Less than a generation ago, Chacaltaya, outside La Paz, Bolivia, billed itself as the highest ski area in the world. With a summit at 17,785 feet, it offered year-round glacier skiing, even though it was only 16 degrees south of the equator. The glacier melted in 2009, and the ski area no longer operates. Samuel Mendoza, whose father taught him how to operate the jerry-built rope tow, can’t bring himself to leave. He maintains the forlorn lodge, visited by occasional tourists and a few scientists who collect air samples, studying the warming that melted the snow. Why does he persist? “Maybe the snow will come back,” he says. Mendoza participates in religious ceremonies honoring the mountain gods and watches the clouds. “For generations,” a radio voice says, “one generation could predict the future based on the experience of the prior generation.” At Chacaltaya, that is no longer true.