The Biden administration is working to salvage its credibility on climate change by shoring up key provisions in a troubled tax-and-spending bill and demonstrating its ability to cut greenhouse gas emissions without the help of Congress.

The rush to write climate legislation as part of a massive budget bill comes ahead of critical United Nations climate talks in Glasgow, Scotland, starting Oct. 31, where Biden and his team plan to push other nations to cut their own emissions. Failure to enact an ambitious set of policies could undermine Biden’s ability to broker a deal aimed at averting catastrophic warming.

Biden’s climate agenda suffered a major blow after a key Democratic senator, Joe Manchin III (W.Va.), expressed opposition to a program to reward electric utilities for switching to renewable energy — and penalize those that don’t. The Clean Electricity Performance Program, or CEPP, aims to accelerate power plants’ transition away from fossil fuels, including coal mined in Manchin’s home state.

Now, White House officials and some of their key allies in the Senate are arguing that the United States can still meet its commitment under the Paris agreement to cut the nation’s carbon output in half by the end of the decade, compared to 2005 levels, through a combination of other executive and legislative action.

“We’re just going to have to work hard on a continuing basis to achieve that goal in this package and what the administration can do,” said Sen. Edward J. Markey (D-Mass.) in an interview.

Biden hopes to use the U.S. pledge to secure more ambitious targets from other major emitters at the U.N. summit, which aims to keep the global temperature rise to 1.5 degrees Celsius (2.7 degrees Fahrenheit) compared to preindustrial levels. The planet has already warmed by 1.2 degrees Celsius.

“The unspoken consensus surrounding the U.N. climate summit is that the Biden administration needs to get its infrastructure bills through Congress unhindered to keep the 1.5 degrees target on the table,” said Chris Venables, head of politics at Green Alliance, a London-based think tank. “Without the U.S. showing it is deadly serious about investing in the clean economy, the diplomatic background music will be critically weakened.”

Frans Berkhout, professor of environment, society and climate at King’s College London, said in an interview that while European officials might be more understanding of the domestic political constraints that Biden faces, Russia and China would probably use any legislative failings to their advantage.

“My view is the international climate policy depends on the relationship and balance between China and the United States,” Berkhout said, adding that Chinese officials could leverage Biden’s struggle back home for “one-upmanship.”

Markey, who spearheaded a climate bill through the House more than a decade ago only to watch it later die in the Democrat-controlled Senate, is hoping to avoid a similar fate this time. “We just have to make sure emissions reductions, jobs and justice are at the heart of any package we pass.”

A new analysis published Tuesday by the Rhodium Group suggests that the nation can achieve that level of emissions reductions without the new power plant proposal — but it will require sweeping executive action by not only the Biden administration but state governments as well.

Congress would still have to enact the other clean energy provisions in the budget bill, the economic research firm said, including the extension of tax breaks for renewable generation, tax credits for electric vehicles and grants for clean energy.

“The U.S. can meet its climate targets without the CEPP,” said Ben King, a senior analyst at the firm. “But it’s pretty difficult.”

Rep. Pramila Jayapal (D-Wash.), who chairs the Congressional Progressive Caucus, said Tuesday that the power plant proposal “is challenging” and she had been checking daily with the measure’s main author, Sen. Tina Smith (D-Minn.) “every couple hours” on “what is the substitute that still brings down carbon emissions.”

“We’re looking at what are the different options for that, so that we can figure out how do we get to the same goal,” she said.

Preparing for the possible defeat of the clean electricity program, the White House is also emphasizing there is more than one way to meet Biden’s climate goal. “The good news is there are a range of good ideas and proposals out there from members of Congress,” White House press secretary Jen Psaki told reporters Monday.

Already during Biden’s first nine months in office, she noted, the Environmental Protection Agency has moved to tighten tailpipe emissions from new cars and curb the use of super-polluting chemicals in refrigerators and air conditioners.

Biden, she said, “has not waited for legislation.”

And the EPA is days away from issuing a major new rule to plug the leaking of methane, a greenhouse gas more powerful than carbon dioxide, from new and existing oil and gas operations.

“We need to lean in and set a very aggressive standard so that the industry understands what the rules of engagement are and what the expectations are,” EPA Administrator Michael Regan said in an interview with The Post this month. “Methane is such a potent pollutant, it’s important that we understand what the contribution is from this industry.”

But some of the biggest potential reductions in U.S. emissions lie in the nation’s power sector. Environmental advocates hope the administration will use the Clean Air Act to cut carbon emissions from power plants, even without the help of Congress.

The EPA is poised to soon bolster that existing authority by restoring the legal foundation for curbing coal plants’ mercury emissions, which was undone under the Trump administration. Limiting mercury, a dangerous neurotoxin, can also cut down on climate pollution released alongside it.

“EPA legally does have many tools” to cut power-plant emissions, said Natural Resources Defense Council senior attorney Emily Davis. She added that the mercury rule, “once we see it, could be one of those tools.”

But it’s a tricky task, given that the Supreme Court once blocked an Obama-era plan to cut greenhouse gas emissions under a Clean Air Act rule.

Even without sweeping regulation, hundreds of U.S. coal plants have shut down over the past decade, due to stiff competition from cheaper natural gas, wind and solar generation.

More recently, the United States has slipped. With tighter gas supplies during the coronavirus pandemic, the use of coal for electricity in the United States is actually expected this year to increase for the first time since 2014, according to a report this week from the U.S. Energy Information Administration.

The most significant remaining climate policy in the reconciliation package is a suite of tax credits to build solar and wind projects and consumers to buy electric vehicles.

“The Finance Committee proposal, which got full support on our side, was always the linchpin of the carbon agenda,” said Sen. Ron Wyden (D-Ore.), who is shepherding the tax package as chair of the Senate Finance Committee.

Yet if the climate provisions get watered down even further, some liberal senators warn they may pull their support. With a razor-thin majorities in both the House and Senate, Democrats can’t afford to lose many votes in their caucus.

“I can’t support a reconciliation bill that doesn’t have a strong climate title, and I think there are a lot of folks who share that belief in the Senate,” Sen. Chris Murphy (D-Conn.) said, without specifying his bottom line.

“I know the administration has been talking more about the potential for executive action to be significantly impactful,” he added. “My current belief is without legislative changes we’re not going to come anywhere close to our Paris agreement [commitment]. But I’m eager to see something from the administration that suggests otherwise.”

Some Democrats have floated the idea of replacing the clean electricity program with a tax on carbon dioxide pollution. But while popular among economists, some Democrats view it as politically explosive.

“I’m not a big fan of the carbon tax,” Sen. Jon Tester (D-Mont.) told reporters Tuesday. “I just don’t think it works in the way it was explained to me.”

Many Democrats and environmental advocates remain intent on forging a deal, given that this may represent the best shot in a generation to pass meaningful climate legislation.

“Would it be different if there were 70 of me in the Senate? Sure,” said Sen. Brian Schatz (D-Hawaii), one of the Senate’s biggest climate hawks, on Monday evening. “But I don’t think we want to catastrophize this thing quite yet.”

Maxine Joselow, Karla Adam and William Booth contributed to this report.