Students, faculty and alumni at Harvard University celebrated Earth Day on Monday by calling on the university to eliminate oil and gas companies from its $40 billion endowment. The divestment campaign is raising the alarm over the impact fossil fuels are having on the climate.

"We believe it is morally unjustifiable to invest in the industry at the heart of the climate crisis," said student organizer Ilana Cohen. "We fight because we reject the hypocrisy of a university that refuses to align its financial principles with its ethical ones."

"Fossil fuels have been the energy that we have used since hominids came on this earth, but we do not need to be Neanderthals in terms of understanding what we need to do moving forward," said former EPA Administrator Gina McCarthy, who's now on the faculty at the Harvard T.H. Chan School of Public Health. "So let's invest where our health is. Let's invest where justice belongs. Let's invest in the future, not the past."

Former Harvard Overseer and former U.S. Sen. from Colorado Timothy Wirth expressed confidence that the divestment is going to happen, even if it takes a while.

"The message should go to the university that we're not going away," Wirth said. "We're going to be here for a prolonged period of time, until this policy is changed and Harvard assumes the leadership role that it should sustain and maintain, as it has for a long period of time."

The university refused to drop fossil fuel companies from its endowment investments after a similar call in 2013. But student Ilana Cohen says this time will be different.

"The political moment is different right now," Cohen said, pointing to youth activism on the subject around the globe, including student "climate strikes" and recent "extinction rebellion" protests in London. "There is a clear and palpable need for climate action, and we are making that heard."

Harvard's response to the demand is consistent with what the university said in 2013.

"The University’s position, as it has stated previously, is that it should not use the endowment to achieve political ends, or particular policy ends," Harvard spokesman Jonathan Swain said in a written statement Monday. "There are other ways the University works to influence public policy, including through scholarship and research."

Specifically, Swain pointed to research funded by the university's Climate Change Solutions Fund and its commitment to the UN-sponsoredPrinciples for Responsible Investment.

But this would not be the first time the university dropped some investments for a social reason.

"Harvard divested four times in the last 40 years," said Harvard Professor James Engell. "Once from companies wholly owned by South African firms, once from firms doing business in South Africa, once from big tobacco, and once from companies complicit in violating human rights in Dafur."

Craig Altemose, a Harvard alum and head of the Better Future Project, which is coordinating divestment programs around the country, said in those decisions related to South African apartheid, Harvard didn't actually lead on the issue.

"Harvard ultimately did divest, but they were one of the last universities to do so, and had very little impact," Altemose said. "So they really got no credit. When Nelson Mandela came to Massachusetts, he did not credit Harvard for leading. Harvard was a very late follower."

When it comes to climate-related divestment, though, Altemose says, Harvard has the opportunity to be a leader.

The student group leading the campaign, Harvard Undergraduates for Environmental Justice, has organized a week of events on the subject culminating in a rally on Harvard Yard on Friday afternoon.