DONALD Trump has hit out at the “prophets of doom” on climate change and insisted he would never let “radical socialists” destroy the American economy.

Speaking at the World Economic Forum in Davos, Switzerland, the US President insisted: “America is thriving, America is flourishing and, yes, America is winning again” as he launched a direct attack on “alarmists,” widely seen as directed at Greta Thunberg, the 17-year-old climate change campaigner from Sweden.

She was in the audience for Mr Trump’s speech and moments earlier had spoken at the international event, saying governments and business leaders had done too little to avoid irreversible climate change.

HeraldScotland: Camley's Cartoon: Thunberg hits out at Trump.Camley's Cartoon: Thunberg hits out at Trump.

“This is not a time for pessimism, this is time for optimism,” declared Mr Trump. “A time to reject the perennial prophets of doom and their predictions of apocalypse. We will never let radical socialists destroy our economy.”

Referring to climate activists, he went on: "These alarmists always demand the same thing: absolute power to dominate, transform and control every aspect of our lives." He branded them the “heirs of yesterday's foolish fortune-tellers".

The President announced the US would join an initiative to plant, restore and conserve 1 trillion trees.

"We're committed to conserving the majesty of God's creation and the natural beauty of our world," he said.

Reeling off a long list of economic statistics on job creation and business investment, Mr Trump insisted the US was “in the midst of an economic boom the likes of which the world has never seen before”.

The President claimed America had pioneered “a new model of trade for the 21st century” and hailed recent trade agreements with China, Mexico and Canada, noting how his relationship with Xi Jinping, the Chinese premier, was “extraordinary”, saying: “He’s for China, I’m for US, But other than that we love each other.”

As Brexit approaches on January 31, Mr Trump played up the prospect of a US-UK trade deal, adding: “We look forward to negotiating a tremendous new deal with the United Kingdom, who have a wonderful new prime minister, who wants to make a deal.”

Shortly after Mr Trump spoke, Ms Thunberg called for urgent environmental action at a session on "Averting a Climate Apocalypse".

Without naming the President, she warned world leaders: "I wonder, what will you tell your children was the reason to fail and leave them facing...climate chaos that you knowingly brought upon them? That it seemed so bad for the economy that we decided to resign the idea of securing future living conditions without even trying?

"Our house is still on fire,” she declared. “Your inaction is fuelling the flames by the hour and we are telling you to act as if you loved your children above all else."

In the 2015 Paris Agreement, countries committed to keeping temperatures well inside two degrees Celsius above pre-industrial times, attempting to keep the rise to 1.5C.

But last year, the Intergovernmental Panel on Climate Change warned the planet was heading instead for a rise of 3.0C.