Donald Trump bragged about saving the United States $1 trillion by signing an executive order withdrawing from the Paris Climate Accord - then celebrated by tossing his used pens into a crowd of adoring fans.

The 47th President began signing executive orders in front of cheering crowds at the Inaugural Parade on Monday afternoon, noting: 'Imagine Biden doing this... I don't think so.' 

After riling the crowd up with an emphatic speech, Trump took a seat and began working his way through a stack of executive orders as they were announced one at a time.

When the time came to sign an order withdrawing from the Paris Climate Accord, Trump whispered off camera: 'It'll save them a trillion dollars.'

Moments later he repeated those words. 'A trillion,' he said. 'It'll save a trillion.'

Trump was directing one of his staff to pass on his message to the fawning crowd.

'Yes sir,' he said.

'We're going to save over a trillion dollars by withdrawing from that treaty,' he told the crowd as President Trump handed him the signed document.

The crowd erupted in cheers at the revelation, prompting Trump to later throw his pens into the packed stands after he'd finished signing his documents.

One by one, the President tossed pens into the crowd, walking across the stage to ensure everyone had a fair chance to score one. 

The 2015 Paris Agreement is voluntary and allows nations to provide targets to cut their own emissions of greenhouse gases from the burning of coal, oil and natural gas.

President Trump has repeatedly said he does not want the United States, a top carbon-polluting nation, to remain in the landmark treaty.

His decision is a blow to worldwide efforts to combat global warming and puts the US at odds with some of its closest allies.

The announcement echoed Trump's actions in 2017 when he announced that the U.S. would abandon the Paris accord, which is aimed at limiting long-term global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels.

About half of Americans oppose withdrawing from the international treaty to reduce greenhouse gas emissions, AP reported, based on a poll conducted in January. 

Only about 2 in 10 US adults are 'somewhat' or 'strongly' in favor of withdrawing from the Paris agreement, while about one-quarter are neutral.

Much of the opposition comes from Democrats - about three-quarters are opposed - but Republicans display some ambivalence as well. Slightly less than half of Republicans are in favor of the move, while about 2 in 10 are opposed.

Laurence Tubiana, CEO of the European Climate Foundation and a key architect of the Paris accord, called the planned U.S. withdrawal unfortunate but said action to slow climate change 'is stronger than any single country's politics and policies.'

'The impacts of the climate crisis are also worsening. The terrible wildfires in Los Angeles are the latest reminder that Americans, like everyone else, are affected by worsening climate change,' Tubiana said. 

The withdrawal process from the Paris accord takes one year. 

Trump's previous withdrawal took effect the day after the 2020 presidential election, which he lost to Biden. Biden instantly reversed the decision upon entering the White House.