A single summer stole more than 200 feet (60 meters) of ice from the snout of Sólheimajökull, a glacier in Iceland, seen in April 2006. James Balog/National Geographic
What a difference a few months made for Sólheimajökull, seen from the same vantage in October 2006. The glacier has withdrawn a third of a mile (0.5 kilometer) over the past decade, in step with rising temperatures. James Balog/National Geographic
Years ago, says a veteran skier, "conditions were fantastic" at the world's highest ski area, on 17,250-foot (5,260 meters) Chacaltaya Glacier near La Paz, Bolivia. Bernard Francou/National Geographic
Today, few attempt the ski run down Bolivia's Chacaltaya Glacier, even after a snowfall. The glacier has shriveled in the past decade, turning much of the slope into a boulder field. Bernard Francou/National Geographic
As icons such as Montana's once well-formed Grinnell Glacier vanish, "people feel a sense of loss," says Dan Fagre of the USGS. T.J. Hileman/Glacier National Park Archives/National Geographic
Montana's Grinnell Glacier, a robust body of ice decades ago, is melting. James Balog/National Geographic
Mount Everest's East Rongbuk Glacier lost some 350 vertical feet of ice between August 1921 (above) and October 2008 (next). Maj. E.O. Wheeler/Royal Geographical Society/National Geographic
Mount Everest's East Rongbuk Glacier lost some 350 vertical feet of ice between August 1921 (previous) and October 2008 (above). David Breashears/National Geographic
Columbia Glacier in Alaska has retreated 11 miles since 1980. Since then, it has diminished vertically an amount equal to the height of New York's Empire State Building. James Balog/National Geographic
Columbia Glacier in 2012. James Balog/Matthew Kennedy/Extreme Ice Survey/National Geographic
The November 2015 issue of National Geographic magazine. National Geographic