In far-flung corners of the federal government, staffers have been busy calculating how quickly the United States could embrace electric cars or phase out the last of the nation’s coal-fired power plants. They are estimating how fast the country can construct new battery-charging stations and wind turbines, as well as how farmers can store more carbon in the soil — and how much Congress might allocate to fund such efforts.

They’re urgently trying to tally up the elements of a major promise, one that could shape how aggressively the world takes on climate change.

By April 22, when President Biden convenes world leaders for an Earth Day summit, he is expected to unveil a new, aggressive plan to cut U.S. greenhouse gas emissions between now and 2030. The moment is aimed at reestablishing American leadership in the fight to limit the Earth’s warming to no more than 1.5 degrees Celsius compared with preindustrial levels — a threshold beyond which scientists predict irreversible environmental damage.

As he crafts the much-anticipated pledge, Biden is facing conflicting political pressures at home and abroad.

A sizable chunk of the Democratic Party’s base and climate activists who helped elect Biden — and a chorus of scientists — want the United States to take bold action to slash emissions at least in half by the end of this decade, compared with 2005 levels. They argue that’s critical to pressure other major economies to follow suit and to help the world avoid catastrophe.

But many Republicans warn that societal changes needed to cut emissions so quickly could harm an already battered economy, particularly in communities closely tied to the fossil fuel industry. And they are poised to campaign against such a plan in the midterms against vulnerable Democrats in swing states, despite Biden’s argument that the shift to cleaner energies and less pollution will create a flurry of new jobs.

As Biden walks that political tightrope at home, leaders around the world have been clear that they expect the United States to step up after four years of the Trump administration disparaging global efforts to fight climate change.

“It’s a moment of truth for the Paris agreement,” said Laurence Tubiana, chief executive of the European Climate Foundation and an architect of the 2015 international accord to cut greenhouse gases. President Donald Trump had withdrawn the United States from the pact; Biden rejoined the agreement this year. “We need a boost, and I do think that the U.S. announcement will be that boost.”

But any commitments the United States makes must also be attainable, she said. “Nobody will be satisfied with good targets without anything backing it up.”

Rachel Cleetus, a policy director at the Union for Concerned Scientists, said making an aggressive pledge to cut emissions at home is the “single biggest and important thing” the United States can do to convince other countries that are heavy polluters to arrive at a key United Nations climate conference in Scotland this fall with their own ambitious plans.

“It is a very, very consequential year,” Cleetus told reporters on a recent call, noting that the world remains woefully off target in its push to limit global warming.

At the same time, Biden officials are keenly aware that promising too much, too quickly could mean relying upon questionable assumptions — specifically, what Congress is willing to fund and what policies future administrations pursue.

“It can’t be something completely unrealistic, or it will have no credibility,” said Jason Bordoff, a former Obama White House official who directs Columbia University’s Center on Global Energy Policy. “We have to have near-term promises that matter.”

Biden campaigned on a promise to fight the “existential threat” of global warming by putting the nation on a path toward net-zero emissions no later than 2050 and to eliminate greenhouse gas pollution from the electricity sector by 2035. In his first months, he has paused new oil and gas leasing on public lands, advocated for moving the government toward a clean vehicle fleet and promised to increase conservation. His administration also is pushing for a massive infrastructure bill that would fund projects essential to accelerate the shift to cleaner forms of energy.

White House national climate adviser Gina McCarthy, who is leading an interagency task force, said in an interview that the Biden administration will craft “a very defensible, analytically solid” blueprint.

But making the math work is not easy.

White House officials have ordered agencies across the government to scour their portfolios for tools to help curb emissions in the years to come. In many instances, the analyses will assume that any new regulations won’t be reversed by a future administration or the courts — even though Trump did dismantle several key Obama administration climate policies.

The upcoming national pledge will be built on the expectation that Congress adopts a recovery package with major federal funding for clean energy projects, according to two people briefed on the matter who spoke on the condition of anonymity because no announcement had been made. That plan is expected to include $60 billion for green transit projects and $46 billion for climate-related research and development, along with installing electric-vehicle charging stations across the country. But the bill’s passage is far from assured, given Democrats’ razor-thin majorities in both chambers.

For now, departments are looking for what steps they already have authority to take to reduce climate pollution, and at the possibilities offered by technological breakthroughs.

“We’re going sector by sector, and what we’re finding is in every sector, there are steep technology learning curves that have moved along in the last five to 10 years,” Ali Zaidi, the White House deputy national climate adviser, said in a recent interview. “We’ve got a really remarkable moment in front of us where the technology is there. Capital has the risk appetite to deploy it. State and local governments have moved us to a better field position today than we were at four or eight years ago.

The scramble to find ways to cut the nation’s carbon output spans nearly every federal agency, in policies that touch nearly every corner of American society — from banking to building codes to the efficiency of home appliances.

The Interior Department is already working to speed offshore wind development, for example, and will pursue stricter curbs on methane emissions from oil and gas drilling operations that were reversed under Trump. Since methane is a powerful but short-lived pollutant, compared with carbon dioxide, it’s an attractive target for the Biden administration as it eyes cuts it can lock in by 2030.

White House officials are negotiating with U.S. automakers to see whether they can reach a deal along the lines of what California struck with four manufacturers back in 2019, imposing stricter tailpipe emissions on cars and light trucks through model year 2026. If they can do it by the April summit, it will add heft to any projection the administration makes on declining carbon emissions from the passenger vehicle fleet.

And at the Agriculture Department, top officials are looking at how they can leverage existing conservation funding to encourage farmers and ranchers to use techniques that absorb carbon and lock it in the land. The USDA also is poised to fund large-scale forest restoration, which would absorb carbon from the atmosphere and store it in trees and soil.

Some environmentalists such as Dominick DellaSala, chief scientist with the Earth Island Institute’s Wild Heritage project, are lobbying Agriculture Secretary Tom Vilsack to create a “natural strategic carbon reserve” by putting all older, carbon-rich forests off limits to logging. If those forests, spanning about 50 million acres, were cut, DellaSala estimates, they ultimately would release carbon seven times greater than America’s annual output.

“Forests will buy us time to get to a carbon-negative economy, since that’s where we need to go,” DellaSala said.

Obama administration officials went through a similar process in 2014, when they spent nearly a year crunching numbers before making a joint climate announcement with China aimed at securing a meaningful global deal the following year in Paris. The United States ultimately pledged to cut its emissions by between 26 and 28 percent, using only executive actions and reductions that state and local governments had written into law.

“We didn’t start with a number. We went from the bottom and worked upwards,” said John Podesta, who oversaw the process as White House senior counselor and worked with agencies to devise a target. “We would say, ‘That’s not enough,’ and then they found more reductions. But that was a rigorous process. They didn’t make it up.”

Some of the same aides who devised the U.S. climate target under Obama — including Rick Duke, who crunched the numbers for the White House in 2014 and now works for the U.S. special presidential envoy on climate, John F. Kerry — have returned under Biden.

But they’ve had less than two months to craft a much bolder U.S. pledge.

New Climate Institute analyst Gustavo De Vivero, whose group helps produce the Climate Action Tracker assessing to what extent countries are reducing their greenhouse gas emissions, said in an interview that the United States is largely on track to meet the lower end of its 2025 pledge, cutting emissions by 26 percent. But, he warned, “it needs significant, ambitious policies to drive down emissions in the following five years.”

Most of the near-term climate gains the United States has made have come from the decline of coal, and other sectors will have to curb their emissions to make significant reductions by 2030. The nation needs to invest heavily in clean energy as it spends money to recover from the pandemic, De Vivero said.

“If you rebuild a carbon-dependent future, it will be very difficult to decarbonize the economy later on,” he said.

Other nations are also weighing whether to lift their climate aspirations this year, and by how much. The European Union has pledged to cut net greenhouse gas emissions at least 55 percent by 2030, compared with 1990. Britain has gone even further, vowing a 68 percent cut. The targets set by other large nations such as China, India, Russia and Brazil could dramatically affect whether the world can reach the goals set in Paris almost six years ago.

Whatever pledge Biden unveils, his critics are certain to dissect it.

“We hope that any emissions reduction pledge does not cause more harm than good,” said America’s Power President Michelle Bloodworth, whose group represents the coal industry. She added that any goal should “be conditioned on other countries taking commensurate actions that are enforceable,” given that about 85 percent of global emissions come from outside the United States.

Even electricity groups whose members use a mix of energy sources that include wind and solar cautioned the administration against moving too fast. Joy Ditto, who heads the American Public Power Association and represents publicly owned utilities, described Biden’s plans to eliminate the industry’s carbon footprint by 2035 as a bridge too far.

“We think a more realistic standard would be more of a 2050 carbon-neutral goal,” she said in an interview. “And even that would be hard.”

Sen. Shelley Moore Capito (W.Va.), the ranking Republican on the Senate Environment and Public Works Committee, repeatedly has said that Biden’s aggressive climate actions could kill thousands of jobs in her state and others that still depend on fossil fuel companies.

During a Senate floor debate this month, she called the idea that transition policies can simply create renewable jobs, easily replacing lost jobs in coal and other fossil fuels, “a fantasy world that does not exist.”

Biden has argued that an aggressive push to tackle climate change would not inflict pain on the U.S. economy but rather could help create millions of new jobs in burgeoning industries.

“We view this as something that’s the greatest economic opportunity since the Industrial Revolution,” Kerry said in a recent interview.

For that reason and others, Biden has repeated a refrain from activists and political allies: Go big.

“It’s not like you’re going to get more people on board if you set a lower target for reductions. That’s just not where the debate is,” said Andrew Rosenberg, who directs the Union of Concerned Scientists’ Center for Science and Democracy. “It’s going to be pretty tough to meet the targets, whatever they are. So you might as well be ambitious.”