restore a more natural flow in the Mississippi Delta and allow sediment to build up in coastal areas where it has been lost. More than 20 sq miles of new land would be created over the next 50 years under the plan, the project estimated.

However, Jeff Landry, Louisiana’s Republican governor, scrapped the project last year, arguing its $3bn cost was too high and that it threatened the state’s fishing industry. “This level of spending is unsustainable,” Landry said at the time, adding that the project imperiled the livelihoods of “people who have sustained our state for generations”.

Proponents of the project, which was funded via a settlement from BP over the Deepwater Horizon disaster in 2010, decried the decision as disastrous for the state, pointing out fishing communities will need to move anyway because of worsening erosion.

Garret Graves, a Republican former congressman who once led the state’s coastal restoration agency, said Landry was guilty of a “boneheaded decision” that would “result in one of the largest setbacks for our coast and the protection of our communities in decades”.

According to the new research paper, the loss of the sediment diversion plan “effectively means giving up on extensive portions of coastal Louisiana, including the New Orleans area”.

A legal effort to force oil and gas companies to pay for damage to Louisiana’s coastline, meanwhile, is also in doubt. This month, the US supreme court allowed the fossil fuel industry to federally contest a state jury decision that Chevron pay $740m to remedy harm caused to wetlands by dredging canals, drilling wells and dumping wastewater.

“The combination of these decisions is driving a scenario where the state has stopped trying to build land,” Keenan said. “That just accelerates the timeline. They could be buying time, but that option is foreclosed now, meaning it’s a certainty the New Orleans levees will fail again multiple times. The flood water will have nowhere else to go.”

While the US has never wholesale moved a major city before, numerous communities have relocated for economic reasons in the past, with some now being shifted due to the climate crisis, too. In Louisiana, the government could start planning and building appropriate infrastructure in safer areas on the other side of Lake Pontchartrain, the large estuary that sits to the north of New Orleans, Keenan said.

“This could be an opportunity for New Orleans to help migrate people further north, invest in long-term infrastructure and make that sustainable,” Keenan said.

“That exodus has already begun, so if nothing is done, people will just trickle out over time and it will be an uncoordinated mess. The market will speak as people won’t be able to get insurance. Louisiana has to stop the bleeding and acknowledge this is happening. But at the moment there is no plan.”

Timothy Dixon, an expert in coastal environments at the University of South Florida who was not involved in the new paper, said the study “does a nice job” of highlighting the challenge Louisiana faces with subsiding land combined with rising sea levels.

“New Orleans is not going to disappear in 10 years or anything like that, but policymakers really should’ve thought about a relocation plan a century ago,” said Dixon, whose own research has recommended a measured retreat from coastal Louisiana.

“Governments may not have the ability to just command people to leave, but people will volunteer to move and we are seeing that already. I’m not optimistic our political system is capable of dealing with this stuff, it will take leadership and unpopular decisions. Also, many people don’t want to move. They love where they are born.”

Landry’s office was contacted for comment but did not respond.