What's fueling today's extreme fires?

Dan Falk, a geophysicist, breaks down the elements of wildfires. "As I write this at the end of July, 79 wildfires are burning across 12 states in the U.S. In Oregon, a mammoth fire has engulfed some 400,000 acres—an area half the size of Rhode Island—and destroyed hundreds of buildings and vehicles, including more than 160 homes. Smoke from wildfires in the western half of the continent has darkened skies over cities in the east, including Toronto, where I am. People in Boston, New York, and Washington D.C. are struggling with hazy, smoke-filled skies". more