Treasury Secretary Steven Mnuchin dismissed criticisms by the climate activist Greta Thunberg on Thursday, saying that she lacked the expertise to call for a complete divestment from the fossil fuel industry.

“After she goes and studies economics in college, she can come back and explain that to us,” he said at a press briefing at the World Economic Forum in Davos, Switzerland, where many world leaders and powerful business figures meet annually.

Ms. Thunberg, a Swedish climate activist who has led demonstrations around the world, spoke at the forum on Tuesday and urged business leaders to stop investing in fossil fuels immediately.

“I wonder, what will you tell your children was the reason to fail and leave them facing the climate chaos you knowingly brought upon them?” Ms. Thunberg, 17, said at the gathering in Davos, a village on the icy reaches of the Swiss Alps. “Our house is still on fire.”