In a voters guide released Thursday ranking all 2020 presidential primary candidates by their plans to address the climate emergency, Sens. Bernie Sanders and Elizabeth Warren tied for the highest spot—beating the other top-tier candidate, former Vice President Joe Biden, by 25 points.

"The difference between climate calculations for Elizabeth Warren, Bernie Sanders, and Joe Biden comes partially from Biden's failure to advocate for 100 percent renewable energy by 2030."

—Karyn Strickler, Vote Climate U.S. PAC

The scorecard, published by Vote Climate U.S. PAC, gave each candidate a score between zero and 100 based on their position on whether climate change is real and human-made, climate action platform, leadership on relevant issues, and stance on a carbon fee. Each candidate also got an overall score.

Sanders (I-Vt.) and Warren (D-Mass.) were joined by fellow Democratic presidential primary candidates Sen. Cory Booker (D-N.J.) and billionaire activist Tom Steyer at the top; all four received an overall score of 93.75. Biden and former Texas Congressman Beto O'Rourke scored the lowest among Democrats at 68.75.

Although the Democratic field remains crowded, recent national polling has shown Biden, Warren, and Sanders as the top three contenders by a wide margin. Vote Climate U.S. PAC president Karyn Strickler explained in a statement Thursday that "the difference between climate calculations for Elizabeth Warren, Bernie Sanders, and Joe Biden comes partially from Biden's failure to advocate for 100 percent renewable energy by 2030."

"In his climate plan Biden calls for a 100 percent clean energy economy and net-zero emissions by no later than 2050," Strickler noted. "Among other things, we score candidates on their plan to keep fossil fuels in the ground. Vice President Biden supports ending fossil fuel subsidies and ending fossil fuel extraction on public lands, as does Sanders and Warren. But Biden signed the No Fossil Fuel Money Pledge and subsequently violated that pledge by attending a fundraising event co-hosted by Western LNG's co-founder Andrew Goldman."

RELEASED TODAY: Vote Climate U.S. PAC's 2020 Presidential voters guide https://t.co/WzQDdolePp showing a huge divide among Democratic POTUS frontrunners. pic.twitter.com/cb2ZiEukVo — Vote Climate US PAC (@VoteClimateUS) September 26, 2019

Strickler said that "no presidential candidate received an overall climate calculation of 100 because all three frontrunners for the Democratic nomination need to improve their climate calculations in the 'carbon fee' category. Warren, Sanders, and Biden all support a fee on carbon pollution, but all three score 75 on carbon fee, due to their need to become powerful advocates and strong voices on that issue."

Vote Climate U.S. PAC gave the three Republicans challenging President Donald Trump scores of 25 or lower. Trump, who has spent his time in office rolling back dozens of climate and environmental regulations, received the lowest score: zero.

The group's statement Thursday said that next year it will release climate ratings for all U.S. House and Senate incumbents and challengers. Vote Climate U.S. PAC is not the only group to evaluate 2020 candidates' climate plans. Greenpeace released a scorecard in May and has updated it as positions have changed and some candidates have left the race.

Greenpeace ranks candidates based on whether they say #NoToFossilFuels and champion a Green New Deal. Currently, Sanders tops that scorecard with an A rating. He is followed by Warren and Booker, who both have an A- score. The next three, tied with a B+, are Steyer, Sen. Kamala Harris (D-Calif.), and Biden.

Several candidates put out new climate plans ahead of a CNN climate forum earlier this month, prompting Greenpeace to update its rankings. In a statement announcing that update, Greenpeace USA senior climate campaigner Jack Shapiro said, "At the end of the day, the real question to ask is: who is willing to use all the tools of the federal government to invest in an unprecedented but absolutely necessary transformation away from fossil fuels to an equitable and 100% renewable future?"