Ten Democratic presidential contenders will make the case for their respective climate agendas Wednesday when they compete for the title of top environmental candidate.

The seven-hour forum on CNN, with each participant speaking separately, will offer White House hopefuls the chance to emerge as the leading supporter of environmental defense and climate action in the wake of Washington Gov. Jay Inslee Jay Robert InsleeBarr asked prosecutors to explore charging Seattle mayor over protest zone: report Bottom line Oregon senator says Trump's blame on 'forest management' for wildfires is 'just a big and devastating lie' MORE’s withdrawal from the 2020 race. The Democratic governor’s platform was almost exclusively centered on combating climate change.

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“There is definitely now an opening with Inslee not in the race anymore for someone to really step up and kind of be the loudest voice on climate,” said Craig Auster of the League of Conservation Voters.

“What we want to see is plans that match what the science is telling us needs to happen, in terms of the pace and scale,” he added.

Snagging the environmental mantle could help lesser-known candidates distinguish themselves from the crowded field, especially as climate change surges as a key voting issue for Democrats.

“We’re wanting to see what candidates are going to do day one to tackle the climate crisis and how bold they’ll be on climate action,” said Jenny Marienau, political campaign manager with 350.org, a group that advocates for clean energy.

Already, several environmentalists argue that Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) has filled the void left by Inslee’s departure.

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“When it comes to the plans being put out by the candidates, the one plan that I’ve seen that is comprehensive, that is economywide, that meets the demands is the one put forward by Sen. Sanders,” said Mitch Jones, climate and energy program director at Food & Water Action.

“Others have made good points. There are other plans that have components that need to be done,” he said. “But the Sanders plan is the plan that really does set the benchmark. It’s aggressive, but it’s what we need to do.”

Sanders is polling near the top of the Democratic field — often neck and neck with 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.) and behind former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE.

At least eight candidates have come out with climate policy plans, and their contents indicate some common themes are taking shape. Many of the proposals call for specific clean energy targets and wiping out carbon emissions, while several go after polluting industries and clamp down on pathways for the fossil fuel industry to remain viable.

Some candidates also pledged their support for the Green New Deal, a resolution introduced by Rep. Alexandria Ocasio-Cortez Alexandria Ocasio-CortezOn The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline McCarthy says there will be a peaceful transition if Biden wins Anxious Democrats amp up pressure for vote on COVID-19 aid MORE (D-N.Y.) and Sen. Ed Markey Edward (Ed) John MarkeyA game theorist's advice to President Trump on filling the Supreme Court seat Watchdog confirms State Dept. canceled award for journalist who criticized Trump 3 reasons why Biden is misreading the politics of court packing MORE (D-Mass.) earlier this year.

“Even the more moderate candidates were willing to speak quite a bit about investing in renewables, research and development, and the Green New Deal is becoming a consensus position among candidates, which is great,” said Ryan Schleeter, a spokesman for Greenpeace, which ranks candidates’ environmental policies.

“But addressing fossil fuel extraction and fossil fuel imports are what is separating real leaders on climate policy from those that are more in the middle,” he added.

Sanders has targeted the fossil fuel industry in his rhetoric, promising to sue companies in hopes of extracting huge settlements that could help fund his proposed transition to a clean energy economy. He and several of his Democratic rivals argue the industry should pay for years of covering up their knowledge of how fossil fuels impact climate change.

But environmental leaders warn that candidates will need to offer more than just an outline of their ambitious goals.

“Inslee was good at laying out the federal mechanisms for achieving his goals as well as what he would ask of Congress,” Schleeter said, adding that other candidates, including Sanders, haven’t been as good as Inslee at providing those details.

Activists say they will also be keeping an eye on candidates whose climate policies give them pause, such as Silicon Valley executive Andrew Yang Andrew YangBiden's latest small business outreach is just ... awful Doctor who allegedly assaulted Evelyn Yang arrested on federal charges The Hill's Campaign Report: Biden weighs in on police shootings | Who's moderating the debates | Trump trails in post-convention polls MORE.

Yang’s climate plan, unveiled in August, relies heavily on the use of nuclear power to achieve 100 percent clean energy and calls for constructing more reactors. Nuclear energy is a divisive topic in the environmental community, with many opposed to it because of the toxic waste it produces.

“I think Yang’s approach to climate change is deeply problematic,” said Jones, who favors Sanders’s plan and its call to retire all nuclear reactors.

“He’s a tech guy. He’s searching for tech solutions in a way that’s unnecessary."

Yang garnered support from 2 percent of Democratic voters in the most recent Economist/YouGov poll.

CNN said it would invite candidates with at least 2 percent support in four polls approved by the Democratic National Committee (DNC). The window to qualify for the event began on June 28 and ran through Aug. 21.

Biden, Warren, Sanders and Yang will participate in the CNN forum, as will Sens. Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE (D-Calif.), Cory Booker Cory Anthony BookerThe movement to reform animal agriculture has reached a tipping point Watchdog confirms State Dept. canceled award for journalist who criticized Trump 3 reasons why Biden is misreading the politics of court packing MORE (D-N.J.) Amy Klobuchar Amy Klobuchar3 reasons why Biden is misreading the politics of court packing Social media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight MORE (D-M.N.). Former Housing and Urban Development Secretary Julián Castro, South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE and former Rep. Beto O'Rourke Beto O'RourkeJimmy Carter says his son smoked pot with Willie Nelson on White House roof O'Rourke endorses Kennedy for Senate: 'A champion for the values we're most proud of' 2020 Democrats do convention Zoom call MORE (D-Texas) will also participate.

The DNC voted down the idea of hosting a climate debate, but CNN organized the forum in the wake of outcry from environmental groups and voters. MSNBC will host a similar climate-focused forum Sept. 19 and Sept. 20.

Environmentalists say the lengthy CNN event will be an opportunity for those with less developed climate plans to showcase their environmental bonafides.

Harris and Booker have both offered up environmental justice plans but have not unveiled sweeping environmental plans like those from Sanders or Sen. Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (D-N.Y.), who put forth a climate change moonshot plan before she dropped out of the race.

“I think [Harris] has a strong record in the Senate around environmental justice and other climate issues,” said Lauren Maunus, a policy and political coordinator for the Sunrise Movement, the youth climate action group that helped shape the Green New Deal.

But Harris also “has a list of vague priorities on her website,” Maunus argued.

Harris did earn some cred with environmentalists over the summer when she introduced legislation with Ocasio-Cortez that would take the first step toward implementing the Green New Deal.

But activists want to see a comprehensive plan from Harris as well.

She also stirred controversy when she initially planned on skipping the CNN climate forum. Her campaign originally announced that despite qualifying for the event, Harris was booked to attend a fundraiser in California the same night. They later reversed course and rescheduled the fundraiser.

Harris sits has placed fourth in most polls of the Democratic candidates.

Environmentalists say they will also be eyeing Warren, who has released a number of plans that touch on climate issues but not one big climate policy. Warren has 16.5 percent of the Democratic vote according to the RealClearPolitics polling average, just behind Sanders’s 17.1 percent.

Climate change activists credit Warren with being the first candidate to commit to prohibiting new oil and gas leases on public lands, a move that “set off a nice little trend,” Schleeter said. She has also introduced smaller plans that touch on climate and energy goals, including a green manufacturing plan released in June.

Some say the piecemeal approach lays out how climate change has become an issue across several sectors.

“We see it as a deeply intersectional issue,” Marienau said. “At the same time, there are pieces missing from [Warren’s] platform. We’re waiting to hear where she stands on fracking and natural gas.”

Warren’s campaign did not immediately respond to a request for comment.

While observers are keen on hearing more about comprehensive plans, they also stressed the urgency of climate change and how candidates need to highlight what they would do immediately upon taking office.

“I think what we also want to see is candidates saying this is a priority on day one and a priority on the first 100 days of [their] administration,” said Auster.

“We're looking at how candidates are prioritizing this,” he added.