Adam Cole/NPR

The Houston Ship Channel is home to a wide range of heavy industry, including chemical processing plants and petrochemical refineries. Richard Harris/NPR hide caption

itoggle caption Richard Harris/NPR

Ira Leifer, next to an RV he has outfitted with methane sensors and other equipment to sniff the air. Richard Harris/NPR hide caption

itoggle caption Richard Harris/NPR

Crew members unload a catch of sockeye salmon at Craig, Alaska, in 2005. Researchers say fish are being found in new areas because of changing ocean temperatures. Melissa Farlow/National Geographic/Getty Images hide caption

itoggle caption Melissa Farlow/National Geographic/Getty Images

Carbon dioxide readings at the Mauna Loa Observatory in Hawaii have reached what atmospheric scientist Ralph Keeling calls a "psychological threshold" of 400 parts per million. The amount of carbon dioxide in the atmosphere has been steadily increasing since near-constant measurements began at the observatory in 1958. Jonathan Kingston/National Geographic/Getty Images hide caption

itoggle caption Jonathan Kingston/National Geographic/Getty Images

Miguel Modestino, a Ph.D. student at the University of California, Berkeley, is part of the team working to create a solar fuels generator at the Joint Center for Artificial Photosynthesis. Roy Kaltschmidt/Lawrence Berkeley National Lab hide caption

itoggle caption Roy Kaltschmidt/Lawrence Berkeley National Lab

Ken Caldeira of the Carnegie Institution for Science takes a water sample during his experiment on part of the Great Barrier Reef. The water is slightly pink because his team is using a dye to trace an acid-neutralizing chemical as it flows across the reef. Richard Harris/NPR hide caption

itoggle caption Richard Harris/NPR

The city of Gladstone near the Great Barrier Reef is the world's fourth largest coal-export hub. Dredges, like one seen here, have turned the harbor brown as they work to expand the coal port. Richard Harris/NPR hide caption

itoggle caption Richard Harris/NPR

Ken Caldeira of the Carnegie Institution for Science takes a water sample during his experiment out on part of the Great Barrier Reef. The water is slightly pink because his team is using a dye to trace an acid-neutralizing chemical as it flows across the reef. Richard Harris/NPR hide caption

itoggle caption Richard Harris/NPR

On Australia's Heron Island, buff-banded rails like this one have become the avian equivalent of a weed. Richard Harris/NPR hide caption

itoggle caption Richard Harris/NPR