“We always appreciate hearing from students about their viewpoints, but Harvard is not considering divesting from companies related to fossil fuels,” Kevin Galvin, a university spokesman, said by e-mail.

Several organizations have been working on some version of a divestment campaign, initially focusing on coal, for more than a year. But the recent escalation has largely been the handiwork of a grass-roots organization, 350.org, that focuses on climate change, and its leader, Bill McKibben, a writer turned advocate. The group’s name is a reference to what some scientists see as a maximum safe level of carbon dioxide in the atmosphere, 350 parts per million. The level is now about 390, an increase of 41 percent since before the Industrial Revolution.

Mr. McKibben is touring the country by bus, speaking at sold-out halls and urging students to begin local divestment initiatives focusing on 200 energy companies. Many of the students attending said they were inspired to do so by an article he wrote over the summer in Rolling Stone magazine, “Global Warming’s Terrifying New Math.”

Speaking recently to an audience at the University of Vermont, Mr. McKibben painted the fossil fuel industry as an enemy that must be defeated, arguing that it had used money and political influence to block climate action in Washington. “This is no different than the tobacco industry — for years, they lied about the dangers of their industry,” Mr. McKibben said.

Eric Wohlschlegel, a spokesman for the American Petroleum Institute, said that continued use of fossil fuels was essential for the country’s economy, but that energy companies were investing heavily in ways to emit less carbon dioxide.

In an interview, Mr. McKibben said he recognized that a rapid transition away from fossil fuels would be exceedingly difficult. But he said strong government policies to limit emissions were long overdue, and were being blocked in part by the political power of the incumbent industry.