Schemes to mute the impact of climate change such as wider use of drought-resistant crops, irrigation or better forecasting of storm surges could show how to help protect hundreds of millions of people this century, it said.

Achim Steiner, the head of the U.N. Environment Programme (UNEP), said that U.N.-led climate efforts had so far focused most on ways to cut greenhouse gas emissions, rather than helping people adapt to effects such as erosion or rising seas.

"One of the big missing links has been adaptation," he said of the report issued at 190-nation climate talks in Bali, Indonesia. About 350 experts made 24 studies around the world in a $9 million assessment of ways to adapt to a warmer world.

Steiner said the report gave "a foundation upon which adaptation can become part of country development plans and built into international assistance". Adaptation is likely to cost billions of dollars in coming years.

In the Bara province of Sudan, for instance, a study showed that a shift to small-scale irrigated vegetable gardens and efforts to stabilise sand dunes had helped raise food output.

For Uruguay and Argentina, the report urged "a review of coastal and city defences and of early-warning systems and flood response strategies" along the River Plate.

A study showed the population at risk from floods and storm surges along the delta could triple to 1.7 million by 2070. Property losses could range from $5 billion to $15 billion from 2050 to 2100, assuming one storm surge into Buenos Aires.

RAINFALL

In Gambia, a projected decline in rainfall this century is likely to cut yields of millet, a stable crop. The study showed that new varieties of millet and more use of fertiliser were the most cost-effective measures, rather than extra irrigation.

It also said there were risks of a spread of dengue fever in the Caribbean, with a 2 Celsius (3.6 Fahrenheit) temperature rise likely to triple the number of cases by 2080.

Better education about the risks -- especially that dengue-carrying mosquitoes often bred in water storage drums commonly found outside homes -- could help curb cases.

Researchers said that many of the recommendations would apply, even without climate change blamed on emissions from burning fossil fuels. But they said countries had to take a harder look at threats from a changing climate.

"Adaptation is not an option -- it's essential," said Neil Leary of the International START Secretariat in Washington who led the studies.

The December 3-14 Bali talks are to discuss ways to manage a new "adaptation fund" which has an initial sum of just $36 million but could provide up to $1.6 billion in the period to 2012.