As the class of 2012 heads off to university this fall and new high-school seniors start the admissions process, some may wonder if their college of choice fits with their own environmental ideals.

Recently, the Princeton Review added a green rating to its annual ranking of the best colleges. This score measures how “environmentally friendly, responsible, and committed the institutions are.”

The schools that scored 99 (out of 100) are:

• Arizona State University, Tempe
• Bates College
• Binghamton University
• College of the Atlantic
• Emory University
• Georgia Institute of Technology
• Harvard University
• University of New Hampshire
• University of Oregon
• University of Washington
• Yale University

The complete list is in the 2009 editions of three Princeton Review college books.

But what really makes for a “green college”? Different organizations have their own criteria, so if the environment is an important factor in where you’ll be spending the next four+ years (and a boatload of money), compare lists and do more research.

For two years, the independent Sustainable Endowments Institute has published a Green Report Card. The full report is available as a PDF online, and it evaluates 200 public and private universities.

The Green Report Card looks at more than just green buildings and recycling. It asks how the schools are using their substantial endowments to support sustainable efforts and fight climate change.

Overall college sustainability leaders on the report card include:

• Carleton College
• Dartmouth College
• Harvard University
• Middlebury College
• University of Washington
• University of Virginia

Check out the complete report card for more high-ranking green schools.

And then there are more subjective lists, like the Daily Green’s top 10 colleges, Grist’s 15 greenest colleges, the Sierra Club’s 10 cool schools, and Campus Corner’s greenest college towns.

You’ll see some overlap in all these rankings. For example, everybody loves Harvard’s green campus initiatives, and how can the tiny College of the Atlantic go wrong with a 100% focus on human ecology and sustainability?

But lesser-known schools and not-obviously green schools are looking to reduce their carbon footprint too. Over 550 university presidents have signed on to the American College and University Presidents Climate Commitment, which pledges to eliminate campus greenhouse gas emissions. Signatories include Boise State University, Eckerd College, Indiana State University, Temple University, and University of North Texas.

Seems like every school has its own take on what’s earth-friendly, and the efforts are often run by the students. You might find co-eds timing their showers in a “sustainability” dorm like Oberlin’s Student Experiment in Ecological Design house. Or you can do it in the dark with students at Williams College — they turned out lights for the whole month of April as an Earth Day experiment.

No matter what the campus is doing, you can make the college years more eco-friendly on your own. Work in some of these environmentally friendly tips like putting CFLs in your dorm lights and using your printer wisely. The Green Student U site has more ideas, plus you can post your own suggestions.