Carbon dioxide concentrations in the atmosphere have crossed a major threshold: 400 parts per million. Here are five key points on how carbon dioxide is affecting Earth’s atmosphere and the role we're playing in it.

The last month has seen a trail of smashed records across the central United States, as pulse after pulse of cold air careened down the Great Plains. How does this fit into the bigger picture of a warming U.S. climate?

Forests across western North America have been ravaged by the most extensive bark beetle attacks on record. Scientists are getting a better handle on what comes next—and the answers aren’t as straightforward as they expected.

Reducing emissions of four shorter-lived pollutants could slow the annual rate of sea level rise by up to 50 percent.

A new study by an NCAR researcher shows that small- to moderate-size volcanoes have helped slow down warming over the last decade, while industrial emissions of Sun-blocking sulfur dioxide over Asia have contributed relatively little to the slowdown.