During a recent virtual fundraiser focused on climate action, former vice president Joe Biden made a direct appeal to voters young enough to be his grandchildren.

“I want young climate activists, young people everywhere, to know: I see you. I hear you. I understand the urgency, and together we can get this done,” said the 77-year-old Democrat, who days earlier had announced a $2 trillion plan to combat climate change and environmental racism — the most ambitious blueprint released by a major party nominee for president.

The moment marked a shift months in the making.

Biden had rolled out a proposal during the primaries — a $1.7 trillion plan that aimed to make the nation carbon neutral by 2050 — that did not impress many young activists who view climate change as an existential crisis.

The youth-led Sunrise Movement gave Biden an “F’ rating, saying his plan lacked detail and paled in comparison to the aggressive action proposed by rivals such as Sen. Bernie Sanders (I-Vt.) and Sen. Elizabeth Warren (D-Mass.), who had embraced the far-reaching Green New Deal.

This spring, with the Democratic nomination locked up, Biden’s campaign faced an imperative challenge: to demonstrate to the liberal wing of the party — including skeptical environmental activists — that he was their guy, that he understood the urgency of the problem and that he would craft a transformative plan to meet the moment.

Over three months, the campaign invited ideas from the young climate crusaders, union officials, environmental justice leaders and former Democratic rivals.

The result was a more aggressive and extensive plan that called for the elimination of carbon pollution from the electric sector by 2035, rejoining the international Paris climate accord and spending $2 trillion over four years to boost renewables and create incentives for more energy-efficient cars, homes and commercial buildings.

“We’ve seen a pretty huge transformation in Biden’s climate plan,” said Varshini Prakash, co-founder and executive director of the Sunrise Movement, which claims more than 10,000 members. While stopping short of a formal endorsement, Sunrise will now campaign for Biden, Prakash said.

“What I’ve seen in the last six to eight weeks is a pretty big transition in upping his ambition and centering environmental justice,” she said.

In recent meetings with donors and volunteers, Biden has repeatedly flagged climate as one of central crises facing the country, along with the coronavirus pandemic, the struggling economy and racial justice.

By elevating climate, Biden is trying to channel the enthusiasm of voters who backed Sanders, as well as Washington Gov. Jay Inslee (D) and executive Tom Steyer, who made saving the planet a centerpiece of their failed primary campaigns.

In addition, Biden hopes to appeal to moderate Republicans who say they, too, are concerned by impacts that scientists say are inevitable in a warming world: rising sea levels, devastating droughts, crippling floods and wildfires and more frequent and costly extreme weather events.

Biden has framed his climate plan as a jobs program, making clear that he is prepared to pour unprecedented resources into transitioning the United States away from fossil fuels as part of the effort to boost an economy battered by the pandemic.

Climate change also presents Biden with one of the most dramatic ways to distinguish himself from President Trump, who has dismissed the science behind climate change, rolled back scores of Obama-era environmental protections, announced U.S. withdrawal from the Paris accord and heavily promoted the fossil fuels linked to rising temperatures.

The Trump campaign, meanwhile, has called Biden a “puppet” of activists who “are plotting to strangle American energy producers, sacrificing millions of good-paying, blue-collar jobs on the altar of their extreme climate agenda.” And the president has insisted that Biden’s plans will kill the economy.

“If these far-left politicians ever get into power, they will demolish not only your industry but the entire U.S. economy,” Trump said Wednesday during a speech in Texas oil country.

The American Petroleum Institute, which represents the oil and gas industry, says Biden’s plan to boost renewable energy will hasten the decline of union jobs as their businesses reel from the coronavirus pandemic.

A poll conducted last summer by The Washington Post and the Kaiser Family Foundation (KFF) found that a growing number of Americans describe climate change as a crisis, and two-thirds said Trump is doing too little to tackle the problem. The poll found that about 8 in 10 Americans say human activity is fueling climate change, and roughly half believe action is urgently needed to avert its worst effects.

Still, climate change has never ranked as a top priority for most voters, and recent polling suggests that many have put the issue further on the back burner amid the turbulence of recent months.

In May, a KFF poll found ­that 33 percent of registered voters nationally said climate change is “very important” in their vote — down 10 percentage points from when the group asked the same question in February. Respondents said the economy, health care, the coronavirus pandemic, taxes and immigration were more important.

In crafting his plan, Biden wanted to win over younger and more liberal voters but also avoid alienating voters in swing states. The plan notably does not ban hydraulic fracturing for natural gas, known as fracking, or rule out nuclear power and other technologies that have divided environmental advocates.

“The campaign is trying to reconcile a combination of demands that no political candidate for president to date has been able to successfully navigate,” said Jason Grumet, president of the Bipartisan Policy Center. “All [Biden] needs to do is blend the ambition of progressives and scientists with the pragmatism of organized labor, the energy industry and moderate Republicans. That’s no easy task.”

As the pandemic raged this spring, Biden asked longtime policy aide Stef Feldman and others to craft a more detailed set of climate proposals.

“That was right around the moment when we were starting to recognize the full depth of the coronavirus, both its health impact and economic impact,” Feldman said in an interview. “And so that required us to scale up with the plans we had since the beginning of the campaign to recognize that we were in a new moment, which really demanded a jobs agenda.”

Biden’s campaign reached out to several key groups: mainstream green organizations, labor unions and environmental justice advocates.

Harold Mitchell, Jr., a former South Carolina lawmaker who has spent decades fighting pollution in communities of color, had toured his native Spartanburg with Inslee and had campaigned for Steyer. But in early April, he got a surprise email from the Biden campaign.

“They asked, ‘What matters?’ I told them, ‘What matters is getting it right,’” said Mitchell, who is now part of a group advising Biden on environmental issues.

Cecilia Martinez, co-founder of the Minneapolis-based Center for Earth, Energy and Democracy, found herself on an hour-long online discussion with Biden this month about environmental racism.

The new Biden plan includes a commitment to invest 40 percent of the clean energy money in historically disadvantaged communities — prompting Martinez to call it “the most innovative and bold plan in a presidential campaign that we’ve seen from an environmental justice standpoint.”

Lonnie Stephenson, head of the International Brotherhood of Electrical Workers, started talking to Biden about energy policy in August. “I said, ‘Truly, nuclear needs to be in the mix,’” said Stephenson, whose union representing about 775,000 current and retired power sector workers endorsed Biden. Stephenson cautioned against the Green New Deal, which he considers “not achievable or realistic.”

Inslee, the former rival, also consulted with Biden, and a small group of Inslee’s former advisers helped to persuade both Biden and congressional Democrats to adopt pieces of Inslee’s far-reaching climate plan.

Biden “recognized this as a unique moment, when you could combine the economic benefit of clean energy with the environmental benefits,” Inslee said in an interview. “He had internalized that. It wasn’t just a talking point.”

He called Biden’s recent proposal “ambitious enough for the moment,” but also realistic enough to win votes in Congress. “This is a real plan that can be executed,” Inslee said. “It’s not a pipe dream or a wish list or a fantasy.”

The campaign also convened a climate task force led by two very different Democratic archetypes: John F. Kerry, the patrician 76-year-old former secretary of state and 2004 presidential nominee, and Alexandria Ocasio-Cortez, the 30-year-old first term congresswoman from a working-class Bronx district who had endorsed Sanders and helped craft the Green New Deal.

Logging on to Zoom each Wednesday for about six weeks, the nine-person panel hammered out an outline of a climate plan designed for broad appeal. The group debated difficult choices, such as whether to support nuclear power or to call for a ban on natural gas fracking.

Despite being the nation’s biggest source of carbon-free electricity, nuclear energy has long drawn concerns about the storage of radioactive waste and the risk of accidents. And more recently, a boom in fracking has fed concerns about how the practice can pollute drinking water while also emitting methane, a potent greenhouse gas.

“There were some people on our side that would have wanted to get rid of all fossil fuels ASAP,” said Catherine Coleman Flowers, a Sanders surrogate on the panel.

Toward the end of the panel’s work, the Biden campaign added Rep. Conor Lamb, a Democrat from a ruby-red stretch of western Pennsylvania, to represent oil and gas workers in the crucial swing state. The task force eventually recommended a clean-energy standard that included both nuclear and gas-fired generation, as long as the latter captures the carbon it emits.

The Sanders camp did secure one big win: A commitment to eliminate carbon emissions from power plants on an accelerated 15-year timeline.

The vice president’s approach also is largely in line with a package from Democrats on the House Select Committee on the Climate Crisis steering the economy toward net-zero emissions by the middle of the century. Two select committee members, Reps. Kathy Castor (D-Fla.) and A. Donald McEachin (D-Va.), served on Biden’s task force.

“It is not coincidental that there are similarities in those plans,” McEachin said.

Even after rolling out his new plan, Biden has continued to face pressure from the left. Last week, more than 100 liberal groups, including Greenpeace, called for the next president to commit to executive actions “to address the systemic inequalities of pollution and the climate crisis.”

Prakash, the Sunrise Movement leader who served as a Sanders surrogate on Biden’s task force, said her group still wants Biden do more to wean the country off fossil fuels.

Meanwhile, environmental advocates have begun to work to elect a candidate who might not have been their first choice, but one who stands in sharp relief to Trump.

Recently, a group that includes the League of Conservation Voters announced an ad campaign across six states. “When it comes to climate change, there’s no comparison,” reads one ad. “Trump denied it. Biden will combat it.”

Michele Roberts, national co-coordinator of the Environmental Justice Health Alliance, was among those consulted about climate by the Biden campaign this spring. She remains cautiously optimistic, both that Biden wins the election and that he actually follows through on his new promises. But she is also thankful that his campaign sought a wide range of voices that have been overlooked in the past.

“Everybody knows that Joe Biden can do a whole bunch of talking. But what he did do was that he also listened,” she said. “We needed that. We needed someone to listen.”

Scott Clement contributed to this report.