Environment

The rare northern spotted owl species faces habitat loss and, now, intruding barred owls. A biologist, and the federal government, have made a difficult decision — killing one owl to ward off the extinction of another.

An aging tree's girth is good for the planet, scientists say, because it helps it suck more carbon dioxide out of the air. "It's as if, on your favorite sports team, you find out the star players are a bunch of 90-year-olds," one ecologist says.

At the time of the accident, the CDC didn't have a standard for how much of the coal-cleaning chemical is safe in drinking water. So the agency had to come up with one.

Scientists say that the freezing weather can help reduce the population of a beetle that harms trees, as well as other invasive species. In Minnesota, up to 80 percent of the beetle's larvae may die off, buying some time for those who feared its negative effects on the ash tree population.

Pennsylvania is the fastest-growing state for natural gas production, but the development is cutting through swathes of previously unbroken forests. Some scientists say this could affect wildlife, which perform important functions like climate and insect control.

Decades ago, amid fears of rapid population growth, a biologist and an economist made a bet about how many people the planet could sustain. Global population is now estimated to top 7.1 billion. So who won the famous bet?

The U.S. Forest Service has proposed a large salvage logging operation in the area affected by last year's historic Rim Fire, which burned 410-square miles of California's Sierra Nevada. The proposal is meeting stiff opposition from environmental groups who say the land is better left untouched.

European scientists were alarmed in 2008 when they discovered streams of methane bubbles erupting from the seafloor in Norway's high Arctic. This gas, which contributes to global warming, was apparently coming from methane ice on the seafloor. A follow-up study finds that methane bubble plumes at this location have probably been forming for a few thousand years, so they are not the result of human-induced climate change. But continued warming of ocean water can trigger more methane releases in the Arctic, with potentially serious consequences to the climate.

Thirty-four firefighters died in the line of duty this year. The unusually high number is sparking a larger conversation about the dangers firefighters face as more homes are built in and around drought-stricken forests.

Global warming is pushing species like the polar bear to the brink of extinction. It's not a typical conservation problem, so one government biologist discovered the best way he could help save the great white bears was to quit his job.