Despite this deep lineup of energy conservation measures, many methods for greening up the national pastime remain. The NRDC's Hershkowitz emphasizes that all teams need to start using recycled paper, for instance, for everything from game programs to toilet paper.

Transportation looms large, as well. "At the end of the day, the biggest contribution to baseball's carbon footprint is people driving to the game," says Michel Gelobter, the founder and CEO of Cooler, an Oakland, Calif.–based software firm that tracks carbon footprints and reduction methods.

He believes future stadium site selections should encourage fans to use mass transit system access instead of clearing acres of land for parking lots. A good example of this, Gelobter says: The Number "7" subway that shuttles fans between Midtown Manhattan and Queens to see the New York Mets play, as well as the public transport available in Atlanta to carry people to the Braves's stadium there.

With a bigger rollout of renewable energy sources such as solar and wind (Cleveland is looking into adding turbines), Gelobter envisions a time when stadiums could perhaps generate more power than they consume. "The ability for stadiums to become smarter with their electricity use and even make power is much better than their being an energy sink," he says. Hershkowitz says his organization estimates that about 70 percent of energy at MLB parks comes from fossil fuels, and less than 1 percent from renewables like solar and wind.

Hershkowitz and others hope that baseball and other professional sports' green moves will serve as a model for others. "The biggest payoff from this green effort may a cultural shift," he says.

Brendan Owens, the vice president of LEED technical development for the USGBC, agrees. "If team organizations can capitalize on the educational opportunity they have as a result of a million or two million people coming through their gates every year, that can have a significant ripple effect throughout the community," he says

Gelobter believes that the advent of greater greening brought about through sport bodes well in the face of increasingly dire climate change assessments. "I think it's good to align artistic and athletic expression," he says, "with the long-term health of the planet."