Jeremy Clarkson has made what could be the biggest reversal of his 30-year career. The anti-environmental columnist has, for the first time, accepted the existence of global heating after seeing the impact for himself.

Clarkson’s epiphany came as he and his Grand Tour co-stars ran into difficulty while filming a 500-mile boat race from Siem Reap in Cambodia to Vung Tau in Vietnam.

The group’s jet boats slowed to a crawl and they were forced to wade through Tonlé Sap lake in the usually vast Mekong river system, which has been affected by water shortages.

“The irony is not lost on me,” he told the Sunday Times. “A man who hosted a car programme for 30 years, limited to 7mph by global warming.”

He described enduring “two days of absolute frustration” as the group had to be towed through the river, which had been reduced to a “puddle”.

The former Top Gear host confessed he found the “graphic demonstration” of global warming “genuinely alarming”.

However, Clarkson does not appear to have yet embraced the green movement he once dismissed as “eco-mentalists”. “But we don’t blame mankind for it,” he said. “We’ll let Greta [Thunberg] do that.”

He took yet another dig at the 16-year-old Swedish campaigner in his interview, accusing Thunberg of having no answers to the climate crisis. “‘Ooh, we’re all going to die.’ Right, tremendous. Now go back to school,” he said. “But I genuinely hope people people are working on what on earth to do about it.”

Clarkson had previously used his column in the Sun to label Thunberg a “spoilt brat”, following her speech at the United Nation’s climate action summit in September.

“How dare you,” Thunberg scolded world leaders at the New York summit. “‘You have stolen my dreams and my childhood with your empty words.”

In 2009, environmental campaigners dumped manure on Clarkson’s lawn in response to his attitude to global heating.

Grand Tour, the lavishly funded series that Clarkson started after his acrimonious departure from the BBC’s Top Gear, returns to Amazon Prime on 13 December.

The BBC revealed on Saturday that Thunberg will guest-edit a Christmas special of Radio 4’s Today programme. The campaigner is set to speak to leading figures in the fight against global heating and has commissioned reports from the Antarctic and Zambia.