Across the nation, 665 university presidents have committed to eliminating net greenhouse gas emissions from their campuses — but Yale is not among them.

This month, Colby College achieved its objective of going carbon-neutral two years ahead of its 2015 deadline. Colby administrators said that the campus has had a net-zero carbon footprint as of April 4, making it the fourth college nationwide to fulfill the American College and University Presidents’ Climate Commitment. Assistant Director of the Yale Office of Sustainability Melissa Goodall said that by the time the ACUPCC was created in 2007, Yale had already made its 2005 carbon reduction commitment.

“Since Yale already had a climate commitment when the ACUPCC was established, it didn’t really make sense for Yale to shift gears,” Goodall said.

In 2005, Yale committed to reducing its carbon emissions by 43 percent by 2020. Office of Sustainability Project Manager Keri Enright-Kato said that as of 2012, Yale had reduced its carbon emissions to 16 percent below its 2005 level, which she said puts the University on track to reach its 2020 goal. According to the Office of Sustainability’s annual report, this reduction is particularly significant because the campus has also increased in size by 12 percent since 2005.

Enright-Kato said Yale’s strategy for greenhouse gas reduction has focused on reducing the energy intensity of campus buildings, adhering to sustainable construction and renovation standards, and investing in renewable energy technologies on campus. The Office of Sustainability also worked with the University administration to convert Yale’s standard power plant to a cogeneration plant that recaptures the heat lost during the creation of electricity.

The University’s sustainability goal primarily focuses on reducing emissions from purchased electricity for the central and medical campuses, according to the 2012 annual report. As a separate effort, the University is also working to reduce fuel and electric purchases for West Campus and off-campus buildings.

The ACUPCC carbon commitment involves a more significant reduction than Yale’s pledge, but Enright-Kato said she thinks it was designed primarily to catalyze universities that had not previously undertaken sustainability initiatives to make public greenhouse gas commitments.

Colby College Director of Communications Ruth Jacobs said that in pursuing its carbon-neutral goal, Colby employed some strategies similar to Yale’s and also implemented some more large-scale sustainability initiatives. Jacobs said Colby constructed a biomass heating plant that uses wood chips and forest waste to replace the heating oil Colby uses, adding that the plant reduces the amount of oil Colby burns by 1 million gallons annually.

Student leadership was a key factor in pushing for Colby’s carbon reductions, Jacobs said. The Colby Environmental Advisory Committee brings together students, faculty and administrators to devise initiatives that can reduce the school’s greenhouse gas emissions. Jacobs said Colby’s greenhouse gas inventory project was entirely student-led.

“Every major sustainable initiative we’ve done had students at its genesis,” Jacobs said.

Enright-Kato said Yale’s commitment to carbon reduction has been driven primarily by University President Richard Levin, adding that she is confident that the University’s commitment to sustainability will remain under President-elect Peter Salovey’s administration.

Cornell University is currently the only Ivy League University that has joined the ACUPCC.