US climate envoy John Kerry at the Major Economies Forum on Energy and Climate in September.
CNN  — 

With just one month to go until a pivotal UN climate change conference in Glasgow, President Joe Biden’s climate agenda is on the line.

The fate of Biden’s ambitious climate promises is wrapped up in a large budget bill that’s stalling in Congress, as moderates and progressives in Biden’s own party disagree on what’s needed.

These negotiations are happening at a critical time: in April, Biden promised the US would slash its carbon emissions in half below 2005 levels by the end of the decade, and the clock is ticking.

“I think if this essentially spins out of control and falls apart, that’s definitely going to be a drag on success at a global level” at the COP conference in Glasgow, Center for American Progress founder and Obama climate adviser John Podesta told CNN.

For months, Biden’s climate envoy John Kerry has been traveling the world, pressuring other countries to raise their climate ambitions and decarbonize faster. That won’t carry any weight unless the US does the same, lawmakers say.

“America is the indispensable nation,” Democratic Sen. Brian Schatz of Hawaii told CNN. “We know without American leadership we can’t succeed.”

The US, the world’s biggest economy and second-largest greenhouse gas emitter, has long been the key player at annual international climate talks, and its relationship with China is typically the make-or-break factor in final language and decisions.

As negotiations in Congress hit a fever pitch, Biden’s top domestic climate adviser Gina McCarthy is increasingly bullish that Biden’s administration can meet its decarbonization goals, even if Congress doesn’t pass major climate provisions.

“We are going to advance our climate and clean energy agenda, and we’re going to do it because there’s many other ways to get to an endgame here,” McCarthy said at a Wednesday event. “There are other ways to get at this in terms of regulatory constraints, other opportunities for investment strategies that really just make it too enticing and economically viable to move forward with clean energy that we know the market will respond to.”

White House climate adviser Gina McCarthy speaks in Washington in April.

A White House spokesperson told CNN that tackling climate change is a “top priority” for Biden, and the administration “is using all the tools in our tool chest to solve it. Full stop.”

Behind the scenes, McCarthy’s team is preparing an action plan for how the US can hit Biden’s emissions goal – a 50 to 52% decrease in fossil-fuel emissions by 2030 – Podesta told CNN. It’s expected to be released before COP and include a number of executive and regulatory actions the White House and agencies have already taken, plus additional steps yet to be announced.

The White House will release a national climate strategy later this year, an administration official confirmed.

McCarthy “believes that’s a viable path, and I’ve expressed my view that without the investments, particularly the tax code support for clean power and clean transportation, I think it’s really tough to get there,” Podesta said.

If the White House does have a Plan B to meet their climate goals if reconciliation fails, Democratic lawmakers haven’t seen it – and they’re skeptical it can actually be done. Several Democratic lawmakers told CNN they haven’t been briefed on how the White House could slash US emissions without major investment in clean energy by Congress.