The Colorado Sierra Club threw its weight behind Democrat Jared Polis in the four-way gubernatorial primary on Thursday, citing the five-term congressman’s record on environmental and climate change policy and his pledge to move the state toward 100-percent renewable energy sources over the next two decades.

The environmental group, which counts more than 100,000 members and supporters in the state, has said it plans to pour resources into flipping the state Senate from Republican control and electing an ally to the governor’s mansion.

Polis is facing a primary against former State Treasurer Cary Kennedy, who won top-line designation at the Democrats’ state assembly last weekend, and former state Sen. Mike Johnston, who successfully petitioned onto the ballot. A fourth candidate, Lt. Gov. Donna Lynne, is awaiting word whether she submitted enough petition signatures.

The Sierra Club endorsement, Polis told Colorado Politics, isn’t just politically important – it’s personal.

“I love exploring, enjoying and protecting the planet, and that is what Sierra Club is all about,” Polis said in an interview Thursday. “From my hikes and social events over the years to our substantive policy work nationally and at the state level and getting to a renewable-energy future, I’m really excited to be working with Sierra Club, which has always pushed the envelope for climate, for renewable energy, for sustainability.”

In a release announcing the endorsement, Polis’ campaign pointed to his work in Congress to cut subsidies for fossil fuel producers, propose designating 90,000 acres of Colorado wilderness, defend Obama-era methane regulations and protect sage grouse habitat.

“Jared Polis has proven that he will reject the ploys of big polluters and fight to protect our environment and the health of American families,” said Sierra Club President Loren Blackford in a statement. “The Sierra Club will proudly mobilize our members to elect Jared as Colorado’s next governor.”

The Sierra Club didn’t make an endorsement the last time Colorado voters elected a governor, when Democrat John Hickenlooper defeated Republican nominee Bob Beauprez to win a second term. Hickenlooper, who ran on what the Sierra Club describes as “a fairly moderate platform,” is term-limited.

A recent poll conducted by the Sierra Club showed high support among Colorado voters for politicians who support aggressive policies to move the state to all-renewable energy sources over the next 12 years. The poll, released in March, said 68 percent of registered Colorado voters support setting a 100-percent “clean energy” goal by 2030, and 59 percent said they would favor candidates who support that policy.

As far as the 100-percent renewable policy, Polis and Johnston have articulated nearly identical proposals, both involving moving the state there by 2040. Kennedy supports the goal but hasn’t laid out the same timetable – one skeptics point out extends at least 15 years after the next governor would be out of office.

Conservative opponents of the proposal calculate it’ll cost around $45 billion and charge Polis with “making pie-in-the-sky promises to his base without taking accountability for the consequences.” But Polis responds that his critics aren’t basing their cost assumptions on his actual proposals, which involve encouraging markets to accelerate the transition away from fossil fuels and toward clean energy.