In fact, the annual greenhouse-gas emissions from the production of junk mail are equal to those of 3.5 million cars. (That figure doesn’t include emissions from transporting and disposing of the stuff.) Beyond that, each year junk mail production in the U.S. consumes more than 96.7 billion gallons of water and more than 100 million trees, ForestEthics estimates. Most of those, says Chester Vance, come from carbon-dioxide-sequestering, biologically diverse old-growth forests, rather than from sustainably managed tree farms. And according to the Environmental Protection Agency, only about a third of all junk mail is recycled. “All that for a response rate of less than 3 percent,” Chester Vance notes, referring to the fact that fewer than 3 percent of people — often even fewer — respond to the solicitations.

Junk mail has nonenvironmental problems too. It exposes you to identity theft and is just a drag to sort through. If you spend five minutes a day dealing with junk mail — shredding credit card offers, for instance — you blow a full 30 hours a year. Time you could use to write the great American novel, hang out with your kids, or gaze up at the stars.

Usually your name and address end up on junk mail lists because you’ve purchased something with a credit card, subscribed to a magazine, or listed your name and address on the application for a store’s discount card. Merchants sell your information to others. You may have tried stopping your junk mail in the past, perhaps by contacting the Direct Marketing Association, the largest industry trade group, to little or no avail.

But fighting the junk mail hydra requires a multipronged approach, one that environmental groups and Internet-based service providers are taking up in equal measures. Now, several paid and some free services can effectively stop between 80 and 95 percent of all that mailbox clutter.

One such service is the Palo Alto, Calif.-based GreenDimes.com. For a $15 one-time fee, GreenDimes will “contact a dozen or so direct-mail groups on your behalf,” says general manager Dan Estabrook. GreenDimes instructs these groups, which compile and sell names to countless companies and banks, to remove your name and address — including past residents and the omnipresent “current resident” — from their databases. GreenDimes also monitors the DMA’s distribution list on a monthly basis to make sure your name is not included. “On the catalog side, we communicate directly with thousands of catalog companies, indicating that you’ve authorized us to remove your name,” Estabrook says.

GreenDimes’ coverage should last for three to five years, he estimates. If you move, you need to re-up. Like other services, GreenDimes allows consumers to choose, for the life of the membership, which catalogs they’d like to receive and which they’d like to stop. And with each new membership, the group plants 10 trees through tree-planting groups American Forests, Sustainable Harvest International, and Trees for the Future.

Ferndale, Mich.-based nonprofit 41pounds.org — its name is based on the average amount of junk mail a person receives each year — offers a similar service. For $41, it guarantees to stop junk mail for five years. It erases your name from direct mailers like Valpak, ShopWise, Reader’s Digest, Publishers Clearinghouse and Bed Bath & Beyond. It also donates $15 of your fee to nonprofits such as Stopglobalwarming.org.

Stopthejunkmail.com will put the brakes on junk mail to small businesses as well as consumers, for $20 a year.

None of these junk-mail-stopping services has been rated by consumer organizations such as Consumer Reports. But ever since signing up for GreenDimes this summer, I can happily report that my junk mail has stopped; the only pieces I now receive are from the environmental groups to which I belong.

If you don’t want to pay anything to stop junk mail, check out Catalog Choice, organized jointly by the Natural Resources Defense Council, the National Wildlife Federation, and the Berkeley, Calif.-based Ecology Center. The Web site allows individuals and businesses to remove their names from the mailing lists of catalogs they don’t want. Simply register, find the names of the catalogs you no longer wish to receive, enter the requested information into the Web form and click “Decline.” Catalog Choice will then contact merchants on your behalf.

Why focus on catalogs? Although they constitute only about 15 percent of the direct-mail pieces sent out in 2006 — that’s about 15.5 billion catalogs — “they have a disproportionate effect because of their weight,” explains the NRDC’s Kate Sinding. Sinding believes consumers aren’t the only ones who will benefit from the service. “We think this will help merchants, who can mail to people who want to get their catalogs and not waste money mailing to people who don’t,” she says.

Of course, the junk mail industry is hip to the fact that most people loathe much of what they produce. So the Direct Marketing Association is getting in on the act, sort of. Its new Commitment to Consumer Choice requires its 3,600-plus member companies to “notify consumers of the opportunity to modify or eliminate future mail solicitations.” As of October 2008, you should see a line on every piece of junk mail that explains how to get your name removed from the companies’ mailing list. If not, says DMA senior vice president for corporate responsibility Patricia Kachura, you should rat them out to the DMA. “Failure to comply means they can be brought to the DMA board of directors and could be expelled from the association,” Kachura says.

The DMA has also made nonbinding environmental recommendations, such as increasing recycled-paper content. And, for $1, the group offers its own consumer Mail Preference Service. The service claims to remove individuals from DMA-member lists; it doesn’t remove them from the lists of nonmember companies or from credit card or other financial solicitation lists, which are handled by other concerns. You can opt out of financial solicitations for free, though, by visiting OptOutPrescreen.com, a site jointly run by the four largest credit information agencies.

Finally, in dealing with junk mail, you might want to participate in new efforts by ForestEthics, the Center for a New American Dream and other groups to launch state “Do Not Mail” registries. The registries would prohibit direct marketers from sending unsolicited mail to those who sign up, much in the way the federal “Do Not Call” registry prohibits phone solicitations. “State ‘Do Not Call’ registries led to the creation of the federal ‘Do Not Call’ registry,” says ForestEthics’ Chester Vance, explaining why the groups are focusing their efforts on state legislation first.

The environmental benefits of such a registry could be pretty wide-ranging. And then, hey, think of all the time it could free up to deal with spam.

Earlier that morning, as dignitaries entered the building, PETA made an effort to drive its message home. The group draped its banner across a champagne-colored Hummer and drove it around the State Department. By noon, the Hummer was parked across the street. “The plan didn’t work so well because of security and the way the roads are set up,” confessed Matt Prescott, PETA’s manager of factory farm campaigns.

Undaunted, PETA protesters, in October, drove a truck-mounted billboard around venues in Austin, Texas, and Denver, where Al Gore lectured about climate change. It featured a caricature of the Nobel laureate, potbellied and brandishing a partially eaten poultry drumstick. “Too Chicken to Become Vegetarian?” the billboard taunted Gore, and concluded, again: “Meat Is the #1 Cause of Global Warming.”

Not quite. As Phil Gutis, the Natural Resources Defense Council‘s communications director and an erstwhile PETA member, says, “I wouldn’t look to PETA for science.” The No. 1 cause of global warming is burning fossil fuels for electric power. Still, the group raises an important point. A November 2006 United Nations Food and Agriculture Organization report found that livestock accounts for 18 percent of global warming emissions worldwide, more than the entire transportation sector.

Here in the U.S., livestock’s impact is not quite so extreme: Six percent of our greenhouse gases come from livestock production, compared with 19 percent from cars, light trucks and airplanes. Still, for conscious eaters, those statistics are worth fleshing out.

According to the FAO, livestock production is a top cause of the world’s many environmental problems: deforestation, acid rain, dead zones in the ocean, land degradation, water pollution, species extinction and, most threatening of all, global warming. “We looked at every step of the commodity chain, from feed production to consumption,” says Henning Steinfeld, chief of the FAO’s livestock policy branch.

To begin with, Steinfeld says, “a lot of climate change damage is associated with clearing forest land, either for pastures or for feed crops.” Trees cut down to make room for cattle or soybeans no longer sequester carbon. Those trees are burned or decompose, creating carbon dioxide, the most common greenhouse gas.

Likewise, soil trampled underfoot or exposed to chemical fertilizers and pesticides retains significantly less carbon than forest soil or soil used to produce organic crops. “This is a particularly acute problem in Latin America,” Steinfeld says. Over 70 percent of the Amazon’s deforested land is used for pasture, and a substantial part of the remaining land is used for feed crops. Much of the world’s arable land is devoted to animal feed. In the U.S., 60 percent of the agricultural output of the Missouri-Mississippi basin is used to feed livestock.

Just as significant as those impacts are the potent methane and nitrous oxide emissions generated by livestock production. Livestock emit about a third of human-caused methane production and two-thirds of human-caused nitrous oxide. Cattle, bison, sheep and goats, “because of the specific features of their digestion, release methane from their mouths,” Steinfeld says. In other words, they burp out a lot of methane. That gas traps 23 times more heat per ton than carbon dioxide.

Steinfeld notes that “methane is also released from manure.” That’s particularly true when it’s stored in anaerobic conditions, such as the so-called waste lagoons common in U.S. industrial pork and dairy production, or in manure piles connected to American cattle feedlots. Feedlots are relatively unknown in other parts of the world.

In the U.S., there’s currently much more manure than land to spread it on. Consequently, the slurry is often sprayed on fields at concentrations that exceed by 200 times the underlying soil’s ability to incorporate the nitrogen the manure contains. The result? Nitrous oxide, a product of the manure’s decomposition. As a global warming gas, the compound has a heat-trapping potential 296 times that of carbon dioxide.

The Humane Society of the United States, good cop to PETA’s bad, has mounted its own effort to link livestock to global warming. Along with PETA, it advocates eliminating animal products from our diets, implying that all of these products — meat, dairy and eggs — are equally destructive. But that’s just not the case. “If you want to look at this globally,” says Steinfeld, “beef is absolutely the worst.”

Is grass-fed beef any better than the feedlot kind? Steinfeld says feedlot cows and grazed cattle create about the same amounts of greenhouse gases. Grazing, he says, “is not necessarily an environmentally benign form of production.” Even when deforestation and overgrazing are accounted for, producing beef still requires an enormous amount of land. And, individually, cows fed on forage release more methane that the grain-fed cows of mass feedlots.

Cornell University professor of ecology and agricultural sciences David Pimental disagrees. “Feedlot beef requires twice as much fossil fuel energy to produce as grass-fed beef,” Pimentel says. According to his estimates, producing 1 pound of feedlot beef results in the production of 8 pounds of carbon dioxide. That’s the equivalent of a third of a gallon of gasoline. Despite more burping by cows fed on forage, Pimentel says, their overall emissions remain lower.

Pork and dairy production occupies a middle ground, greenhouse-gas-wise, Pimentel says. Both dairy cows and hogs need a lot of feed, most of which is produced using nonorganic methods. But milk cows require less grain to make their product than do their cattle cousins. And pigs don’t belch methane, although the waste lagoons associated with industrial pork production do. The same goes for waste from large dairy operations.

Welcome, then, the savior of environmentally concerned carnivores everywhere: the chicken. Unlike cattle, chickens don’t burp methane. They also have an amazing ability to turn a relatively small amount of grain into a large amount of protein. A chicken requires 2 pounds of grain to produce a pound of meat, compared with about 6 pounds of grain for a feedlot cow and 3 pounds for a pig. Poultry waste produces only about one-tenth of the methane of hog and cattle manure.

That’s not to say chicken production is pure. The waste often contains the cancer-causing element arsenic, which is added to most U.S. chicken feed to promote growth. Plus, chicken poop frequently has mercury in it, possibly from fish meal used as feed, or from vaccines. And let’s be clear: The life of an industrially raised chicken is not a happy one. The growing birds are warehoused in spaces so small they can’t flap their wings, turn around or preen. Breeding for maximum meat production has resulted in animals whose bodies have difficulty supporting their own weight, meaning chickens live much of their lives in pain.

Still, chickens are such efficient producers of protein that a study in the science journal Earth Interactions finds that Americans who eat poultry, dairy and eggs, but not red meat, are responsible for fewer greenhouse gases than those who consume a vegetarian diet that includes dairy and eggs. “Astonishingly enough,” says study coauthor Gidon Eshel, a Bard College geophysicist, “the poultry diet is actually better than lacto-ovo vegetarian.” In other words, a roast chicken dinner is better for the planet than a cheese pizza. “If you need to eat dead animals, poultry is the way to go,” says Eshel, a vegan.

Eshel suggests that those eating with the climate in mind also steer clear of “large, predatory fish,” such as tuna, swordfish and shark. To catch them, he notes, “you have to schlep halfway across the ocean, and then you come back with less than a paltry amount of edible meat. It’s a big energy investment.” Salmon farming is also notoriously energy inefficient, Eshel says. He advises fish lovers to turn to sardines, anchovies and herring, or any non-overfished coastal species.

Eshel notes that the difference between a vegan diet and one that includes cheeseburgers is less than 2 tons of greenhouse gases a year. That’s about the equivalent of switching from a Camry to a Prius. The average American is responsible for about 26 tons annually, so if the entire U.S. population went vegan, we’d reduce our greenhouse gas emissions by only 6 percent.

How can you combat global warming with your fork? Simply by consuming less beef, pork and dairy. Choose beef products produced in the U.S. rather than in Latin America. And generally speaking, pick grass-fed meats and those produced on small, local farms rather than in industrial operations. Beef eaters might also want to keep an eye out for the USDA’s forthcoming “grass-fed” label, which has received high marks from a number of environmentalists and small-farm advocates.

Becoming a vegan is your best choice. But if despite all rational arguments, you find yourself jonesing for some flesh, look to PETA’s mobile billboard for inspiration, and have yourself a drumstick.