The Chaparrastique volcano in eastern El Salvador erupted on Sunday. Hector Garay/Telenoticias 21/AFP/Getty Images hide caption

itoggle caption Hector Garay/Telenoticias 21/AFP/Getty Images

The sea ice that polar bears use as a platform to catch seals is shrinking, threatening the species' existence. U.S. Fish and Wildlife Serivce/AP hide caption

itoggle caption U.S. Fish and Wildlife Serivce/AP

The wildfire in Yarnell, Ariz., last June destroyed homes and killed 19 firefighters. Experts say expansion into wildfire-prone areas has created new challenges for firefighters. Andy Tobin/AP hide caption

itoggle caption Andy Tobin/AP

Mountain lion 38F perches in a tree before getting a tracking collar from the Santa Cruz Puma Project. Peter Lollo/KQED hide caption

itoggle caption Peter Lollo/KQED

Ripening fruit in a grove in Plant City, Fla., this month. Florida citrus growers are worried about citrus greening, which causes bacteria to grow on the leaf and fruit, eventually killing the tree. Chris O'Meara/AP hide caption

itoggle caption Chris O'Meara/AP

A company proposes shipping crude oil by barge across Lake Superior to keep up with the booming supply from North Dakota and Canada. Jack Rendulich/AP hide caption

itoggle caption Jack Rendulich/AP

Workers in Oakland, Calif., check the damage to Interstate 880 on Oct. 19, 1989; this portion of the freeway had collapsed during the Loma Prieta earthquake two days earlier. Paul Sakuma/AP hide caption

itoggle caption Paul Sakuma/AP

Strong gusts in Palm Springs, Calif., generate plenty of energy, thanks to turbine farms. But being able to store all of that energy is just as important. Kevork Djansezian/Getty Images hide caption

itoggle caption Kevork Djansezian/Getty Images

Retired farmer Joe Govert looks at a parcel of family land near Tribune, Kan. It has been enrolled in the Conservation Reserve Program. Charlie Riedel/AP hide caption

itoggle caption Charlie Riedel/AP