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We never expected them to agree.

President Donald Trump and teen climate change activist Greta Thunberg presented starkly differing visions of the challenges facing the Earth at the World Economic Forum on Tuesday — one optimistic, the other an ominous warning for the future.

Speaking just after Trump at the gathering of world business and political leaders in Davos, Switzerland, Thunberg rebutted the one environmental policy the president mentioned in the address Tuesday — a plan to join the Trillion Trees Initiative.

“Planting trees is good of course, but it is nowhere near enough of what is needed,” said Thunberg, whose solo "Fridays for Future" school strikes triggered a global phenomenon drawing millions to the streets to protest climate inaction.

Trump, in a 30-minute address that focused on the strength of the U.S. economy, criticized “perennial prophets of doom” and “the heirs of yesterday’s foolish fortune tellers.”

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Instead, Trump, 73, urged the audience to be optimistic and have faith in future advancements.

“A growing and vibrant market economy focused on the future lifts the human spirit and excites creativity strong enough to overcome any challenge,” he said.

Thunberg’s speech — titled “Averting a Climate Apocalypse” — stood in direct contrast to Trump’s push for positivity.

"Our house is still on fire," Thunberg, 17, said repeating the message she gave last year at the forum.

She stressed that the world doesn’t have time to wait or put its faith in future innovation to solve climate change, and struck out at world leaders for not doing enough to fight the climate emergency.

“We’re not telling you to offset your emissions by just paying someone else to plant trees in places like Africa, while at the same time forests like the Amazon are being slaughtered at an infinitely higher rate,” Thunberg said.

She also pledged that her generation “will not give up without a fight.”

Before Trump's address, a reporter asked him if he thought Thunberg was right on climate change. Instead of ridiculing the teen as he has in the past, the president said that he’s “a big believer in the environment. The environment to me is very important.”

Last month, the president mocked the Swedish teen after she was named Time magazine's Person of the Year, calling her selection "ridiculous" and suggesting she take anger management classes.

He also appeared to jeer at her in September after she gave an emotional speech at the United Nations Climate Action Summit.

“She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!” Trump wrote on Twitter.

Thunberg later updated her Twitter profile with his description of her.