TARAWA (Kiribati) • One clear day last winter, a tidal surge swept over an ocean embankment in the remote, low-lying Pacific island state of Kiribati, smashing through the doors and windows of Betio Hospital and spewing sand and debris across its maternity ward.

Mr Beero Hosea cut the power and helped carry frightened mothers through the rubble and water to a nearby school.

"If the next one is combined with a storm and stronger winds, that's the end of us," said the 37-year-old handyman. "It's going to cover this whole island."

For years, scientists have been predicting that much of Kiribati may become uninhabitable within decades because of an onslaught of environmental problems linked to climate change. And for just as long, many here have paid little heed.

But while scientists are reluctant to attribute any specific weather or tidal event to rising sea levels, the tidal surge last winter, known as a king tide, was a chilling wake-up call.

"It shocked us," said pastor Tean Rube of the Kiribati Uniting Church. "We realised, OK, maybe climate change is real."

Pacific island nations are among the world's most physically and economically vulnerable to climate change and extreme weather events such as floods, earthquakes and tropical cyclones, the World Bank said in a 2013 report.

While world powers have summit meetings to negotiate treaties on how to reduce and mitigate carbon emissions, residents of tiny Kiribati, a former British colony with 110,000 people, are debating how to respond before it is too late.

Much of Kiribati, a collection of 33 coral atolls and reef islands scattered across a swathe of the Pacific Ocean about twice the size of Alaska, lies no higher than 1.8m above sea level. The latest climate models predict the world's oceans could rise by 1.5m to 1.8m by 2100.

The prospects of rising seas and intensifying storms "threaten the very existence and livelihoods of large segments of the population", the government told the United Nations in a report last year. For instance, half of the 6,500-person village of Bikenibeu could be inundated by 2050 by sea-level rises and storm surges, according to a World Bank study.

The study lays out Kiribati's future in apocalyptic detail. Causeways would be washed away, crippling the economy; degraded coral reefs, damaged by warming water, would allow stronger waves to slam the coast, increasing erosion, and would disrupt the food supply, which depends heavily on fish supported by the reefs. Higher temperatures and rainfall changes would increase the prevalence of diseases such as dengue fever and ciguatera poisoning.

Even before that, scientists and development experts say, rising sea levels are likely to worsen erosion, create groundwater shortages and increase the intrusion of salt water into freshwater supplies.

In response, Kiribati (pronounced KEE-ree-bas in the local language) has essentially been drawing up plans for its demise. The government has promoted "migration with dignity", urging residents to consider moving abroad with employable skills. It bought nearly 2,500ha in Fiji, an island nation more than 1,600km away, as a potential refuge. Fiji's higher elevation and more stable shoreline make it less vulnerable.

Mr Anote Tong, a former president who pushed through the Fiji purchase, said it was also intended as a cry for attention from the world.

"The issue of climate change is real, serious, and we'd like to do something about it if they're going to take their time about it," he said in a recent interview.

But packing up an entire country is not easy, and may not be possible. And many Kiribati residents remain sceptical of the need to prepare for an eventuality that may be decades away.

The sceptics include the rural and less educated residents of the outer islands who doubt they could obtain the skills needed to survive overseas, and Christians who put more faith in God's protection than in climate models.

"According to their biblical belief, we're not going to sink because God is the only person who decides the fate of any country," said news editor Rikamati Naare at Radio Kiribati, the state-run broadcaster.

As Mr Tong became a climate change celebrity, invited to speak at conferences around the world, opponents accused him of ignoring problems back home, such as high unemployment and infant mortality. They derided the Fiji purchase, for nearly US$7 million (S$9.5 million), as a boondoggle; dismissed his "migration with dignity" as a contradiction in terms; and called his talk of rising sea levels alarmist and an affront to divine will.

Mr Tong, having served three terms, was not allowed to run for re-election this year, but in March elections the opposition defeated his party.

Newly elected President Taneti Maamau plans to shift priorities. "Most of our resources are now diverted to climate change-related development, but in fact there are also bigger issues, like population, the health of the people, the education of the people," he said during an interview at Parliament, which sits on reclaimed land at the edge of a turquoise lagoon.

"Climate change is a serious issue, but you can't do very much about it, especially if a big hurricane comes," he added with a hearty laugh.

The Fiji purchase was not the first effort to address Kiribati's perilous future. The World Bank-led Kiribati Adaptation Programme, begun in 2003, developed water management plans, built coastal sea walls, planted mangroves and installed rainwater harvesting systems. The bank says the project, which cost US$17.7 million, has conserved fresh water in Tarawa and protected about 1.6km of Kiribati's 1,150km of coastline.

But a 2011 government-commissioned report cast doubt on whether the World Bank project helped Kiribati prepare for climate change. And while the mangroves and water management plans have helped, a 2014 study said the first round of sea walls, made of sandbags, had proved counterproductive and caused more erosion.

"Adaptation is just this long, ugly, hard slog," said the study's lead author Simon Donner, a professor of geography at the University of British Columbia in Vancouver. "The idea that an outside organisation can just come in with money, expertise and ideas and implement something easily is naive. What you need is consistent, long-term funding - the type of stuff that's hard to pull off with development aid."

Mr Denis Jean-Jacques Jordy, a senior environmental specialist at the World Bank, acknowledged "we had some issues" with the first sea walls but said subsequent ones made of rock were better designed.

There is no shortage of ideas to avert Kiribati's environmental fate. China's construction of artificial islands in the South China Sea shows the promise of sophisticated island engineering technology, experts say. Mr Tong commissioned a study on raising Kiribati's coastline.

But such measures are financially unrealistic for a resource-poor, aid- dependent state like Kiribati. "It's not about the place going underwater," Prof Donner said, noting that some of Kiribati's islands had actually grown because of land reclamation or natural coastal dynamics. "It's about it becoming prohibitively expensive to live in. That's the real challenge for Kiribati."

The parallel fresh water crisis is also fixable, at a cost. Clean drinking water is scarce on several islands, and salt water from high ocean tides has infiltrated some wells. Many residents of South Tarawa, home to half the country's people, now get their drinking water exclusively from rainwater tanks. Experts worry that as sea levels rise, Kiribati's fragile groundwater supply will face even greater risks, while the next drought could quickly exhaust the municipal supply and household rainwater tanks. Kiribati could invest in desalinisation equipment or ship in drinking water, but this is a country with only one paved road.

"It's all doable," said Mr Doug Ramsay, the Pacific Rim manager at the National Institute of Water and Atmospheric Research in New Zealand. "It's just going to be a very expensive exercise."

Another novel response gaining attention lately is the idea of applying international refugee law - largely drafted after World War II to protect people fleeing political, religious or racial persecution - to those forced from their homes because of climate change.

In 2012, a migrant worker from Kiribati, Mr Ioane Teitiota, applied for asylum in New Zealand, arguing that he was unable to grow food or find potable water in Kiribati because of saltwater intrusion. His lawyer, Mr Michael Kidd, said the distinction between environmental and political refugees was arbitrary. "You're either a refugee or you're not," he said in an interview.

The courts rejected the argument, and Mr Teitiota was deported from New Zealand last year. Mr Kidd said he had appealed to the Office of the UN High Commissioner for Human Rights.

Still, migration may become increasingly important. Mr Tong said he hoped to prepare his people to move with job-training programmes that would meet standards recognised in Australia and New Zealand. "The science of climate change is not 100 per cent precise," he said in the interview. "But we know without any argument that, in time, our people will have to relocate unless there are very, very significant resources committed to maintain the integrity of the land."

Coastal threats are increasingly clear to residents of Buariki, an oceanside village of thatched-roof huts and towering coconut palms on the island of North Tarawa. Erosion along the beach has toppled dozens of coconut trees. The World Bank estimates that 18 per cent to 80 per cent of the village, which sits on a narrow peninsula, may be underwater by 2050.

Some villagers said they were resigned to leaving. "Our government already has land in Fiji for the Kiribati people, so if there are more high tides here, they'll bring people to live there," said 29-year-old Kourabi Ngauea, adding: "But it depends on the government, and if they can support us."

Others see no need to leave. "This is where I belong," Ms Aroita Tokamaen, 76, said as she peeled a coconut on her patio. "I would rather stay."

NEW YORK TIMES