The French Alps' premier ski destination, Chamonix, lies in the shadow of the Mont Blanc mountain range. Its snow-covered slopes give off a pristine glint in the sunlight. At its apex, Mont Blanc (15,781 feet) overlooks everything, a symbol of the resort's long, rock-ribbed traditions. It is the highest peak in Western Europe. But concerns about air quality, as well as troubling, climate-related changes in the landscape of the surrounding mountains, are causing local government and conservation groups to rethink how much future tourism the delicate ecosystem can handle.