The US Treasury Secretary said Swedish climate activist Greta Thunberg is in no position to give economic advice until she’s gone to college and come out with an economics degree.

At a press briefing at the World Economic Forum in the Swiss town of Davos, Steven Mnuchin took a swipe at the 17-year-old environmental campaigner for her recommendation that both the public and private sectors should divest from fossil fuels.

When asked how that would affect the US economic model, Mr Mnuchin questioned Ms Thunberg’s economic credentials.

“Is she the chief economist? Who is she? I’m confused,” he said. Then following a brief pause, he said it was “a joke”.

“After she goes and studies economics in college, she can come back and explain that to us,” he concluded.

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Over the past year, Ms Thunberg has taken issue with many aspects of US policy, not least President Donald Trump’s decision to pull the country out of the Paris accord to limit global warming.

Mr Mnuchin insisted that US policy has been misinterpreted and that Mr Trump “absolutely believes” in a clean environment.

The US, Mr Mnuchin said, has been a leader in reducing carbon emissions.

“What the president objects to is the Paris agreement, because he thought it was an unfair agreement for the United States.”

On Tuesday, Mr Trump used a speech to the forum, which has sustainability as its main theme, to decry climate “prophets of doom”.

Without actually naming Ms Thunberg – who was in the audience at the Swiss ski resort – he called for a rejection of “predictions of the apocalypse” and said the US would defend its economy.

Less than an hour later, the young Swede returned fire in her own speech, telling political leaders the world “in case you hadn’t noticed, is currently on fire”.

Environmental destruction is at the top of the agenda at the annual summit of the world’s decision-makers, which takes place at a Swiss ski resort.

“Our house is still on fire,” Ms Thunberg said, repeating her remarks at the annual meeting of the World Economic Forum a year ago.

“Your inaction is fuelling the flames,” the teenage activist added, in her latest to-and-fro with the 73-year-old President.

Mr Trump announced the US would join an existing initiative to plant a trillion trees, but also spoke at length about the economic importance of oil and gas and called climate change activists “pessimistic” and the “heirs of yesterday’s foolish fortune tellers”.

Ms Thunberg responded by referring to “empty words and promises” from world leaders.

“You say children shouldn’t worry … don’t be so pessimistic and then, nothing, silence.”

– With agencies