Just as the spat between US President Donald Trump and Greta Thunberg seemed to be subsiding, US Treasury Secretary Steven Mnuchin has taken a new dig at the climate activist.

Key points: Mr Mnuchin said environmental concerns need to be weighed against other issues

Mr Mnuchin said environmental concerns need to be weighed against other issues He said the Trump administration's policy on climate had been misinterpreted

He said the Trump administration's policy on climate had been misinterpreted He invited Ms Thunberg to study economics in college and then return to the debate

Asked about Ms Thunberg's call to divest from fossil fuels, Mr Mnuchin told a news briefing: "Is she the chief economist? I'm confused…".

"After she goes and studies economics in college, she can come back and explain that to us."

Mr Mnuchin's quip came two days after Mr Trump and Ms Thunberg sparred indirectly at the World Economic Forum in the Swiss ski resort of Davos.

After Mr Trump said the US had committed to joining the 1 trillion tree initiative, Ms Thunberg retorted that fixing the climate crisis was not only about trees.

Before he left Davos, however, Mr Trump seemed to extend an olive branch, saying he wished he had seen Ms Thunberg speak.

Swedish climate change activist Greta Thunberg says the environment should trump economics. ( REUTERS: Denis Balibouse )

Addressing the Trump administration's stance on climate, Mr Mnuchin said the US position had been "misunderstood".

"There is a real misinterpretation of the US policy. Let me be very clear: President Trump absolutely believes in clean air and clean water and having a clean environment," he said.

Mr Mnuchin later told CNBC he did not believe there were just a few years left to prevent a climate catastrophe.

"There are a lot of other important issues" threatening civilisation, he said, citing health and nuclear proliferation.

"I think that the youth needs to understand: climate is one issue that needs to be put in contexts with lots of other things."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 52 seconds 52 s Mr Trump slams climate activists in his opening address at the World Economic Forum

But German Chancellor Angela Merkel rushed to Ms Thunberg's defence, saying that attaining the goals of the Paris climate accord, which the US has quit, was vital.

"Time is pressing, so we — the older ones, I am 65 years old — must make sure that we take the impatience of young people positively and constructively," Ms Merkel said in her speech to the WEF's annual meeting.