Sitting under a soaring ornamental ceiling in a museum near the Seine, Gov. Jerry Brown gave thanks for the political backdrop that has enabled California’s tougher environmental rules.

“If it weren’t for sympathetic legislators, and powerful constituencies, then California wouldn’t be where it is today,” he said during a Monday event.

One of those powerful constituencies was next to him on stage: Tom Steyer, the environmental activist, former hedge fund manager and deep-pocketed Democratic donor. The U.N. summit on climate change has showcased his political influence, and it has provided him with a new platform for pushing clean energy policies.

Besides his onstage discussion with the governor, Steyer, 58, has led a panel of California business leaders and spoken at the conference center where negotiators are working on an international climate accord.

On Tuesday morning, the billionaire who flew first class to Paris sat in the downstairs lobby of a luxury hotel drinking coffee out of a paper cup and wearing pants frayed at the cuff.

“There is something that has to get done here,” he said in an interview. “This is an opportunity for people in California to try to make the case for the way that we’ve done things.”

Steyer’s access to top California Democrats – he is also close with Senate leader Kevin de León of Los Angeles – has rubbed his political opponents the wrong way. And he has made himself a national player, pumping $74 million into the 2014 midterm elections.

Despite the heavy spending, he rejected any comparison to rich Republican donors such as the Koch brothers, who have used their fortunes to swing campaigns in their favor.

“We’re doing something we think is good for everyone, and we have no self-interest in it,” Steyer said.

Brown, in an interview before the trip, said Steyer’s wealth made him more influential than “if he was homeless down on Spring Street.” But he said his role is “a businessman who is very active on climate change,” making him “highly unusual.”

“Most people are not knocking on my door saying, ‘do more on climate change,’” he said.

Steyer’s efforts have not received a warm welcome by some in the state’s business community.

“We have grave concerns about his lack of understanding about how it’s going to impact the 98% of the economy that is not clean jobs,” said Rob Lapsley, president of the California Business Roundtable, which represents some of the state’s largest companies.

It’s an argument Steyer has pushed back against vigorously, pitching his activities in Paris as an opportunity to tout California’s combination of fighting climate change and growing the economy. With Brown’s help, he gathered state business leaders in the French capital to help make the case, and one by one they praised the policies Steyer has supported.

“There are still people out there who are fighting this,” Steyer said. “We have tons of analysis that says they’re wrong.”

Although Steyer sees a connection between California’s environmentalism and job growth, he said there isn’t a correlation to the state’s high poverty rate.

Boosting renewable energy and increasing the energy efficiency of buildings – two targets signed into law by Brown in October – means “we’re going to end up with a lot of green jobs,” Steyer said.

“Those are physical jobs for human beings,” he said.

Despite the excitement of the Paris summit, Steyer said he is eager to return to the Bay Area later this week.

“I’m always counting the hours to get home,” he said.

Steyer has plenty going on back in California, and on more issues than just climate change. He is working on a commission to study income inequality and support minimum wage increases and is funding a ballot initiative for a $2-per-pack tax on cigarettes.

Steyer declined to run for Barbara Boxer’s U.S. Senate seat in 2016, and now he’s being talked about as a potential gubernatorial candidate.

He said he has not made any decisions about running for governor. Instead, Steyer said, he is focused on next year’s presidential election and is using that to push a national conversation about clean energy.

“All the people I work with think that I am off the reservation,” he said, “but I’m extremely optimistic about where we are.”