President Donald Trump tore into environmental "prophets of doom" at the Davos forum Tuesday, rejecting fiery warnings from teenage campaigner Greta Thunberg and talking up his own record in a counterpoint to impeachment back home.

Thunberg was in the audience in the Swiss Alps to hear the typically bullish speech by Trump, delivered just before the US Senate opened the crucial next stage in his trial for abuse of power and obstruction of Congress.

The 50th meeting of the World Economic Forum aimed for a strong focus on climate change but Trump made clear he had no time for Thunberg's warning that "our house is still on fire."

IMAGESOne day before the start of the historic impeachment trial in Washington DC, US President Donald Trump leaves for Davos, in Switzerland. Duration:00:27 IMAGESOne day before the start of the historic impeachment trial in Washington DC, US President Donald Trump leaves for Davos, in Switzerland. Duration:00:27 Photo: AFPTV / Anthony Peltier

Instead, he touted the US economy, which he said was enjoying an "unprecedented" boom thanks to his policies. That was a message he then continued at a dinner meeting with CEOs including Europe's richest person Bernard Arnault of luxury firm LVMH and the Indian steel magnate Lakshmi Mittal.

The Republican was also to meet Wednesday with the president of Iraq and the leader of Iraqi Kurdistan before heading back to Washington.

This will be his first talks with the Iraqi leadership since a US drone strike killed Iran's top military figure and also a senior Iraqi commander in Baghdad, triggering a parliament vote calling for the expulsion of US troops from Iraq.

Thunberg (L) underlined the message that has inspired millions around the world -- that governments are failing to wake up to the reality of climate change Thunberg (L) underlined the message that has inspired millions around the world -- that governments are failing to wake up to the reality of climate change Photo: AFP / Fabrice COFFRINI

Dismissing scientifically backed warnings that global warming is wrecking the planet, Trump said "we must reject the perennial prophets of doom and their predictions of the apocalypse."

Trump is set to give the first keynote address of Davos 2020 Trump is set to give the first keynote address of Davos 2020 Photo: AFP / JIM WATSON

He claimed that "alarmists" had been wrong over the decades when predicting population crisis, mass starvation or the end of oil.

Trump branded those warning of out-of-control global warming and other environmental disasters "the heirs of yesterday's foolish fortune tellers".

Trump did not even mention global warming.

The risk of global conflict will also be a topic at the forum after a spike in tensions between the United States and Iran The risk of global conflict will also be a topic at the forum after a spike in tensions between the United States and Iran Photo: AFP / Fabrice COFFRINI

He was just as unapologetic over his impeachment, which is now kicking into high gear.

That's "just a hoax," he said, calling the impeachment trial "disgraceful".

Bank that participated in the Davos World Economic Forum in 2019 financing fossil fuels, according to Greenpeace Bank that participated in the Davos World Economic Forum in 2019 financing fossil fuels, according to Greenpeace Photo: AFP / Simon MALFATTO

Large parts of Trump's address sounded like a campaign speech aimed at a domestic audience as much as the Davos gathering of global political and business elites, which began in 1971.

"I'm glad to declare the United States is in the midst of a great economic boom the likes of which the world has never seen before," he said.

Trump arrived in Davos hours before impeachment trial reopens Trump arrived in Davos hours before impeachment trial reopens Photo: AFPTV / Eloi ROUYER

Over and over, Trump brought up statistics he claimed proved his "unprecedented" success, based on slashing environmental protections and renegotiating trade relationships with China and the United States' two huge neighbours Canada and Mexico.

"The American dream is back, bigger, better, stronger than ever before," he said.

Robin Niblett, director of the Chatham House think tank, called Trump's performance "an almost plain vanilla presidential campaign speech, laying out an unassailable set of statistics that tell the Democrats 'good luck taking me on on this, because you won't stand a chance'."

Earlier, Thunberg underlined the message that has inspired millions around the world, saying "basically nothing has been done" to fight climate change.

Speaking calmly and with a wry smile, Thunberg acknowledged that her campaign, which began with school strikes, had attracted huge attention without yet achieving concrete change.

"There is a difference between being heard to actually leading to something," the 17-year-old said.

And despite the focus given by the Davos forum, Greenpeace said in a new report that some of the world's biggest banks, insurers and pension funds have collectively invested $1.4 trillion (1.26 trillion euros) in fossil fuel companies since the Paris climate deal in 2016.

Trump touted the United States as the "number one producer of oil and natural gas" and said he would not let "radical socialists" attack the lucrative industry.

Sustainability is the buzzword at the Davos forum, with heel crampons handed out to participants to encourage them to walk on the icy streets rather than use cars, and the signage paint made from seaweed.

"People are paying a lot more attention" to climate, Eurasia Group president Ian Bremmer told AFP at Davos, adding there was "genuine action by some big players", after investment titan BlackRock said it was partially divesting out of coal.

"But let's be clear -- a big part of this is because we failed for a very long time and governments continue to fail," he added.

Business leaders are likely also to be concerned by the state of the global economy whose prospects, according to the International Monetary Fund, have improved but remain brittle.

The IMF cut its global growth estimate for 2020 to 3.3 percent, saying that a recent truce in the trade war between China and the US had brought some stability but that risks remained.