Paul McCartney is going after President Trump for refusing to take action on climate change.

The former Beatle told Radio 1 Newsbeat that Trump’s belief that climate change is a "hoax" is “madness," the BBC reported.

McCartney, a longtime vegetarian and green activist, was promoting a new short film about the impact of animal agriculture on the environment, which encourages people to give up meat for one day a week.

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"It's not the total solution, but it's part of the solution,” McCartney said. “A lot of people have been saying this for a long time but there's resistance.”

"Particularly when you've got someone like Trump who says that [climate change] is just a hoax. A lot of people like myself think that's just madness so it's maybe a good time now to try and focus people's attention and say 'look, forget about him we can do something.'"

Trump has refused to say whether humans have caused climate change, which he has previously called a "hoax" perpetuated by the Chinese. He announced in June that he was pulling the U.S. out of the Paris climate agreement.

McCartney met up with 2016 Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE while she was on the campaign trail in Ohio last year, tweeting out a photo.