PHOTOS: National Parks at Risk

If you look closely, you can see tourists meandering the boardwalk at the edge of the Grand Prismatic Spring in Yellowstone National Park, in Wyoming. The image is part of a new photo exhibit and coffee table book called "Earth From Above" by Paris-born naturalist, author and photographer Yann Arthus-Bertrand. (Yann Arthus-Bertrand, Harry N. Abrams, Inc./AP Photo)