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Mastiff on Mountain, North America, 1967

Photo: Mastiff sliding down snow-covered mountain

Crumbling ice makes for a precarious journey for this mastiff sliding down a slope in North America.

As global warming pushes temperatures higher each year, scientists predict that permanent snow lines of mountains around the world will rise, closing skiing resorts, hurting tourism, swelling major rivers, potentially submerging low-lying areas, and significantly changing landscapes.

(Photo shot on assignment for, but not published in, "Science Finds New Clues to our Climate in Alaska's Mighty Rivers of Ice," February 1967, National Geographic magazine)

Photograph by Christopher Knight