(CNN) Multiple independent analyses have found President Joe Biden simply can't hit his goal of cutting greenhouse gases by 50% by the end of the decade without the clean energy provisions in Build Back Better, the President's signature economic and climate legislation.
After West Virginia Sen. Joe Manchin torpedoed the bill, experts say these goals are ever more out of reach -- with devastating consequences.
"Without this bill we really don't have a plan to tackle the climate crisis in the US," said Leah Stokes, a senior policy adviser at Evergreen Action and climate expert at the University of California, Santa Barbara. "Cutting carbon pollution 50-52% is a really big goal, it's what's necessary, but it's not going to happen without significant federal investments."
The President in April pledged to slash planet-warming emissions -- mainly carbon dioxide from things like power generation and transportation -- in half by 2030. It was an ambitious goal, but one that climate scientists say is necessary to avoid even worse climate change impacts. Scientists reported this fall that the planet is warming catastrophically, and the expensive and deadly consequences are becoming more severe with every fraction of a degree.
Biden is trying to stem the climate crisis by tackling its cause. But experts CNN spoke to were blunt: Without the bill's clean energy provisions -- especially its $320 billion in flexible 10-year clean energy and electric vehicle tax credits -- Biden's goal is sunk.
"I don't think you can get to 50% by 2030 without any action by Congress," said John Podesta, Obama's former top climate official and the co-founder of liberal think-tank Center for American Progress. "I don't think you can sugarcoat that."
Asked Monday whether the White House was looking at a climate contingency plan with additional executive actions if Build Back Better implodes, White House press secretary Jen Psaki said the administration is "always looking at additional steps we could take."
"There are multiple paths to reaching the President's climate goals," Psaki said. "We have every intention of passing Build Back Better, which includes enormous climate provisions. I would note that there are a number of steps we have taken without legislation, and certainly will continue to build on that."
The Biden administration has taken several executive actions to address the climate crisis, tightening federal regulations on vehicle emissions, hydrofluorocarbons and methane leaks, and announcing the administration would be leveraging its own power of the purse to buy electric vehicles and make federal buildings energy efficient.
But climate experts told CNN Biden must engage Manchin to pass something through Congress to ensure the administration's actions are accompanied by big investments to install wind turbines and solar panels and bring down the cost of electric vehicles and energy-efficient appliances for Americans.
"It's really hard for the President through executive action to take 30% off the cost of every new renewable installation in America for the next decade," John Larsen, director at the nonpartisan Rhodium Group, told CNN. "All of the tax credits, grant programs and other incentives in Build Back Better would make everything else the executive branch has to do easier, as far as getting a handle on greenhouse gas emissions and getting the US on a course to meet its 2030 target."
Rhodium published an analysis in October showing that both the bipartisan infrastructure bill and Democrats' sweeping economic package combined with federal and state regulatory action could get the US close to Biden's 50-52% greenhouse gas reduction goal by 2030. But if nothing was passed through Congress and new regulations were not implemented, greenhouse gas emissions would only fall by 17-25% by 2030. An analysis from Princeton University found similar results.
"It is very unlikely that the whole gap can be filled by state policy and executive action alone," Princeton professor and climate expert Jesse Jenkins told CNN. "Federal policy of this scale and scope is critical."
After an acrimonious display of tension between Manchin and the White House on Sunday, there were signs of hope Monday that a deal could be reached on the climate measures Manchin supports.
Days before Manchin thwarted Build Back Better on Fox News, he proposed a version of the bill that included several hundred billion dollars for climate and clean energy. Manchin and Biden are continuing to talk with a "friendly, constructive" phone call on Monday, CNN reported -- a potentially promising sign for progress in the new year.
But some say the time has come for Biden to wield executive power.
On a Monday call with reporters, Congressional Progressive Caucus Chair Pramila Jayapal said Democrats "should not wait for that legislative path for the President to take action."
"No one should think that we are going to be satisfied with an even smaller package that leaves people behind or refuses to tackle critical issues like climate change," Jayapal told reporters. "That's why it is now incumbent on President Biden to keep his promise to us and to the American people by using the ultimate tool in his toolbox of executive action in every arena immediately."
As a key adviser who oversaw executive action on climate in the Obama administration, Podesta urged caution with Jayapal's approach. Podesta told CNN executive action was enough to help Obama hit a 25% emissions reduction target in his term but said Biden's goal is much bigger and needs Congress to act as well.
"I've a long history of being in favor of taking strong executive action, and I absolutely would encourage the administration to use the whole of government approach," Podesta said, adding that "nothing substitutes" Congress passing a bill.
Executive actions can also quickly be overturned by the next administration -- while legislative investments are more durable.
"These opportunities don't present themselves very often -- the last one was 12 years ago," Larsen said. "Walking away is just going to completely close that window, maybe before it should have been closed."