By Christina Larson

Having just written about the efforts of Chinese and Tibetan observers to grasp the impact of melting glaciers (and drying streams) in the Himalayas, I wanted to add a note about another way to visualize changes underway as the planet warms.

During one of his famed attempts to ascend Mt. Everest in 1921, the British adventurer George Mallory and his entourage took photographs of what they saw. In 2007, American mountaineer David Breashears stood in the same place Mallory had been, and his team took a second high-resolution photograph. Breashears, who now works with GlacierWorks and the Asia Society, wanted to record the changes in the ice sheets.

Below is a graphic that combines that 1921 photograph and its 2007 counterpart. Both show the north face of Mt. Everest, as seen from Tibet. The river of ice snaking downhill is known as the main Rongbuk glacier. Here Breashears estimates the glacier has lost 320 vertical feet in ice mass.

Christina Larson is a contributing editor at Foreign Policy magazine and a Schwartz fellow at the New America Foundation. Follow or message her on Twitter at @larsonchristina.