DAVOS, Switzerland — Swedish climate activist Greta Thunberg hit back at Steven Mnuchin on Thursday, after the Treasury Secretary suggested she needed to study economics in college before lecturing the U.S. on fossil fuel investments. "My gap year ends in August, but it doesn't take a college degree in economics to realise that our remaining 1,5° carbon budget and ongoing fossil fuel subsidies and investments don't add up," the 17-year-old said via Twitter. "So either you tell us how to achieve this mitigation or explain to future generations and those already affected by the climate emergency why we should abandon our climate commitments," she added. Tweet 1 Mnuchin had criticized Thunberg's financial credentials at the World Economic Forum earlier in the day. Speaking to reporters during a press briefing, Mnuchin was asked whether the world's largest economy should completely and immediately divest from fossil fuels.

Swedish climate activist Greta Thunberg attends a session at the Congres center during the World Economic Forum (WEF) annual meeting in Davos, on January 21, 2020. FABRICE COFFRINI | AFP via Getty Images

That's because Thunberg, alongside 20 other young climate activists, had called on the world's decision-makers and business leaders to stop all investments in fossil fuel exploration and extraction. "Is she the chief economist or who is she? I'm confused," Mnuchin said, before adding this was "a joke. That was funny." "After she goes and studies economics in college she can come back and explain that to us," Mnuchin said.

Carbon budget

An intensifying climate crisis is top of the agenda in Davos, Switzerland. It follows a 12-month period that saw the hottest year on record for the world's oceans, the second-hottest year for global average temperatures, and wildfires from the U.S. to the Amazon to Australia.

Earlier in the week, Thunberg cited the Intergovernmental Panel on Climate Change report from 2018 as she delivered remarks to a packed audience. The IPCC report states the remaining carbon budget would need to fall below 570 gigatons of carbon dioxide in the coming years if the world is to have a 67% chance of limiting global warming to 1.5 degrees Celsius. "With today's emissions levels, the remaining budget is gone in less than eight years," Thunberg said Tuesday. "These aren't anyone's views. This is the science." Thunberg was catapulted to fame for skipping school every Friday to hold a weekly vigil outside the Swedish Parliament in 2018. It sparked an international wave of school strikes — also known as "Fridays for Future" — with millions of children taking part in rallies around the world.

US environmental policies are 'misunderstood'

When asked to address his comments about Thunberg on CNBC's "Squawk Box" on Thursday, Mnuchin said, "Let me just comment because obviously the climate issue is something that is being talked about this week." "And I think, quite frankly, our environmental policies are misunderstood. The president absolutely believes in clean air and clean water. He supports a clean environment." President Donald Trump has often expressed skepticism about the scale of the climate crisis and on Tuesday, he urged participants at the forum to reject the "perennial prophets of doom."