Donald Trump bizarrely downplayed climate change concerns - claiming fire-ravaged California "will start getting cooler" and claiming to know more than scientists.
The US President met with officials as millions of acres of wildfires cause destruction in the state after record temperatures over the summer.
So far 36 people have died in huge blazes in western states since last month, with whole towns destroyed by wildfires.
Trump's presidential rival Joe Biden has branded him a "climate arsonist" and accused him of again failing the American people.
After being warned against "putting our heads in the sand", Trump responded: "OK. It'll start getting cooler. You just watch."
When told there was no science to support this, Trump responded: "I don't think science knows actually."
Footage of the exchange between the US President and Wade Crowfoot, California's Secretary for National Resources, has been widely shared on social media.
Mr Crowfoot, who was wearing a mask while the US commander-in-chief was not, said: "We had temperatures explode this summer.
"You may have learned that we broke a world record in Death Valley. 130 degrees fahrenheit, but even in greater LA 120 plus degrees.
"If we ignore that science, put our heads in the sand and think it's all about vegetation management, we're not going to succeed in protecting Californians."
The grinning president responded: "Okay. It'll start getting cooler. You just watch."
Mr Crowfoot retorted: "I wish science agreed with you."
Trump hit back: "Oh well. I don't think science knows actually."
Joe Biden branded the President a "climate arsonist" for refusing to acknowledge global warming's role in the deadly wildfires.
He said Trump had “failed the most basic duty to a nation” and added: “This is another crisis, another crisis that he won’t take responsibility for."
He continued: “It’s clear that we’re not safe in Donald Trump’s America.”
Dozens of blazes have raged across 4.5 million acres in Oregon, California and Washington states since last month.
They have laid waste to several small towns, destroying thousands of homes and killing at least 36 people.
The fires also have filled the region's air with harmful levels of smoke and soot, bathing skies in eerie tones of orange and sepia.
Ten deaths have been confirmed during the past week in Oregon, the latest flashpoint in a larger summer outbreak of fires accompanied by catastrophic lightning storms, record-breaking heat waves and extreme winds.
