As colleges around the country race to eliminate their greenhouse gas emissions, Waterville’s Colby College has made a major announcement.

Colby is the fourth college in the country to become 100 percent carbon-neutral, a term that means that its net impact on greenhouse gas emissions is zero.

The goal, which was achieved two years ahead of a 2015 target, was the result of decades of actions, with one major boost coming with the recent installation of a biomass plant to heat campus buildings, according to Ruth Jacobs, Colby’s associate director of communications.

The plant, which uses sustainably harvested wood biomass instead of oil, went online in 2012.

“The two major ways (have) been our switch to renewable electricity and our switch to biomass for heating,” she said.

In 2008, Colby President William D. Adams signed the American College and University Presidents’ Climate Commitment, which has been signed by 15 of Maine’s approximately 30 colleges.

The climate commitment is meant to “re-stablilize the Earth’s climate, the defining challenge of the 21st century,” according to the group’s website.

Unity and the University of Maine System’s campuses also have signed the commitment, under which they agree to set and work toward goals including carbon neutrality.

Colby set a goal of 2015 for carbon neutrality, while Unity College set a goal of 2025 and the University of Maine at Farmington set a goal of 2035. Colby buys carbon offsets to negate some of its emissions, which Jacobs said is essentially investing in activities that will work to reduce emissions elsewhere in the world.

“The money from those offsets will help to build and sustain a market for projects in New England that directly affect the impact of human activity on climate change,” Jacobs said.

The actual rate of emissions at Colby in 2013 is projected to be 3.87 metric tons of carbon dioxide for every full-time student. The number might sound like a lot, but it compares favorably to 2012, when the rate was 5.72 tons per student, and even more favorably to 2002, when the number was 15.6 tons per student.

It is also significantly less than a national average of about 9 tons per student.

Matt Hongoltz-Hetling can be contacted at 861-9287 or at:

mhhetling@centralmaine.com