The discussion “got a little contentious over the historic merit of fossil fuels,” the mayor, Jeff Katz, told me this week. He and his family were drawn to Cooperstown by its baseball legacy; he has written two books on the topic, including “Split Season,” about the strike-marred 1981 baseball season.

As a former options trader in Chicago, Mr. Katz is also financially sophisticated. He and the trustees oversee a pension fund, with total assets of about $900,000, that benefits the town’s volunteer firefighters and emergency squad. Of that amount, about $140,000 was invested in an S.&.P 500 fund that included fossil fuel stocks. But last year, State Street started an exchange-traded fund that excludes fossil fuels from the S.&P. 500 (the fund’s symbol is SPYX), offering a cost-efficient way to purge fossil fuels from any portfolio.

On Oct. 24, the trustees voted unanimously to move to the nonfossil-fuel ETF.

“It’s something people believe in, and we thought it’s a positive way for the name of Cooperstown to be out there,” the mayor said. “It’s meaningful in that way. It’s not so meaningful financially. We’re not a $100 million pension fund. No one will suffer if Exxon Mobil triples in the next year.”

He added that he and the trustees didn’t realize Cooperstown would be the first community in the nation to divest itself of all fossil fuels.

But the trustees’ decision, and especially Mr. Allstadt’s comments about driving off a cliff, struck a nerve with a village resident, David Russell, who moved with his family to Cooperstown from Westchester County soon after the terrorist attacks of Sept. 11, 2001. Mr. Russell is an asset manager who commutes to Manhattan, but he is also steeped in pension fund management as a former counsel to the New York state comptroller H. Carl McCall, who oversaw the state’s vast public retirement plan.

“It’s a very pristine place up here,” Mr. Russell told me this week. “Feelings run very high about the environment. A lot of people went crazy over fracking.”

“Lou Allstadt went from being a retired oil executive to a pied piper against fossil fuels, which is fine for him personally,” he added. “But as a trustee, you have to look at this through the lens of fiduciary duty, which means acting in the best interest of the beneficiaries. Village trustees shouldn’t be stock pickers, and they shouldn’t be injecting social issues into the decision.”