By Jeff Mason and Valerie Volcovici

President Joe Biden on Monday sought to assure world leaders the United States would keep its promise to slash greenhouse gas emissions by more than half by the end of the decade, even as the key policies to ensure those reductions remain uncertain.

Biden joined leaders from over 100 countries in Glasgow for the start of the COP26 climate conference, which kicked off on the heels of the G20 summit in Rome that concluded with a statement that urged “meaningful and effective” action on climate change but left huge work for negotiators to ensure an ambitious outcome.

Biden, who succeeded former president Donald Trump in January, acknowledged that the United States had not always led by example on climate change.

“That’s why my administration is working overtime to show that our climate commitment is action, not words,” Biden said.

Trump withdrew the United States from the Paris climate accord; Biden returned it when he took office.

National Climate Adviser Gina McCarthy said Biden was committed to delivering on the U.S. emissions reduction pledge in large part through a key budget bill that would unleash $555 billion in climate spending. That bill awaits a vote in Congress after months of fraught domestic negotiations.

“Here in Glasgow, he’s renewing the United States’ commitment to take swift and decisive action, including through his Build Back Better framework,” McCarthy told reporters.

“It’s the largest investment to combat the climate crisis in American history. And it’s going to let us reduce emissions well over a gigaton – that’s 1 billion metric tons – in 2030.”

Biden said on Sunday that his Build Back Better climate and social spending bill will be voted on sometime this week, “God willing.”

Biden announced a long-term strategy laying out how the United States would achieve a longer-term goal of net-zero emissions by 2050.

In his COP26 remarks, Biden said the world needed to help developing nations in the climate fight.

“Right now we’re still falling short,” he said.

Biden plans to work with the US Congress to launch a $3 billion program in 2024 aimed at helping developing countries adapt to and manage the impacts of climate change through locally led measures.

In a conference call with reporters, McCarthy also addressed concerns around a Supreme Court announcement late on Friday that it would review the Environmental Protection Agency’s authority to regulate greenhouse gas emissions, potentially undermining U.S. climate goals.

“We’re confident that the Supreme Court will confirm what those have before them, which is EPA has not just the right but the authority and responsibility to keep our families and communities safe from pollution,” McCarthy said.