Veu Lesa, a 73-year-old villager in Tuvalu, does not need scientific reports to tell him that the sea is rising. The evidence is all around him. The beaches of his childhood are vanishing. The crops that used to feed his family have been poisoned by salt water. In April, he had to leave his home when a "king tide" flooded it, showering it with rocks and debris.

For Tuvalu, a string of nine picturesque atolls and coral islands, global warming is not an abstract danger; it is a daily reality. The tiny South Pacific nation, only four metres above sea level at its highest point, may not exist in a few decades. Its people are already in flight; more than 4,000 live in New Zealand, and many of the remaining 10,500 are planning to join the exodus. Others, though, are determined to stay and try to fight the advancing waves.

The outlook is bleak. A tidal gauge on the main atoll, Funafuti, suggests the sea level is climbing by 5.6mm a year, twice the average global rate predicted by the UN's International Panel on Climate Change (IPCC). There is not enough data yet to establish a definitive trend but that figure is alarming, implying a rise of more than half a metre in the next century. Most Tuvaluans live just one to two metres above sea level.

Funafuti's tranquil lagoon is adorned by a necklace of cream islets, each one tufted with dense vegetation. There used to be seven. Now there are six. The other one disappeared after a series of cyclones in the late 1990s. First, the palm trees were stripped off, then the sand, then the soil beneath. All that remains is a forlorn scrap of rubble, visible at low tide. It is an ominous indicator, in miniature, of what awaits Tuvalu's larger, populated islands.

Of all the low-lying nations menaced by global warming, little Tuvalu has been most vocal in the international arena. It recognised the threat early on, and successive governments have lobbied hard to alert the outside world to its predicament. The country - formerly one half of the Gilbert and Ellice Islands, a British protectorate - joined the UN and the Commonwealth in order to raise its profile, and sent diplomats on globe-trotting missions.

Six or seven years on, Tuvaluans concluded that the international community - particularly the big industrialised nations puffing vast quantities of carbon dioxide into the atmosphere - does not care. "They never listened when we asked for help," says Enate Evi, director of the Environment Department. "To be honest, I think they only care about themselves, and their economic advantage. That's how it feels, sitting here."

At the primary school in Funafuti, children learn about climate change from the age of six. Most expect to emigrate. "Because my home island will sink under the water, and there will be no place for me to live," explains Vaimaila Teitala, aged 12. Manuao Taloka, 13, says: "Australia and America and England don't take notice of us because we're too small, and they want to keep their factories and cars."

This could be the last generation of children to grow up in Tuvalu, situated in a remote corner of the Pacific, north of Fiji. "When the tide comes, I'll be under the ground," says Temu Hauma, the school principal. "But I'll definitely be encouraging my kids to move. Why stay here if they haven't got a future?"

It is not so much the prospect of the islands gradually being swamped that worries the locals. It is the extreme weather events they are already experiencing, and which will make their homeland uninhabitable long before the land is submerged. The ever-more invasive spring tides, like the increasingly frequent and devastating cyclones, are associated with global warming.

But some Tuvaluans refuse to accept that their nation is lost. Older people in this devoutly Christian country cite God's promise to Noah that the earth will never again be flooded. Others interpret the Bible less literally but question why they should have to leave the country they love. "We are facing the music of climate change but it's not of our making," says Suseo Silo, the government's disaster co-ordinator. His counterpart at the local branch of the Red Cross, Tatua Pese, says: "We don't want to lose our identity, our motherland. I just hope a miracle will happen."

Despair has now given way to defiance, impotence to pragmatism. Tuvaluans are trying to help themselves. They are dreaming up ways to adjust to the changing conditions, and even reducing their own minuscule emissions of greenhouse gases - in the hope of shaming the big polluters into following. Villagers are exchanging taro, their traditional root vegetable, for more saline resistant crops. They are economising on water to cope with lengthening droughts. They are building houses on stilts, to escape the high tides, and assembling survival kits.

But there is a limit to how far you can adapt when your total living space is 26 sq km, most of it pancake-flat and comprising slivers of land that can be walked across in a minute or two. In Tuvalu, there is no continental interior, and hardly any high ground, to retreat to. Nearly half the population lives squashed together on Funafuti's main islet, Fongafale, which is so skinny that, from most spots, you can see the dark blue ocean on one side and the turquoise lagoon on the other.

The widest area contains a runway built by American forces during the Second World War, which the locals - in between the twice-weekly flights from Fiji - use as their backyard. Football and rugby matches are staged on the tarmac. Children hare up and down the runway on bikes. Stray dogs wander across it. People even sleep there on hot nights, to catch the breeze. Just before the plane lands, a fire engine sounds a siren to clear everybody off.

Opposite the airport, in an imposing new building funded by Taiwan, the government is evaluating a recently completed national adaptation plan. But the plan's author, Pone Saavee, has already left for New Zealand and most senior public figures admit, if you probe, that they are formulating their own exit strategy. Tuvalu is losing its best and brightest, and the place has the air of a sinking ship.

Official policy is to assist those who wish to emigrate, but to continue working for Tuvalu's future. "We still haven't given up hope of living here," says Kelesoma Saloa, private secretary to the Prime Minister, Apisai Ielemia. "But, reading the latest IPCC report, and with the icecaps melting so fast, my personal feeling is we're fighting against the impossible."

Tuvaluans are laid-back, charming people. They laugh a lot, even when contemplating their nation's extinction. They live a simple, communal life. The country earns an income from licensing fishing rights. A few years back it sold its internet domain suffix - .tv - for about £25m. A sizeable chunk of that was used to seal Funafuti's dirt roads. The locals, who used to walk or cycle, bought cars and motorbikes. Now the government is trying to persuade them to walk or cycle, conscious of Tuvalu's part, however tiny, in burning fossil fuels.

On the islet of Amatuku, just north of Funafuti, 30 pigs slumber in a pen, blissfully unaware of the modest part they are playing in tackling a global crisis. Their waste is being processed to produce methane gas, which will be piped to households and used for cooking and power. The project was set up by a French charity, Alofa Tuvalu. Such measures, though, will not change much. "We can tell people to turn off lights and recycle rubbish but the sea level will still rise unless the big countries reduce their emissions," says Mr Pese, the Red Cross worker.

Tuvalu's coral reefs are bleaching, and fishermen are having to travel further afield. Mr Salo, the prime minister's aide, says: "There will come a point when we can't grow anything in the ground, when all the trees start dying and we can't get shelter." The king tides are a new phenomenon. When they strike, the land is almost level with the ocean, and waves break right across the island. The water table is so high that it seeps up through the earth. Among the buildings flooded is the Meteorological Office, which has photographs on its wall of children surfing past its front door.

What everyone fears is a cyclone coinciding with a king tide. "It would wipe out most of Funafuti," says Taula Katea, the Met Office's acting director. New Zealand is prepared to take in 75 Tuvaluans a year. But Keitona Tausi, general secretary of the Tuvalu Congregational Christian Church, says: "I'm really against this scheme. People should stay and develop Tuvalu. If we can work together, we can help our country. But not if everyone leaves." Mr Tausi claims some people who have gone to New Zealand regret it. "They gave up good white-collar jobs here, and now they're picking strawberries."

Saufatu Sopoanga, a former prime minister and an eloquent advocate for his nation, is irritated by assumptions that Tuvalu is doomed. "This type of thinking makes donors reluctant to come forward," he says. "How can they say Tuvalu is doomed when they haven't done anything to help us? The leaders of industrialised nations need to do something real, rather than just talk. There's already been two decades of just talking." The fact is that Tuvalu could survive. Drastic cuts in carbon emissions would slow the process of global warming. The countries that have caused its problems could help it find solutions - building well designed sea walls, for instance, or dredging sand from the lagoon to raise the level of the land.

The latter scheme would cost £1.3m - a princely sum for Tuvalu, but a drop in the ocean for Australia or the US, neither of which have signed the Kyoto protocol. It could be argued Tuvalu is a minute place and few outsiders would miss it. It could also be argued wealthy nations have a moral responsibility to assist. Back in Veu Lesa's village, the old man's daughter-in-law, Lei Aso, is feeding her baby, Lilipa. Does she expect her to spend her life in Tuvalu? Lei Aso looks at me with sad eyes and fans herself, silently.
(By Kathy Marks, The Independent, 17/07/2007)