Dawn illuminates Little Missouri National Grassland in North Dakota. As many as 60 million bison once grazed these lands. Today only about 200,000 remain. Photograph by Phil Schermeister

Fires are rare in the tundra, where "fuel"—in the form of tall plants or trees—is scarce. But as temperatures rise, thicker, taller shrubs are spreading throughout the region, raising the likelihood for more fires in coming years. Tundra burning may also release more organic carbon, a greenhouse gas currently stored in the soil, into the atmosphere. Photograph by Jason Stuckey

Polar bears—like this one leaping between ice floes in Svalbard, Norway's Hinlopen Strait—live on the Arctic ice, hunting seals and other fatty marine mammals. But as the ice vanishes, some experts predict this predator will also disappear from the Arctic by 2050. Photograph by Ralph Lee Hopkins

Here, a large, glistening iceberg calved from the Jakobshavn Glacier in Greenland drifts through Disko Bay on its way to the Atlantic Ocean.