National resolutions aren't legally binding, but most churches end up complying, according to Jim Antal, minister and president of the Massachusetts branch who is leading the effort. The UCC has a national pension fund worth $2.9 billion. Each local church controls its own endowments.

The UCC Pension Boards did not respond to requests for information on how much of its pension is invested in fossil fuels. Antal said UCC churches across the country have reached out to him to pledge their support or learn more about divesting their endowment funds.

Julie Fanselow, a spokesperson for Interfaith Power and Light, a campaign aimed at helping churches address climate change, said she has heard rumblings that religious leaders of several faiths are looking into divestiture, including Episcopalians, Methodists and Presbyterians, among others.

Small at First Parish in Cambridge said his congregation will discuss divesting its roughly $5 million endowment at its investment meeting next month, and said he has talked with several other Unitarian Universalist churches interested in following suit. There are roughly 1,000 Unitarian Universalist churches across the country, which are non-denominational and socially liberal.  

Advocates say divestment is largely symbolic in terms of its ability to affect the fossil fuel industry, but they believe participation of religious institutions could advance their larger cause. Forty percent of Americans—nearly 125 million people—attend religious services every week or almost every week, according to polls.

"Our political system has thus far shown itself incapable of facing this issue," Small said. "Hopefully millions of people taking a stance on this issue through their involvement with religious communities will resonate with politicians."

In his role as president of the Massachusetts Conference of the UCC, Antal said he spends each Sunday preaching at a different church in the state and tries to incorporate climate change into roughly every other sermon.

"The difference in the number of people that take offense or oppose my sermons [about climate change] from seven years ago to now is incredible," he said. "The question has shifted from, 'Is this happening?' to 'What can we do about it?'"