Ten Democratic candidates will take the stage Wednesday to talk at length about their plans for tackling one of the most politically charged topics concerning liberal voters: climate change.

The CNN forum, which will span at least seven hours, marks the first-ever presidential primary event dedicated exclusively to energy and the environment.

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White House hopefuls will speak for about 40 minutes each, and in doing so, they’ll be battling for the title of top environmental candidate.

The list of candidates comprises 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, former Rep. Beto O’Rourke (D-Texas), businessman 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, 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 (D), former Housing and Urban Development Secretary Julián Castro and Sens. 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-Minn.), 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.), 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 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.).

The event starts at 5 p.m. and is seen as a compromise for Democratic presidential candidates who for months have been calling for a 2020 climate debate.

The Democratic National Committee (DNC) has long opposed the idea of a single-issue debate and has prohibited candidates from participating in any unsanctioned debates, shutting down any chance that the candidates might be able to face each other on stage on this issue. Instead, candidates on Wednesday will talk one-on-one with a CNN moderator and take audience questions.

Roughly 10 minutes of debate time in the past two debates have focused on climate.

Climate change has become a top voting issue among Democrats, according to polls, and Wednesday’s forum could be a chance for candidates to emerge as the next climate candidate — a slot vacated by 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 (D).

Inslee, who released a six-part climate action plan, dropped out of the presidential race in late August after he failed to make the cut for the DNC’s third presidential primary debate, scheduled for Sept. 12.

Many environmentalists say Sanders’s proposal is the most robust.

“Bernie’s plan he just released stands out for both the level of ambition and for the need to tackle economic and racial injustice in this country,” said Lauren Maunus, a policy and political coordinator for the Sunrise Movement, the youth climate action group that helped shape the Green New Deal.

Sanders’s plan and his environmental record also make him the top-rated candidate, according to rankings compiled by Greenpeace.

Other participants waited until the last hour to release comprehensive climate plans. Buttigieg and Harris put forth their own individual climate-focused proposals Wednesday morning, the day of the event.

Booker rolled out a climate plan Tuesday, building upon his earlier environmental justice proposal and setting a 2045 deadline for achieving net-zero emissions.

Booker’s latest proposal boasts a $3 trillion investment spread over a number of areas, including $400 million in clean energy research, $100 billion to promote conservation farming practices, and $50 billion for an environmental justice fund that could be used to get lead out of water and clean up hazardous waste sites.

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Castro also unveiled the first portions of his climate plan on Tuesday, which would decarbonize the U.S. economy by 2045. The plan also includes many elements considered part of the Green New Deal, such as universal health care and a $15 minimum wage. His campaign said three more climate proposals are forthcoming.

Castro previously proposed a civil rights bill for environmental issues, including more legal mechanisms for going after polluters whose actions disproportionately hurt communities of color.

Warren announced Tuesday evening she would be adopting Inslee's overarching climate plan. While Warren had previously released various policy proposals focusing on specific issues related to climate, adopting Inslee's plan gifts her with a robust climate policy going into Wednesday's forum.

Many of the 2020 Democratic presidential candidates will also appear at a climate forum hosted by MSNBC later this month.

This post was updated 8/4/19