When Mary Ann Windsor maneuvers her banana-yellow Hummer H2 around town, it often becomes an act of defiance.

Drivers and pedestrians flip her off. Kids tell her she's killing the planet. Grown-ups leave "nastygrams" on her windshield.

"I can't understand how people here are so rude and so nasty about our (sport-utility vehicle)," she said.

Yet the hostility only emboldens her. Her Hummer, perhaps the world's most reviled gas guzzler, gets 10 miles or less per gallon in the city. Perched high in her cab, Windsor feels safe driving in the snow with the children in her day-care business and armored against drunken drivers. Besides, she said, it's no one's business what she drives. "I don't feel guilty at all," she said.

Hoping to one-up her critics, she and her husband, Bob Windsor, bought carbon offsets. A $49 donation to the nonprofit Carbon Fund provided enough offsets to match the nearly nine metric tons a year of carbon dioxide her Hummer chugs out. Her badge of righteousness, a Carbon Fund decal, is affixed to her rear window. "It's just, in crude terms, to shut people up," Bob said.

The sticker provided a ready comeback a few weeks ago when a group of kids outside the Santa Fe School for the Arts ridiculed her ride. "I have carbon credits so my car is actually cleaner than a Prius," Mary Ann told them. "You can pay for my gas or you can pay for my insurance; otherwise, you and your hippie parents can just be quiet."

But is it that simple? Does buying carbon offsets, which are also called credits or green tags, absolve us of our greenhouse-gas producing ways? Supporters say carbon offsets pump money into renewable-energy projects which, ideally, could help wipe out the need for coal-fired power plants. Cynics see offsets as a piecemeal approach to a larger mess that needs greater involvement by governments and corporations.

Some view offsets as a scheme that targets enviros seeking to quell their guilt. A satirical Web site, www.cheatneutral.com, solicits people who cheat on their partners to pay monogamous people to remain faithful. "This neutralizes the pain and unhappy emotion and leaves you with a clear conscience," it quips.

Dozens of credit-selling outfits — both nonprofit and private — have popped up in the past few years. People pay money to offset their commutes, plane trips or the fossil fuels that power their homes or small businesses, and the sellers invest in wind and solar projects, energy-efficiency technology and reforestation. A credit often equals 1 metric ton of carbon dioxide emissions, and some sell for as little as $5.

New York City environmentalist and author Colin Beavan said offsets have their place, and he buys them for his airplane flights and train trips, but they obviously can't retrieve the carbon we routinely put into the atmosphere from driving cars or flipping on the lights.

"Let's say that I was to drop a piece of my garbage and it ends up in the ocean," he said. "Then I go to the beach and pick up a piece of garbage that I see. That's a good thing, but my piece of garbage is still in the ocean."

Beavan, better known as No Impact Man, recently completed a yearlong experiment in which he and his wife and their young daughter stopped using the elevator in their Greenwich Village apartment, riding the subway and using their appliances. They did their laundry in the bathtub, composted their garbage, avoided packaged products, bought only locally grown food and got by at night with candles as he blogged on his solar-powered computer.

"We have to be really careful that the idea of carbon offsets isn't some kind of salve for our conscience," Beavan said.

Brad Mewhort recently sought to offset his entire carbon output, going back 33 years to his birth. The Seattle resident tried to account for the heat and lighting for the house he grew up in, the vehicle his parents used to cart him around, the cars he's driven and the vacations he's taken, including a recent trip to Antarctica. He has so far donated $3,600 to Carbon Fund, which is based in Maryland.

"I don't think it's a perfect solution," he said. "But it's hard to live in this society without a carbon footprint, so I think it's a good compromise."

He got to thinking about his life's carbon production while in Antarctica, an experience he said was "a hundred times more magnificent than I'd ever imagined." But along with penguins and seals, he saw huge chunks of glacial ice falling off the continent. "That always happens, but it's happening at a much faster rate," he said. "Those are glaciers that take thousand and thousands of years to form, and they're falling off — they're not being replaced."

The software company manager sold his Honda Civic last fall, gets around by walking and sticks to a mostly vegan diet. "I have the occasional cheese," he said.

The Windsors, meanwhile, remain unconvinced about whether they're helping the planet. They installed compact fluorescent light bulbs throughout their Rancho Viejo home and try to recycle. But they consider Al Gore a hypocrite for having flown in private jets and are generally leery of claims that fossil fuels are warming the earth.

"I believe carbon credits are probably a scam, a method for people with money to behave the way they want to behave," Bob Windsor said. After a pause, he added: "I believe in global warming. I'm just still not sure how much man is the cause."

Mary Ann Windosr, however, didn't hedge: "I think it's something the Democrats made up."

Sometimes people's motives for helping the environment are irrelevant, said Beavan, who plans to release a book about his carbon-free year next January.

"The Hummer owner is not doing it because she wants to help the climate, but that's OK," he said. "I'll take her money."

Contact Doug Mattson at 986-3087 or dmattson@sfnewmexican.com.

www.b-e-f.org
www.carbonfund.org
www.cheatneutral.com
www.greenenergynm.org
www.hummer.com
www.noimpactman.typepad.com