Even 16,500 feet in the air, perched on the steep slope of a volcano in Ecuador, French glaciologist Bernard Francou moves gracefully. Hopping among ice blocks and jagged rock debris, he stops suddenly before a boulder with blue letters painted on its surface. The thinker: Bernard Francou. Photo: Bernard Pouyaud, Ecuador Instituto Nacional de Meteorologia e Hidrologia. "This is where the glacier stopped when I first came here seven years ago," Francou explains, oblivious to the cold and the drizzle. He then points more than a football field's distance uphill, where a wall of blue ice marks the present-day terminus …