St. Patrick's Day is as green as holidays get. (OK, maybe Earth Day beats it on a technicality, but clearly the drinks are better on March 17.)

Traditions range from green beer in brewpubs to the dyeing of the Chicago River emerald green for the day. But whether it's the anticipation of spring or just an excuse to take the day off and party, St. Patrick's Day parades bring crowds to the streets from New York City to Serbia, Montserrat to Croatia.

One scientist wants parade organizers to think about materials, energy and waste with the same excitement they show hoisting their beer mugs.

"If you go to Home Depot and buy virgin lumber for your float, and then tear it apart and put it in a Dumpster, that's bad," says Michael Patrick McCann, biology professor at Saint Joseph's University in Philadelphia.

"On the other hand, if you build it, dismantle it and then find some other use for it next year, that's a big plus," adds McCann, a half-Irish, half-German/Czech/Italian microbiologist who also heads the university's sustainability committee.

New Yorkers have had fairly eco-friendly parades for centuries. The first parade in the city to honor the patron saint of Ireland was organized in 1762. Those early marchers represented church parishes, trade and military organizations, and were greeted by the archbishop at the site of the old St. Patrick's Cathedral.

It turns out traditions haven't changed much since then. The two-mile New York City parade, now along Fifth Avenue, is still Earth-friendly. Just like in 1762, there are no cars, no floats, no buses, no trucks. There are just marchers, about 150,000 strong, including, according to the parade's website, "any politician running for office within a 50-mile radius."

But whether it's a parade in New York or New Zealand, the spectators, especially those fortified with adult beverages, can leave an ugly footprint. Public transit and proper beverage containers can help reduce that, McCann says.

"I know some people might become inebriated during the celebration," he says. "Anytime you plan to go out and drink, you shouldn't drive to begin with; you should use mass transit to get to and from the party."

And he advises parade-goers to bring drinking water in reusable plastic bottles. McCann is no fan of clamshell take-out containers or juice boxes.

"Most are made with materials that can't be reused or recycled. Juice boxes are almost impossible to recycle, because they contain a mixture of paper, aluminum foil and plastic," he says.

One of the biggest and most boisterous St. Patrick's Day festivities in the United States is in Savannah, Ga. This year the city's parade entry is celebrating a vibrant new sustainability effort called "Thrive," designed to reduce the city's carbon footprint by 15 percent.

"We started gaining momentum over the past eight months," says Thrive coordinator Rachel Smithson.

To celebrate that success, there's no fume-spewing flatbed truck toting a city float. Instead, city employees will be walking, biking and picking up trash along the parade route. They'll be joined by mascots Rennie the Recycler, Les Waters (promoting water conservation) and Naz T. Butt, a character from nearby Tybee Island who battles cigarette litter. The city's sanitation department will also provide recycling bins throughout the city during the parade.

St. Patrick's Day has morphed over the years from a religious holiday to a secular one, a day when "everyone is Irish."

McCann says the large Catholic and Christian student body at his university make a connection between religion and protecting the planet.

"The Catholic Church has stated [that] stewardship of the planet is a requirement. God didn't say, 'Do with it what you will.' We've got to take good care of what we've got," he says.

And if the recycling thing doesn't quite register with his students?

"I'm planning some landfill field trips, to let them see what big, ugly, holes in the ground they are," McCann says.