As a professional ultrarunner, meaning she competes at distances longer than a marathon, Clare Gallagher has tackled plenty of challenges, from mountains to heat.
But none have been as much of a threat to her career as the U.S. West's worsening forest fires which, fueled in part by stronger droughts linked to climate change, have led to choking air across big swaths of the region each summer.
Fires and poor air quality canceled two major races, last November and in February, said the 27-year-old, who lives in Colorado in the Rocky Mountains region.