A channel big enough to handle global shipping would require deep dredging throughout Lake Nicaragua, the largest source of fresh water in Central America. Esteban Felix/AP hide caption

itoggle caption Esteban Felix/AP

Until recently, finding characteristic stone and bone tools was the only way to trace the fate of the Clovis people, whose culture appeared in North America about 13,000 years ago. Sarah L. Anzick/Nature hide caption

itoggle caption Sarah L. Anzick/Nature

Clive Hamilton's new book Earthmasters. Courtesy of Yale University Press hide caption

itoggle caption Courtesy of Yale University Press

The Climate Casino by William Nordhaus looks at the economics and politics of global warming. Courtesy of Yale University Press hide caption

itoggle caption Courtesy of Yale University Press

Massive sections of ice (center front) have broken away from the Jakobshavn glacier into the sea. There's enough water stored in Greenland's glaciers to raise the sea level by 20 feet. Ian Joughin/Science/AAAS hide caption

itoggle caption Ian Joughin/Science/AAAS

Love your hair. Artists' depictions of a Neanderthal man and woman at the Neanderthal Museum in Mettmann, Germany. Martin Meissner/AP hide caption

itoggle caption Martin Meissner/AP

Each year, 6 to 8 percent of the global population of sharks and rays gets caught, scientists say. The fish can't reproduce fast enough to keep pace Mike Johnston/Flickr hide caption

itoggle caption Mike Johnston/Flickr

A sperm whale entangled in a drift net. A report says commercial fisheries around the world kill or injure 650,000 mammals a year. Alberto Romero/Marine Photobank hide caption

itoggle caption Alberto Romero/Marine Photobank

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

Southern California's San Onofre Nuclear Generating Station, shown here in April 2012, was closed after small radiation leaks. Lenny Ignelzi/AP hide caption

itoggle caption Lenny Ignelzi/AP