Global warming has led to a new travel boom as holidaymakers embrace what tour operators are calling doomsday tourism - the urge to see some of the world's most endangered sites before they disappear for ever. Newly awakened to the perils facing the planet, American tourists are leading the charge to the melting glaciers of Alaska, Patagonia, the Arctic and Antarctic, the sinking islands of the Pacific and the fading glories of the Great Barrier Reef - and their British counterparts are not far behind. A polar bear is seen on the Monaco Glacier, Spitsbergen, No Ken Shapiro, the editor...