Myron Ebell, the longtime climate denier who led President Donald Trump’s transition work at the Environmental Protection Agency up until his inauguration, did not mince words Monday about his disgust with the green movement.

Seeming to echo language often used by the scientific community to describe the climate change crisis, Ebell called the movement to combat it the “greatest threat to freedom and prosperity in the modern world,” The Guardian reports.

Speaking at an event in London hosted by the climate science-denying think tank Global Warming Policy Foundation, Ebell also claimed that the science behind the phenomenon is “vastly exaggerated” and that Trump will, as promised, pull the U.S. out of the Paris climate pact.

“The U.S. will clearly change its course on climate policy,” Ebell told reporters, according to Reuters. “Trump has made it clear he will withdraw from the Paris Agreement. He could do it by executive order tomorrow or he could do it as part of a larger package.”

Ebell is not a member of the Trump administration and admitted Monday that he has never met the president. Still, his prediction may indeed prove true.

Asked during Monday’s press conference if he could confirm reports that Trump planned to withdraw the U.S. from the global pact, White House Press Secretary Sean Spicer said he had no additional information. In April, nearly 200 countries pledged to drastically reduce carbon emissions in an effort to limit the rise in global temperatures.

John Coequyt, global climate policy director of the Sierra Club, was among those who blasted Ebell’s comments, saying that to pull out of the climate pact would be a “mistake of world historic consequence.”

“It’s the kind of wildly irresponsible action that you couldn’t imagine an American president taking until last week,” he said in a statement on Monday. “Our planet is in crisis and we must do everything in our power to tackle it, not move backward.”

In September, U.S. President Barack Obama and Chinese President Xi Jinping fortified commitments to reduce carbon emissions by formally joining the Paris agreement and pledging a “continued bilateral climate cooperation.” The U.S. and China are the world’s two largest emitters of greenhouse gases.

Xi has since warned Trump against withdrawing from the agreement, calling it a “hard-won achievement” that “all signatories should stick to.”

Ebell, who directs environmental and energy policy at the anti-regulation Competitive Enterprise Institute, has a long history of denying climate change and opposing global efforts aimed at combatting it.

In a 2005 column in The Guardian, Ebell wrote that “policies proposed to deal with global warming ― such as the Kyoto protocol ― pose a much greater threat to human flourishing than does global warming.”