U.S. Treasury Secretary Steven Mnuchin took time Thursday to advise Swedish climate worrier Greta Thunberg to attend college and study economics before telling others how to manage the planet’s resources.

The topic came up in Davos at the World Economic Forum (WEF) when Mnuchin was approached for comment about the 17-year-old’s warning that the world’s largest economy needed to completely and immediately divest from fossil fuels, AFP reports.

“Does Greta Thunberg’s call for an end to fossil fuel investment threaten U.S. economic growth?” a member of the press asked.

“Is she the chief economist or who is she? I’m confused,” Mnuchin said, before adding this was clearly “a joke. That was funny.”

“After she goes and studies economics in college she can come back and explain that to us,” was Mnuchin’s succinct summation as he elaborated further.

Mnuchin then developed his argument by saying there are no easy choices when it comes to the environment.

He told reporters:

When I was allowed to drive I had a Tesla. I drove in California. I liked it. But nobody focuses on how that electricity is made, and what happens to the storage and the environmental issues on all these batteries. The environmental issues are clearly complicated.

Mnuchin also pointed out America is taking a lead — but through its companies.

If you look at the U.S. from a leadership standpoint – driven by private industry not governent control, we’ve been a leader.

He said people who call for fossil fuel divestment (such as Thunberg this week) do not realise there are significant economic issues, and potential job losses, in simplistic across-the-board solutions.

Many economies are transitioning to more efficient and cleaner energy. That doesn’t have to be all renewables.

The Trump administration and Greta Thunberg have crossed ideological paths before at Davos.

In a speech on Tuesday, U.S. President Donald Trump castigated the “prophets of doom” and those that predicted a climate “apocalypse”, while Thunberg sat silently in the audience.

“These alarmists always demand the same thing – absolute power to dominate, transform, and control every aspect of our lives,” he said. “We’re committed to conserving the majesty of God’s creation and the natural beauty of our world.

Thunberg later repeated her own climate warnings, using her second speech to warn now is the time to “panic” because “the house is burning”, just as she did the previous year in Davos. The teen said:

Unlike you, my generation will not give up without a fight. The facts are clear, but they are still too uncomfortable for you to address. You just leave it because you think it’s too depressing and people will give up. But people will not give up. You’re the ones who are giving up. I wonder what will you tell your children was the reason to fail and leave them facing a climate chaos that you knowingly brought upon them. That it seemed so bad for the economy that we decided to resign the idea of securing future living conditions without even trying? Our house is still on fire.

Thunberg left school in Sweden aged 16 to travel the world and deliver her message of impending climate catastrophe.