UNITY — Lauded for his work to elevate the status of Unity College, President Stephen Mulkey is stepping down at the end of the year.

Unity College announced Monday that Mulkey will retire on Dec. 31, ending a four-year tenure at the institution, according to a press release from the college.

Mulkey, who was hired in 2011, presided over new initiatives at the college and helped lead the effort to divest the institution’s investments in fossil fuels, making Unity College the first in the nation to take that action.

Bruce Nickerson, chairman of the Unity College board of trustees, said Mulkey made many positive changes to the institution and will leave an impression on the school and community.

“Stephen has not only elevated the profile of our college, but he has built a solid infrastructure, stabilized enrollment while attracting a bright, energetic and engaged student body, made significant gains in fundraising, and implemented visible improvements to our campus,” Nickerson said in a written statement.

Mulkey was traveling Monday and unavailable for comment.

Mulkey became Unity College’s 17th president after leaving the University of Idaho, where he was a professor and director of environmental sciences. He earned his bachelor’s and master’s from the University of Missouri and doctorate from the University of Pennsylvania.

He is known for his research on ecosystems and climate change, which he calls “the greatest challenge of our time in what will come to be known as the environmental century.”

Aside from his leadership during the divestment process, Mulkey led an effort to adopt a sustainability science framework for the college’s curriculum; stewarded a $10 million gift to the college; oversaw the renovation and modernization of teaching and research facilities; and began the construction of two new fossil fuel-free residence halls, which increase the campus footprint by 44,000 square feet, according to information from the college.

“We feel good about him turning the place around and putting us on good footing moving forward,” said Bob Mentzinger, Unity College’s associate director of media relations.

The college is creating a transition plan as Mulkey’s departure nears.

Mentzinger said Mulkey chose to put off his retirement until the end of the year to assist the college in finding his replacement.

The search for a new president will gear up in the fall, Mentzinger said, and Mulkey, the trustees, faculty and staff will work together to find the right candidate to lead the college.

Mentzinger said Mulkey does not plan to become the president of another college.

Mulkey intends to enjoy his retirement in Florida, Mentzinger said, and to pursue his research interests that being the college’s top administrator prevented him from working on.