But in the wake of California's 2001 energy crisis, Green Mountain abandoned its California operations. The 60 churches that had signed on to Bingham's deal were "disgruntled, to say the least," she wrote in her 2009 book, "Love God, Heal Earth."
Bingham also faced some stray voltage from the pews. "I was criticized when I was first preaching for bringing a political issue into the church," she said.
Because environmental concerns like climate change can seem distant and abstract to congregations, most faith leaders instead focus on issues of more immediate personal concern, said sociologist Laurel Kearns from Drew University in New Jersey, who studies religion's role in environmental activism.
"A lot of folks come to their environmental knowledge separate from the church," Kearns added. "Most of us don't think about the environment in relation to our own personal identities."
Bingham decided to broaden and deepen her mission. She extended it to people of all faiths and set out to get individual congregations involved in the nuts and bolts of reducing their own greenhouse gas emissions. There was, she would remind them, a religious connection.
"The exciting thing about it was that every mainstream religious tradition has a mandate that we are the stewards of creation," Bingham said.
'Cool Congregations' and skeptics
She also stressed the temporal rewards of going green. Lured partly by the prospect of saving on their energy bills, IPL churches found they could lower their carbon footprint by replacing old refrigerators, upgrading air conditioning systems and leasing solar arrays. A Texas synagogue replaced its light bulbs with light-emitting diodes, a Unitarian church in New Mexico installed solar panels on its roof, and hundreds of other churches joined Bingham's movement to become "Cool Congregations."
The orthodoxy among some who study climate issues is that, despite their rhetoric, religious leaders haven't done much to energize voters. NPR recently reported on IPL's efforts but raised doubts about religion's clout. The report cited a Pew survey conducted in 2010 in which only 6 percent of respondents said religion's influence was most important in shaping their opinions on environmental protection.
But Randolph Haluza-DeLay, a sociologist at King's University College in Alberta, dismissed the Pew study, saying he believes IPL works "on the ground level," where it is more likely to have an impact. He said it has the potential to "have a lot of influence." But whether it does, or doesn't, he added, is hard to measure.
Bingham bristled when asked about the skepticism that often surrounds her cause: "If I thought there wasn't hope in mobilizing the religious community, I certainly wouldn't have dedicated my life to the effort," she said. "We do our level best to express to people that this is not about politics."
Pews, preachers and prizes
But Bingham has nothing against making surprising political moves herself. Working with Sen. Pavley in California during the 2002 campaign to regulate vehicle greenhouse gas emissions, she persuaded pastors from around the state to preach about air pollution.
When Bingham discovered that an Assembly member who was undecided about the bill was a regular churchgoer, she made a phone call to the member's pastor. A few months after A.B. 1493 had passed, the Assembly member -- who had voted in favor of the bill -- approached Pavley.
"He said, 'I don't know how you did it, but how did you get my priest to come visit me one on one in my house?'" Pavley recalled. "Sally Bingham's efforts helped to secure the passage of that bill."