Holiday-makers from Europe, Canada, the United States and Japan were likely to spend more vacations in or near their home countries to take advantage of longer summers, they said.

In a report prepared for a UN conference on climate change and tourism, they projected that global warming would reduce demand for travel between northern Europe and the Mediterranean, between North America and the Caribbean, and between northeast Asia and southeast Asia.

"The geographic and seasonal redistribution of tourist demand may be very large for individual destinations and countries by mid- to late-century," the agencies said.

"This shift in travel patterns may have important implications, including proportionally more tourism spending in temperate nations and proportionally less spending in warmer nations now frequented by tourists from temperate regions."

However, overall travel demand was expected to grow by between 4 and 5 percent a year, with international arrivals doubling to 1.6 billion by 2020.

In some developing and island states, tourism accounts for as much as 40 percent of national economic output.

Officials from tourism-dependent countries such as the Maldives, Fiji, the Seychelles and Egypt told the conference that shifts in travel choices, and ecological damage from global warming, posed serious threats to their businesses and jobs.

"Tourism is a catalyst to the economy. If you are hitting the tourism sector, automatically this rocks the whole economic machinery," Michael Nalletamby of the Seychelles Tourism Board told the Davos conference.

Christopher Rodrigues, chairman of the British government agency VisitBritain, said the sector needed to find ways to reduce the effects of ever-increasing travel demand on the environment, which in turn affects the industry's health.