Yahoo did it. So did the presidential campaigns of John Edwards and Hillary Clinton.

Even Norway and Sweden did it. (Europe, not Oxford County.)

Now the University of Maine System, or nearly all of it, has taken the pledge to try to eliminate its contribution to global warming.

The goal is called becoming climate neutral or carbon neutral, because scientists say carbon dioxide emissions are the primary way college campuses, businesses, countries and the rest of us are doing our part to heat up the atmosphere.

Colleges around the country are joining the trend as part of the whole “green campus” movement. They say their efforts reflect the schools’ role in society and their responsibility to the young people they serve.

It’s also a point of competition for the schools to present the greenest reputation to prospective students and alumni.

Dudley Greeley, the sustainability office director at the University of Southern Maine, said Maine’s was one of the first state university systems to sign the American College and University Presidents Climate Commitment. Actually, the presidents of the system’s largest six campuses have signed. The Augusta campus hasn’t made the list yet. One of the signers is USM President Richard Pattenaude, the man who soon will be chancellor of the whole system and who is a strong supporter of the sustainability movement.

Maine’s first school to join the neutrality quest was the College of the Atlantic in Bar Harbor. President David Hales made the pledge publicly last fall.

Also signed onto the Climate Commitment in Maine are Bates and Unity colleges. Bowdoin and Colby, though not officially signed on, have active sustainability programs.

The formal pledge doesn’t come with a deadline for achieving climate neutrality. It does set interim deadlines to meet along the way: Complete an emissions inventory within one year and, within two, create a detailed plan and set a target date for reaching the goal.

Schools have begun by building more energy-efficient buildings, encouraging public transportation, buying power from renewable energy and making other changes.

Energy efficiency and public transportation seem innocent enough, right? There is some controversy around the whole climate-neutral trend, however.

That’s because it’s impossible at this point for a school or a business to produce no carbon dioxide. Employees and students drive cars and fly in airplanes, to name a couple reasons.

A theoretical zero impact requires buying offsets, which are payments to remove an equivalent amount of carbon from the atmosphere somewhere else in the world by planting trees, building windmills or something like that.

Offsets have gotten a lot of scrutiny and criticism because they’re unregulated and somewhat risky. Many also see them as an indulgence or a way to avoid real emissions reductions.

According to Greeley, the campus pledge initiative limits the use of offsets to a fraction of the other reductions that schools have to make. Neutrality, for now, is simply a goal.

So prospective college students now have another question to ask: Is the campus going climate-neutral? If the reply is to go ahead and open a window, that would be a “no.”

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