Donald Trump and California state officials sparred over whether climate change is contributing to out-of-control wildfires across the West, after the president insisted that poor forest management drives the conflagrations.

Wade Crowfoot, the secretary of California’s Natural Resources Agency, told Trump in a meeting in Sacramento on Monday that a warming climate is making the state’s fires worse.

“We want to work with you to really recognize the changing climate and what it means to our forests, and actually work together with that science,” Crowfoot told the president. “The science is going to be key. 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.”

Trump responded: “It’ll start getting cooler, you just watch.”

“I wish science agreed with you,” Crowfoot said.

“I don’t think science knows, actually,” Trump responded.

Trump flew into Sacramento after a weekend campaign swing through Nevada in order to discuss the fires with California officials including Governor Gavin Newsom. More than 5 million acres have been burned across the West this season, killing dozens of people and ruining air quality from California to Washington.

Newsom on Friday argued that flawed forest management practices of the past can’t explain the state’s worsening fire seasons. California has been stepping up its use of controlled burns to thin out vegetation and has accelerated cutting fire breaks around vulnerable communities, he said.

But the recent drought and a tree-killing beetle infestation, both of which Newsom tied to climate change, have killed more than 150 million trees across the state, leaving ample fuel for fires.

“I’m not going to suggest for a second that the forest management practices in the state of California over a century-plus have been ideal,” Newsom said Friday in Butte County, surrounded by scorched trees. “But that’s one point. It’s not the point.”

The president has frequently criticized California’s Democratic leaders for, in his view, failing to adequately manage the state’s forests to reduce fire risk.

About 57% of California forests are land owned and managed by federal agencies, according to the University of California. Newsom said Monday that just 3% of the state’s forests are on land managed by the state government.

In August, Newsom’s administration reached an agreement with the U.S. Forest Service to jointly reduce fire risk on at least 500,000 acres of public lands each year.

Trump claimed before the meeting that an unnamed European leader told him his country has more explosive trees than California, before disputing state officials who said climate change was contributing to out-of-control West Coast wildfires.

“I was talking to the head of a major country and he said, ‘We are a forest nation. We consider ourselves a forest nation.’ This was in Europe. I said, ‘That’s a beautiful term,”’ Trump told reporters after landing in Sacramento.

“He said, ‘We have trees that are far more explosive’ — explosive in terms of fire — but ‘we have trees that are far more explosive than they have in California, and we don’t have any problem.’”

Trump said that “I think a lot of things are possible” in response to a question about whether climate change is driving the western wildfires, which have consumed more than 5 million acres, killing dozens of people and ruining air quality on the West Coast.

“With regard to the forest, when trees fall down, after a short period of time — about 18 months — they become very dry. They become really like a matchstick,” Trump said. “And they get up; you know, there’s no more water pouring through, and they become very, very — they just explode. They can explode.”

“Also leaves,” he added, “when you have years of leaves, dried leaves, on the ground, it just sends it up. It’s really a fuel for a fire. So they have to do something about it.”

He said the state should cut more firebreaks through its forests, again comparing California to European forests that he said are better managed.

“They also have to do cuts. I mean, people don’t like to do cuts but they have to do cuts,” he said. “So if you do have a fire and it gets away, you’ll have a 50-yard cut in between so it won’t be able to catch in the other side.

“They don’t do that,” he said of California. “If you go to other countries, you go to Austria, you go to Finland, you go to many different countries and they don’t have problems.”

After taking office, Trump pulled the U.S. out of the Paris climate accord negotiated by President Barack Obama, calling it unfair. On Monday, he suggested the U.S. shouldn’t undertake efforts to mitigate climate change because other countries can’t be trusted to follow suit.

“Is India going to change its ways? And China going to change its ways? And Russia — is Russia going to change its ways?” he said. “You know, so, you have a lot of countries that are going to have to change because they make up — we’re just a small speck.”