Speaking to world leaders and industrialists on the same day the president bragged about the US economy and attacked climate activists as “perennial prophets of doom”, the 17-year-old Swede said Mr Trump’s vow to plant more trees was sorely inadequate to address the situation.
“’Unlike you, my generation will not give up without a fight. Our house is still on fire,” Ms Thunberg said at the World Economic Forum at Davos, Switzerland, echoing the words she used a year ago at the same event.
“Your inaction is fuelling the flames.”
Mr Trump attacked Ms Thunberg and other activists who have repeatedly urged world leaders to address the crisis they say is rapidly reaching the point where it will soon become too late to act. In a subsequent newspaper interview, Mr Trump repeated his assertion that the teenager was “angry”.
“This is not a time for pessimism. This is a time for optimism,” said Mr Trump. “Fear and doubt is not a good thought process because this is a time for tremendous hope and joy and optimism and action.”
He added: “To embrace the possibilities of tomorrow, we must reject the perennial prophets of doom and their predictions of the apocalypse.”
She added: “Planting trees is good, of course, but it’s nowhere near enough. It cannot replace mitigation.”
The Swede said she was referring to “empty words and promises” by world leaders.
She added: “You say children shouldn’t worry... don’t be so pessimistic and then, nothing, silence.”
Earlier, Mr Trump, 73, who swiftly moved to withdraw the US from the Paris climate accord when he was elected president, and who has pushed policies critics say have further weakened environmental standards, said Washington was signing an agreement to plant more trees.
Ms Thunberg responded without naming the US president, although it was patently clear who she was referring to.
“We need to start listening to the science, and treat this crisis with the importance it deserves,” she said. “Without treating it as a real crisis we cannot solve it.”
Earlier, Ms Thunberg called on world leaders to listen to young activists who have followed her to Davos this year.
“I’m not a person that can complain about not being heard,” she said. “The science and voice of young people is not the centre of the conversation, but it needs to be.”
The world’s top scientists have repeatedly warned that immediate action is required to address the climate crisis.
With the world experiencing record high temperatures and an increase in the incidence of “extreme” events such as Australia’s wildfires, scientists have called on nations to act to try to limit the rise in global temperature of 1.5C.
“We cannot accept insufficient action anymore,” professor Gail Whiteman, director of the Pentland Centre for Sustainability in Business at Lancaster University, said in a statement. “If we’re united behind the science then every decision, every investment, every behaviour should be based on what is taking us in the right direction.”
Meanwhile, the UN High Commissioner for Refugees said the world needed to prepare for a surge in refugees, with potentially millions of people being driven from their homes by the impact of climate change.
“We must be prepared for a large surge of people moving against their will,” said Filippo Grandi. “I wouldn’t venture to talk about specific numbers, it’s too speculative, but certainly we’re talking about millions here.”
Michael Mann, a climate expert and Professor of Earth Sciences at Penn State University, praised Ms Thunberg’s comments.
“Planting trees is a veritable drop in the bucket. We need to solve this problem at its source – fossil fuels,” he told The Independent.
“Trump here is doing the bidding of the fossil fuel interests that run his energy and environmental policy, engaging in an effort to deflect attention away from the need to rein in the fossil fuel industry and transition away from the burning of fossil fuels. Good on Greta for calling out his villainy.”
Additional reporting by agencies