Various environmental groups hailed former Vice President Joe Biden Joe BidenBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Harris faces pivotal moment with Supreme Court battle MORE’s newly released climate plan as “comprehensive” and a “clear vision” after initially knocking reports the plan would focus on “middle ground.”

The Sunrise Movement on Tuesday called Biden’s proposal “a comprehensive climate plan that cites the Green New Deal and names climate change as the greatest challenge facing America and the world.”

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Last month, the youth-led group

knocked reported details

of the forthcoming plan as being “a death sentence for our generation.”

Greenpeace on Tuesday called the plan, which aims to transition the U.S. to net zero emissions by 2050, “A critical step forward for Biden on the climate crisis.”

Just last week, the group had graded Biden’s climate policies with a D-minus. A Greenpeace spokesperson denounced Biden's anticipated plan for being “dangerous and irresponsible.”

The transition from hostility to support marks an important achievement for Biden, who is leading polls as the top Democratic presidential candidate.

Climate change has risen as a leading issue among Democratic voters and Biden’s new plan, which appears to appease many of his harshest climate critics, indicates he is committed to addressing climate change during his campaign and as president.

“We are in a climate emergency and we must take drastic action now to address it,” Biden tweeted when releasing his plan Tuesday morning.

Key differences to Biden’s plan not mentioned in earlier reports include a commitment to rejecting campaign donations from the fossil fuel industry and support for the Green New Deal.

Biden’s campaign has pushed back on earlier characterizations of the forthcoming plan as “middle ground,” saying the specifics released today have always been in the works.

However, the plan, a $5 trillion investment in clean energy, has a much slower trajectory than those of other candidates who have introduced climate policies.

Biden’s plan aims to achieve a 100 percent clean energy economy by 2050. The Green New Deal, championed by Rep. Alexandria Ocasio-Cortez Alexandria Ocasio-CortezWells Fargo CEO issues apology after saying there was a 'limited pool of Black talent' Brand responds to Trump claim protesters throw tuna cans at police: 'Eat em, don't throw em' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context MORE (D-N.Y.) and embraced by other presidential hopefuls including Sens. Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (D-N.J.), Elizabeth Warren Elizabeth WarrenDimon: Wealth tax 'almost impossible to do' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context Democrats shoot down talk of expanding Supreme Court MORE (D-Mass.) and Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I-Vt.), instead calls for a 100 percent renewable electric grid by 2030.

But not every environmental group is satisfied with the slower transition away from fossil fuels.

“Biden’s focus on ‘net zero’ emissions, carbon capture programs, and vague pollution pricing schemes all point to one outcome: a society continuing to be dominated by fossil fuels, and a future of irrevocable climate chaos,” Wenonah Hauter, executive director of Food & Water Action, said in a statement. “The only real way to avoid this perilous future is to transition immediately to a truly clean, renewable energy economy. The way to jumpstart this transition is by banning fracking and halting all new fossil fuel development now.”

Green groups embracing Biden’s plan comes after the pushback many gave to former Texas Rep. Beto O’Rourke when he announced a climate plan in April.

Like Biden’s plan, O’Rourke's called for a $5 trillion investment in renewable energy, and he called for a 2050 timeline.

But unlike Biden, green groups pounced.

“Unfortunately, Beto gets the science wrong and walks back his commitments from earlier this month in Iowa to move to net-zero emissions by 2030,” Varshini Prakash, executive director of the Sunrise Movement, said in a statement.

“Beto claims to support the Green New Deal, but his plan is out of line with the timeline it lays out and the scale of action that scientists say is necessary to take here in the United States to give our generation a livable future,” she said.

Ocasio-Cortez also said the timeline wasn’t fast enough.

“Personally, I think we need to have more aggressive timelines than that to be honest,” she told The Hill in April.

The reasoning for the newfound support of a longer timeline might be tied to inner politics and an acknowledgement by environmental action groups that a harsh attack on a top candidate like Biden could hurt their environmental efforts down the line.

“There are groups for whom he is either their first choice or one of a handful of acceptable choices who don’t want anyone criticizing candidates’ plans,” said an environmental advocacy source. “This plan is vague in many respects. A lot of it is just hand waving at issues. But they rush to say ‘comprehensive.’ ”