Why entertain such dreadful thoughts? Because a growing body of scientific evidence points to a trend that could spell heartbreak for future tourists and catastrophe for many sectors of the tourism industry. Global warming, driven mostly by carbon dioxide and other heat-trapping gases spewed skyward by the world's bustling fossil-fuel economy, could negatively affect many of the world's most-visited tourist destinations within the next few decades.

And tourists themselves, ironically, are contributing mightily to the problem, traveling in ever-higher numbers on a planet where virtually every new snowmobile, jumbo jet, cruise liner, Winnebago, hot tub and air-conditioned hotel ballroom draws power ultimately from oil, gas or coal. These fuels, once burned, add directly to the CO2 load threatening the very destinations people love to visit.

If you have trouble picturing your own favorite getaway spot despoiled by global warming and its seemingly science-fictionlike consequences, consider the physical evidence already on display:

Spawned by just one degree of planetary warming in the 20th century, glaciers worldwide are retreating at breathtaking speed. Spots like Africa's fabled Mount Kilimanjaro will be ice-free in just 15 years and Montana's Glacier National Park will be devoid of glaciers in 70 years if current trends hold, according to recent studies.

Coral reefs, which attract multitudes of flipper-footed tourists to tropical playgrounds worldwide, are likewise in free-fall decline. Twenty-seven percent of the world's reefs have been destroyed in the past 50 years due to rising sea surface temperatures and other factors, and another 32 percent are at risk of dying by 2050, again with water temperature a factor, according to the Global Coral Reef Monitoring Network, an international clearinghouse for coral reef studies in Townsville, Australia.

Far-flung travel guides and outfitters report strange and suddenly unpredictable rainfall patterns worldwide that frustrate tourist activities, and warmer temperatures that could widen the range of malaria-bearing mosquitoes, affecting potentially millions of travelers.

Perhaps the most surreal indication of what might be in store comes from the idyllic, tourist-friendly island nations of Tuvalu and Kiribati, in the South Pacific. Tuvalu is developing concrete emigration plans to evacuate its islands perhaps entirely in this century, migrating en masse to "host countries" like New Zealand. This is because scientists say sea-level rise could inundate Tuvalu and other low-lying island countries almost entirely as polar ice melts and ocean water expands. Rising ocean water in Kiribati is already destroying coastal roads and crops.

Beyond the obvious hardships on local populations, these and other climate-related changes could have a huge impact on many sectors of the travel and tourism business. That industry is now the world's largest, accounting for 11 percent of the world's gross economic product in 1999, with $3.5 billion in direct and indirect receipts, according to the World Travel & Tourism Council (WTTC), an industry trade association based in London.

"Tourism is an industry harmed by any harm to the environment. Period," says Bill Maloney, executive vice president of the American Society of Travel Agents in Alexandria. "Global warming is definitely on our radar screen of concerns."