By Jeff Mason and Valerie Volcovici

GLASGOW (Reuters) – President Joe Biden on Monday will try to assure world leaders that the United States can 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, his top climate aides said.

Biden will join leaders from over 100 countries in Glasgow for the start of the COP26 climate conference, which kicks 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.

National Climate Adviser Gina McCarthy said Biden was committed to delivering on that goal in large part through a key budget bill that would unleash $555 billion in climate spending that 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.”

The House of Representatives has not yet confirmed a date for a vote on the legislation.

McCarthy also addressed concerns around a Supreme Court announcement late 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.

Biden will also announce on Monday a long-term strategy laying out how the U.S. will achieve a longer-term goal of net-zero emissions by 2050 and announce that he will work with 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.

(Reporting by Valerie Volcovici; editing by Diane Craft)