HARI SREENIVASAN:

California fire officials announce that the massive Carr fire, which burned for over a month this summer in and around the city of Redding has been fully contained. The fires, which began in late July claimed eight lives, destroyed more than a thousand homes and covered over 229,000 acres. Multiple fires continue to burn throughout the western U.S. and wildfire seasons are expected to last longer and burn hotter.

Flames are not the only danger from fires. Smoke can drift for hundreds of miles. The smoke from this year's western wildfires has been observed all the way in New Hampshire, swept toward the east by the jet stream.

A new report by nonprofit science and news organization Climate Central shows that in parts of California as well as Idaho, Oregon and Washington state progress in reducing traditional air pollution is being undermined by wildfires. Senior science writer Jon Upton joined me recently to discuss those implications.

John, when we think about people affected by forest fires, we're usually thinking about those people who have homes that are too close to the fires, they evacuated, they get out of harm's way. But your report really starts to look at a group of people that can't get out of harm's way not from the fire but from the smoke. Explain.