Treasury Secretary Steven Mnuchin mocked Swedish climate change activist Greta Thunberg at the World Economic Forum in Davos, Switzerland, saying she should get an economics degree before lecturing world leaders on policy.

“Is she the chief economist or who is she? I’m confused,” Mnuchin told reporters on Wednesday. He later clarified that his comment was intended as “a joke.”

Thunberg, 17, vaulted to international fame after her climate change activism inspired politicians and celebrities around the world. The teenager warned world leaders that "they haven't seen anything yet," and former Vice President Al Gore this week said that "nobody speaks truth to power" like Thunberg.

Mnuchin brushed off the teenager's activism and urged her to attend college before lecturing leaders around the world.

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

Thunberg told Davos attendees that leaders must "completely divest" from fossil fuels and called investments in fossil fuel exploration and extraction "madness."

[Read more: Trump says he would have ‘loved’ to see Greta Thunberg at Davos: ‘She beat me out on Time magazine']