The threatening prongs of climate change creep inward from the coasts. The Tower of London and the Palace of Westminster could both be damaged by more frequent and intense flooding of the Thames River caused by rising sea levels and changing storm patterns, according to a 2007 report by UNESCO's World Heritage Center. The millennium-old buildings survived the bloody English Civil War and the Nazi blitz and now host millions of visitors every year. But the risk of a catastrophic flood is estimated to rise fivefold by 2050, says May Cassar of the Centre for Sustainable Heritage at University College London. "These monuments were inscribed on the World Heritage List for their universal value," she says. Any damage would be "a cultural loss not just to the British but to all of us." Across northern Europe, moreover, rising humidity levels could speed the spread of microbes whose acidic excretions eat away at stone cathedrals and marble monuments, according to a recent European Union-funded environmental study. And at the summit of Kilimanjaro, halfway between sea level and space—and almost halfway between the poles—climate scientists themselves may lose big to climate change: Doug Hardy of the University of Massachusetts is one researcher who has been racing to glean ancient meteorological data from ice cores before they melt away. "We don't have many historical measurements from that part of the planet," he says. "That record of environmental change will be entirely gone in a few decades."
Some menaces are of a more local nature—and can be tackled accordingly. When the Taj Mahal started turning from white to yellow over a decade ago, most likely from airborne pollutants that were staining the grand mausoleum's pearly skin, India's Supreme Court stepped in. Thousands of nearby factories, kilns, and iron foundries have since been moved or closed, and now over 8,000 tourists a day take electric buses and horse-drawn carriages to visit the monument. Yet across Asia and elsewhere, population growth and intensifying urbanization are bound to threaten other such cultural sites, while new roads slice across the paths of migrating species, and slash-and-burn farmers nibble at the edges of nature reserves and virgin forests. And while tourism can be a destination's—even an entire country's—greatest revenue source, it often leaves its own heavy footprints. Hotels, restaurants, airports, and other facilities and services aimed at visitors bring development to the doorstep of some of the world's most delicate places.
Ecuador's Galápagos Islands are a case study in how travelers can be both part of the problem and part of the solution. The unique, fearless wildlife that evolved on the isolated Pacific archipelago draws over 120,000 visitors and $400 million in revenue every year, and the numbers are rising. "These islands are an incredible natural laboratory for evolution," says Michael Romero of Tufts University, who studies native marine iguanas. "You can see the history of life." One can also foresee a potential ecological tragedy. Nonnative plants, animals, and diseases have already ravaged parts of the sensitive ecosystem, and overfishing of marine life is an ongoing problem. More than 1.3 million gallons of diesel fuel for tour boats and generators was shipped in from the mainland last year, and a 2001 oil tanker accident spilled over 130,000 gallons of diesel. "The question," says David Blanton, former director of the International Galápagos Tour Operators Association, "is whether the Galápagos will follow the historic cycle of boom-and-bust tourism development, destroying what originally attracted visitors in the first place."
Hopeful signs. There and elsewhere, measured steps have been taken to safeguard destinations in jeopardy. The same winds that brought Charles Darwin aboard the HMS Beagle in 1835 are now being harnessed to provide the Galápagos with renewable power, reducing dependency on transported fuel. Last fall, three enormous wind turbines were installed on San Cristóbal Island, where most of the archipelago's 20,000 or so inhabitants live, as part of a $10.8 million project to wean the Galápagos from fossil fuels. Professional sharpshooters helped rid Isabela Island of tens of thousands of destructive feral goats, introduced by early sailors, in only six years. Tourism is still highly regulated; only 1 percent of the islands' land area is open to visitors, who must follow professional guides at all times.