Greta Thunberg and Donald Trump have traded veiled barbs at Davos as climate change and sustainability lead the agenda at the World Economic Forum.
The teenage activist told the world's political and business leaders that the global youth movement inspired by her school strikes are “just the very beginning” and warned Mr Trump's pledge to join an initiative to plant one trillion trees was "nowhere near" the action required to avert catastrophe.
Despite his tree-planting vow, Mr Trump decried climate "prophets of doom" during his address to delegates and said the US would defend its economy, extolling the benefits of oil and gas. It comes on the same day that his impeachment trial in the Senate begins in earnest.
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"It wasn't only me, but all these young people pushing together ... to form these alliances," the Swedish teenager said, speaking at a panel awith other young activists.
However, Ms Thunberg added that the struggle against climate change will require more than just general awareness.
"This is just the very beginning," she said, adding that everyone needs to listen more to the science regarding climate change and the heating of the planet. Without treating it as a real crisis we cannot solve it."
Trump: Me and Xi Jingping "love each other"
Mr Trump says the relationship between the US and China has never been better.
He added that he and Chinese president Xi Jinping "love each other" and that trade talks with China will be starting very shortly.
"This is not a time for pessimism," he said. "This is a time for optimism."
Donald Trump concluded his 30-minute speech by touting his contribution to clean energy and announcing that the US would be signing up for the One Trillion Trees replanting initiative.

Nobel prize-winning economist Joseph Stiglitz has criticised Donald Trump's speech at Davos for misrepresenting the economy and failing to address climate issues.
Stiglitz said right after the speech that Trump's characterisation of the economy is "totally wrong".
"Our house is still on fire, your inaction is fueling the flames by the hour. We are telling you to act as if you love your children above all else."
Nobel Prize-winning economist Joseph Stiglitz has shot down Donald Trump’s speech at the World Economic Forum for misrepresenting the economy and failing to address the problem of climate change.
Mr Stiglitz immediately rejected the speech and argued that “the characterisation of the economy is totally wrong”. “He managed to say absolutely zero on climate change,” he added.
"The habit of giving priority to (Gross Domestic Product) over the well-being of citizens has got to stop," she said.

