They are the poster children for fears that rising sea levels will swallow island nations.

But a study of Pacific Islands over the past 60 years shows many are fighting back against climate change by actually increasing in land area.

Aerial photographs and high resolution satellite images of 27 islands taken since the 1950s found only four islands had decreased in land area - despite sea level rises of about 12cm - and most of those were uninhabited.

At the same time, seven islands grew in tiny Tuvalu, the low-lying group whose fate transfixed the world's media at the Copenhagen climate conference last year.

The study did not include Tuvalu's most populous island.

In neighbouring Kiribati, the three most densely populated islands increased in size by between 12 and 30 per cent over 60 years.

Paul Kench of Auckland University's School of Environment, who co-authored the study with Fiji's Arthur Webb, said the study suggested the islands had a natural ability to respond to rising seas by accumulating coral debris from the reefs that typically surround them.

"It has long been thought that as the sea level goes up, islands will sit there and drown. But they won't," he said in an article published today in New Scientist magazine.

The study offers hope to thousands of low-lying Pacific islands, whose fate has been one of the most pressing issues for policy-makers dealing with the ramifications of climate change.

Dr Kench told the Herald that for decades islanders had feared their only escape from rising seas would be to move to Australia or New Zealand.

"What we are saying [to island-dwellers] is that now there is a slightly better prognosis, that you will have land," he said.

However, he added: "We are not trying to undersell the fact that you have quite serious environmental challenges ahead of you."

Much depends on how coral reefs react to changing seas.

In the short term, coral dying from warmer seas could feed more sand to vulnerable islands. But it could also have the opposite effect, said Dr Kench.

He said as sea levels rose, more waves hitting the reefs could push more sand on to the islands. "But what that also means is that in storms waves go right over the top of these islands."

Some changes could destroy the groundwater needed to support villages and crops.

He said people on some islands were already moving to take advantage of new land.

In coming centuries it was possible some islands could be abandoned while they built up and re-inhabited once they increased to a stable level.

He said more work was needed to tell residents which islands would be the most stable, which would grow and which would move over time.

UP AND DOWN
* 27 islands studied.
* Four shrunk; 23 stayed the same or grew.
* In Tuvalu: seven islands in one of the nine atolls grew more than 3 per cent on average.
* Study did not include Tuvalu's most populous island.
* In Kiribati: Three most populous islands, Betio, Bairiki and Nanikai, each grew between 12.5 and 30 per cent.

Source: New Scientist magazine.