During a trip to Northern California to discuss the state's wildfire emergency with Gov. Gavin Newsom and other state and federal officials, Trump dismissed the science around climate change.
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Trump renewed his unfounded claim that failure to rake forest floors and clear dead timber is mostly to blame.
California went through its hottest August on record, and so far, 3.2 million acres have burned in the state.
Trump has previously said climate change is a hoax perpetrated by the Chinese, and has rolled back policies aimed at addressing it.
Joe Biden blasts Trump over climate, West Coast fires: 'Another crisis he won't take responsibility for'
Biden blasts Trump over climate change, West Coast fires
When state Natural Resources Agency Secretary Wade Crowfoot pleaded with Trump on Monday to recognize the changing climate, the president mocked the established science.
"If we ignore that science, and sort of put our head in the sand and think it's all about vegetation management, we're not going to succeed together protecting Californians," Crowfoot said to Trump.
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"OK. It'll start getting cooler. You just -- you just watch," Trump responded.
"I wish science agreed with you," Crawfoot pushed back.
"I don't think science knows, actually," Trump countered.
That striking moment came on a day of dueling campaign events, with Trump and Democratic challenger Joe Biden dramatically contrasting their outlooks on climate change - and the impact it has had on the record-setting fires ravaging the West Coast.
Biden later tweeted a two-word message: "Science knows."
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"If you give a climate arsonist four more years in the White House, why would anyone be surprised if we have more of America ablaze? If you give a climate denier four more years in the White House, why would anyone be surprised when more of America is underwater?" Biden said.
Trump's suggestion that the planet is going to start to unexpectedly cool is at odds with reality, experts say.
"Maybe there is a parallel universe where a pot on the stove with the burner turned to high 'starts getting cooler.' But that is not our universe," said Stanford University climate scientist Chris Field.
Ninety-seven percent of climate scientists accept the theory that human-caused global warming is real. One of the 3% who don't was just appointed by the Trump administration to a key position at NASA. David Legates will help direct research in climate science for the federal government.
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The Associated Press contributed to this report.