As sustainability becomes a catchphrase on college campuses, 74 presidents of schools from around the country have committed their institutions to climate neutrality. But Yale is not among them.

Last week, the American College and University Presidents Climate Commitment, which is still in the initial phases of its launch, received its 70th signature. The signatories have committed themselves to assessing energy use on their campuses and laying out formal plans to become completely climate-neutral by eliminating greenhouse gas emissions. Although Yale is widely regarded as a world leader in sustainability in higher education, the University has refrained from mapping out plans to reduce emissions beyond 2020.

The Yale administration has not signed on to the agreement or made any commitments beyond 2020 because it is unclear what technologies will be available to reduce fossil fuel emissions further in the future, University President Richard Levin said. Levin announced in October 2005 that Yale would reduce emissions to 10 percent below 1990 levels by 2020, and made headlines when he re-stated this goal at the World Economic Forum in Davos, Switzerland, last month.

Despite this commitment, students and sustainability experts have called for Yale to make a longer-term commitment. Even though any plans to reduce emissions after 2020 would be contingent on the development of new technologies, it is up to universities to create a market for these technologies and to set the bar for other organizations by having ambitious goals, said Anthony Cortese, the president of Second Nature, a nonprofit that works to promote sustainability in higher education. He is also an organizer of the Presidents Climate Commitment.

“If enough companies, enough states, enough colleges and universities, say ‘We are going to try our hardest to get there,’ then that will create pressure,” Cortese said.

Cortese is also a co-founder of the Association for the Advancement of Sustainability in Higher Education, of which Yale is a member.

The Yale Student Environmental Coalition is also pressing Yale to look further ahead than 2020. In a petition jointly sponsored by the Yale College Council, YSEC urged Levin to commit Yale to decreasing its carbon footprint to 80 percent below 1990 levels by 2050. The petition, which has been circulated on paper and on the YCC Web site, has more than 800 signatures.

“We are asking them, essentially, to set a goal that they don’t know they can reach,” YSEC Co-President Micah Zeigler ’08 said. “We believe that [with] Yale, with its vast amount of academic, administrative and financial resources, using these resources, we can innovate in order to reach that goal.”

The University of Pennsylvania is currently the only Ivy League school that has signed onto the climate pledge. Cortese said he hopes to have 200 presidents on board when the commitment is publicly launched in June.