US congressional Democrats led by House Speaker Nancy Pelosi, eager to repair damage caused by the US withdrawal from the Paris Agreement under Donald Trump, told COP26 on Tuesday that "America is back" to lead on climate.

The 20-strong delegation at the UN climate talks included the chairs of key committees in the US House of Representatives, along with junior members such as Alexandria Ocasio-Cortez, elected in 2018 in part on a platform of action to confront the threat of global warming.

"America is back on the international stage as a leader on climate action and drawdown" of greenhouse gas emissions, said Ocasio-Cortez, a main architect of the Green New Deal that helped shape major pieces of legislation.

On Saturday, US President Joe Biden hailed the passage of his $1.2 trillion dollar infrastructure plan, which includes billions for electric vehicle charging stations, and tens of billions for climate resilience measures.

A vote, however, on the even bigger Build Back Better bill, which earmarks hundreds of billions for climate action, has been delayed and its passage -- at least as currently written -- remains in question.

US Speaker of the House Nancy Pelosi speaks at a session during the COP26 UN Climate Change Conference in Glasgow on November 9, 2021
US Speaker of the House Nancy Pelosi speaks at a session during the COP26 UN Climate Change Conference in Glasgow on November 9, 2021 AFP / Paul ELLIS

"We come here equipped, ready to take on the challenge and meet the moment," Pelosi said at a second press conference.

"This is all about the children, leaving them a world were they can be healthy, more secure, and more in reach of their fulfullment."

Congresswoman Veronica Escobar, whose district includes the city of El Paso straddling the US-Mexican border, linked climate to the flood of US-bound migrants from Central America.

US Speaker of the House Nancy Pelosi, poses for a group photograph with US congress members, including US Representative Alexandria Ocasio-Cortez, during the COP26 UN Climate Change Conference in Glasgow
US Speaker of the House Nancy Pelosi, poses for a group photograph with US congress members, including US Representative Alexandria Ocasio-Cortez, during the COP26 UN Climate Change Conference in Glasgow AFP / Paul ELLIS

In 25 years of working on immigration issues, she said, "I have never before seen so many migrants who are fleeing their homelands because of climate change."

Drought and shifting weather patterns have disrupted rain-fed agriculture, and the region has been devastated by increasingly severe storms and drought.

"If we think that the migrant situation we are seeing in America is bad today, it is going to get become exponentially worse over the next several years," she added.

The arrival of Biden in the White House has helped to restore US credibility in Glasgow, but veteran diplomats at the 196-nation UN talks -- which have dragged on for a quarter century -- remain wary.

"We lost a number of years because of the US withdrawal," said Laurence Tubiana, who helped craft the 2015 Paris climate treaty at France's chief negotiator. "We have to make up for that."

The United States also turned its back in 2001 on the Kyoto Protocol, fatally crippling the treaty, which imposed mandatory carbon pollution cuts on some 40 rich nations.

When asked whether the US had recovered its "moral authority" on climate, Ocasio-Cortez acknowledged the damage done.

"No, we have not," she said. "We have to actually deliver the action in order to get respect and authority internationally."

Passing the Build Back Better act would go a long way towards doing that, she added.

The COP26 negotiations, running through Friday, are tasked with capping global warming at 1.5 degrees Celsius, and providing finance so that developing nations can cope with future impacts and deal with those that have caused devastation.