By ALEX WILLIAMS

Despite the expense and the occasional back strain, Mary Burnham, a public relations consultant in San Francisco, felt good about the decision she made a few years ago to buy milk - organic, of course - only in heavy, reusable glass bottles. For the sake of the environment, she dutifully lugged them back and forth from the grocery store every week. Cutting out disposable paper cartons, she reasoned, meant saving trees and reducing waste.
Or not. A friend, also a committed environmentalist, recently started questioning her good deed. “His argument was that paper cartons are compostable and lightweight and use less energy and water than the heavy bottles, which must be transported back to a plant to be cleaned and reused,” she said. “I have no idea which is better, or how to find out.”
Ms. Burnham, 35, recycles religiously, orders weekly from a community-supported farm, buys eco-friendly cleaning products and carries groceries in a canvas bag.
But she admits to information overload on the environment - from friends, advice columns, news media, even government-issued reports. Much of the advice is conflicting.
“To say that you are confused and a little fed up with the often contradictory messages out there on how to live lightly on the earth is definitely not cool,” she said in an email message. “But, heck, I’ll come out and say it. I’m a little overwhelmed.”
She is, in other words, a victim of “green noise” - static caused by urgent, sometimes vexing or even contradictory information played at too high a volume for too long.
Two years after Al Gore’s “An Inconvenient Truth” helped unleash a new tide of environmental activism, green noise pulses through the collective consciousness from all directions. The news media issues dire reports about disappearing polar bears; Web sites feature Brad Pitt arriving at a movie premiere in his hydrogen-powered BMW; bookstore shelves are piled high with titles like “50 Simple Things You Can Do to Save the Earth”; shops carry hempenriched shampoo and 100 percent organic cotton tampons.
Some environmentalists fear that the public might begin to ignore their message before any meaningful change can be accomplished. For them, it’s a time to reassess their campaigns before it’s too late.
“We worry about it,” said Carl Pope, the executive director of the Sierra Club. “We all understand that today’s media environment is an extremely crowded one, and message overload is the order of the day.”
Erik Michaels-Ober, a 24-year-old software engineer in San Francisco, said: “I would be a much more productive member of society if I didn’t have to worry about, ‘Should I wash dishes by hand or run the dishwasher-’ There are all sorts of conflicting stories about that.”
In a way, the heightened public awareness about global warming shows that the early public campaigns were successful, said Chip Giller, the founder of grist.org, an environmental news and information Web site.
Along with that success came a torrent of green products from marketers. And it is these eco-pitchmen, trumpeting claims that are not always substantiated, whom Mr. Pope blames for generating much of the green noise.
But others in the environmental movement say activists and nonprofits must shoulder their share of responsibility, too, for bombarding people with messages. “The groups that are trying to get them to change overwhelm them with information,” said Diane Tompkins, a founder of the Curious Company, a market research firm based in San Francisco.
“The fact is, people are not motivated by more facts,” she said. “That can just reinforce their feeling of helplessness.”