A defiant 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 50th meeting of 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 environmental “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 later hit out at political leaders, telling them the world, "in case you hadn't noticed, is currently on fire".

In his speech to political and business leaders from around the world, the President, just hours ahead of his impeachment trial at the US Senate, declared: “This is not a time for pessimism, this is time for optimism. 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".

Mr Trump 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, Mr Trump insisted the US was “in the midst of an economic boom the likes of which the world has never seen”.

The President claimed America had pioneered “a new model of trade for the 21st century” and hailed recent 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 emphasised 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 – who rose to prominence after staging a solo “school strike” protest in 2018,which was replicated by schoolchildren across the world - 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 that the planet was heading instead for a rise of 3.0C.

Meanwhile in Washington, senators began the impeachment trial of Mr Trump, only the third president to face the process.

He is accused of:

*pressuring Ukraine to dig up damaging information on Joe Biden, one of his main Democratic challengers in this year’s presidential race, and

*obstructing Congress by refusing to co-operate with its inquiry into the allegations against him.

The President has branded the investigation against him a political “witch-hunt".

A two-thirds majority is needed to remove the President from office; something that has never happened before.

Given the Senate is currently controlled by the Republican Party, a conviction is, therefore, considered highly unlikely in what is a presidential election year.