"The tourism industry is going to double between now and 2020. We cannot afford that the emissions also double in the same time," World Tourism Organisation Secretary-General Francesco Frangialli told journalists during a conference in the Swiss resort of Davos.

In a report prepared for the three-day meeting of scientists, politicians and industry officials, the UN agency said global warming may extend the summers of northern countries such as Canada, Britain and Russia, and create new opportunities for travel in polar regions.

But most sites, particularly in poorer and island nations where tourism can generate up to 40 percent of economic output, were seen at risk from rising world temperatures and resultant environmental shifts.

"There are few other economic activities that are so dependent on climate as tourism," the World Tourism Organisation report noted.

"All destinations will have to adapt at some level," lead author Daniel Scott told the Davos conference.

Beach tourism and winter sports have already felt the pinch of rising temperatures, which scientists say will cause more hot days, strong winds, tropical storms, intense rainfall, droughts and wildfires, the Madrid-based agency said.

Many coastal areas have seen beach erosion from storms, more algae blooms, and jellyfish infestations because of warmer than normal sea temperatures. Mountain resorts have coped with less snow and shorter ski seasons.

THREAT TO SCUBA DIVING

Areas dependent on scuba diving and snorkelling were also seen under threat from climate change.

"Most of the world's coral reefs would die off with only a 3 degree Celsius increase in sea temperatures and the myriad of colourful fish and sea creatures that live in the reefs would also disappear," the report found.

Referring to scientists' findings that projected temperature rises could threaten extinction for up to 30 percent of animal and plant species, the World Tourism Organisation also flagged "a spectacular decrease" in the number of lions, elephants and rhinoceroses in Africa, hurting safari operators.

It also said the Maldives, whose economy relies heavily on tourism, could lose entire islands with a small increase in sea levels, while urban sites such as Venice and lower Manhattan could also be submerged.

While declining to estimate potential losses to the sector from unmitigated climate change, Frangialli warned damage to tourist sites could cause severe job losses and economic disruption.