Then we’d ask about the school’s mission. Perhaps investments in fossil fuel are justified if profits are used for social good, like financial aid programs, which are supported by endowments. But most elite private colleges remain bastions of privilege. Public universities — especially community colleges, which have better track records on access — have a more compelling claim on this defense.

Next, how much would divestment cost? Not much. According to a 2012 report sponsored by the American Petroleum Institute, oil and natural gas constituted merely 2.1 percent of endowment holdings. Some research suggests that endowments would have performed better over the past decade had they excluded fossil-fuel companies.

Finally, how would divestment advance the cause? Defending Western Washington University’s decision to remain invested in fossil fuels, the president, Bruce Shepard, wrote, “Everybody understands that divestment by our foundation would have no material effect on climate change.” More constructive, wrote Ms. Faust, would be to “think about how we might use our voice not to ostracize such companies but to encourage them to be a positive force.” This recalls South African divestment campaigns, when presidents argued universities could exert more leverage if they remained invested. But Nelson Mandela and the South African president, F. W. de Klerk, each cited divestment as influential. Endowments have quadrupled in size since 1990, in real dollars.

Of course, the National Party had the power to end apartheid. Even the most optimistic environmentalist cannot envision fossil-fuel usage ending immediately. “I also find a troubling inconsistency,” wrote Ms. Faust, “in the notion that, as an investor, we should boycott a whole class of companies at the same time that, as individuals and as a community, we are extensively relying on those companies’ products and services for so much of what we do every day.”

It’s a valid point, but if presidents think it relieves them of all duty, they aren’t listening to the distinction students and faculty have drawn between driving corporations out of business and changing their behavior. For fossil-fuel companies don’t just extract and sell energy. They also spend on elections and oppose renewable energy standards. Investment could be contingent on a company’s agreeing to curtail its political spending, report on climate change or include environmental experts on its board. Universities could distinguish among fossil-fuel companies and industries, as Stanford did in divesting from coal.

It’s impossible to imagine that after a fair debate only a handful of universities would choose to do anything. But it’s not a fair debate. Shared governance — students, teachers and administrators making decisions together — is a defining feature of the university. This unique issue is being decided by trustees, who see their responsibility as maximizing returns. Gofossilfree.org has identified only 41 schools with investor responsibility committees, but they are advisory, with authority reserved to the fiduciaries.

Of course, global warming is at bottom a dilemma about the nature of fiduciary duty — about whether that duty is solely to make money or whether we also owe an ethical obligation to endangered species, the inhabitants of low-lying islands and our children. If this debate included more voices, one can’t help but imagine that our universities might construe their obligation more broadly.