An activist for the Sunrise Movement knocked former Vice President Joe Biden Joe BidenBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Joe Biden should enact critical government reforms if he wins MORE over his climate plan, even though the youth-led group praised the proposal following its release in June.

Lauren Maunus said Friday that the top White House contender's plan lacks a sense of urgency and fails to produce concrete solutions to addressing the environmental crisis.

“Joe Biden’s plan has a lot of good goals,” Maunus, a policy and political coordinator for the group, told Hill.TV. “Most of the words and rhetoric are in line with what we’re calling for.”

“But he does not back it up with any level of urgency or ambition,” she added, arguing that it lacks “concrete policy goals of how he’s going to achieve that vision.”

A spokesperson for the Biden campaign declined to comment on Maunus's remarks.

The former Vice President scored a 42 percent in the youth-led groups new ranking of top-tier presidential candidates on their support for the Green New Deal. White House contenders Sen. Bernie Sanders Bernie SandersTrump, Biden will not shake hands at first debate due to COVID-19 Sanders tells Maher 'there will be a number of plans' to remove Trump if he loses Sirota reacts to report of harassment, doxing by Harris supporters MORE (I-Vt) came in first at 92 percent, while Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) trailed at 82 percent.

Biden’s $5 trillion climate plan, released in June, channels aspects of the Green New Deal, and aims to transition the U.S. to net zero emissions by 2050. Green New Deal proposals that have been championed by other presidential hopefuls, such as Elizabeth Warren (D-Mass.) and Bernie Sanders (I-Vt.), instead call for a 100 percent renewable electric grid by 2030.

Despite criticizing reported details of the plan prior to its release, the Sunrise Movement hailed Biden’s proposal as providing a “comprehensive” solution to climate change.

Since then, the former vice president and the Sunrise Movement have clashed on other issues. When confronted by a Sunrise Movement activist in October over his decision to open the door to accepting super PAC money, Biden responded, “Look at my record, child. Look at my record." The group later admonished the former vice president, characterizing his response as “frustrated condescension.”

"It's one thing to say 'look at my record,'" said Stephen O'Hanlon, a co-founder and spokesman for the Sunrise Movement told The Washington Post following the exchange. "But we need a president who is putting out a bold vision for this crisis."

Overall, Biden's climate plan has been met with a mix of criticism and praise from various environmental groups. While Greenpeace called the plan a “critical step forward,” other groups like Food & Water Action have criticized its slower timetable for transitioning away from fossil fuels.

Climate change has been among the top issues in the Democratic primary race, and is likely to come up in the Dec. 19 debate.

Updated at 2:18 p.m.

—Tess Bonn