Better understood is the role of carbon dioxide as a greenhouse gas. The safe-operating-zone boundary for CO2 had previously been estimated at levels up to 350 parts per million.

To the Ends of the Earth: The Natural World - Pushing Boundaries is available to stream on pbs.org and the free PBS App, available on iPhone, Apple TV, Android TV, Android smartphones, Amazon Fire ...

More than 200 wildfires are raging across Canada, sending a thick blanket of choking smoke through the U.S. Midwest. Experts says climate change means U.S. residents better get used to it.