CO2: 431.44 ppmOnce a wildfire starts, it can spread to an area too massive to control.
One climatologist said "a perfect storm" of climate extremes primed the western U.S. for one of its worst fire seasons in a decade. Meanwhile, Canadian wildfire smoke fills the air.
With a heat wave expected to peak in Southern California on Wednesday, forecasters warned of elevated fire risk.
Fire managers try to anticipate nature's next move, placing thousands of firefighters, hundreds of engines, batteries of bulldozers, and fleets of helicopters and air tankers where they'll make the biggest difference.
Environment Canada has issued health warnings after sky over city turns yellow