Photo: Illustration by Gaby D'Alessandro

How green can a pet owner be? It depends who you ask. A few years back a pair of sustainability experts from New Zealand famously equated owning a large dog to driving an SUV. Outraged pet owners were quick to retort: Show us the SUV that gives you unconditional love, lowers your blood pressure, soothes your anxiety, helps you recover from major surgery faster, and gets you marching around the neighborhood three times a day. The truth is, even some of the most hair-shirted among us feel life’s hardly worth living without our cherished dog or cat. So how do we green up that yellow lab or orange tabby?

The Green Diet

The lion’s share of the ecological footprint created by dogs and cats comes from their meaty diets. Determining what makes a greener diet creates a dilemma, though—or at least something of a balancing act. There’s a growing trend among pet food companies to market their products as “free of meat byproducts.” People in some urban areas are opening small-label, local, organic pet food businesses. And some pet experts advocate avoiding commercial pet food altogether by buying human-grade organic meat at the grocery store and making your own pet food at home. Recipes for homemade pet food abound on the Internet.

If you buy commercial pet food, you need to read between the lines, says Marion Nestle, the Paulette Goddard Professor of Nutrition, Food Studies, and Public Health at New York University and coauthor of the book Feed Your Pet Right. She has no problem with organic pet food, which, if you can afford it, is healthier all the way around—for the planet, farmers, wildlife, livestock, and consumers. It’s eschewing meat byproducts that Nestle calls un-green.

Meat byproducts are the parts of slaughtered livestock humans don’t generally consume—organs, intestines, lungs, ligaments, and “mechanically separated meat.” Because these sound disgusting, we think of them as inherently unhealthy. But that’s not necessarily true, Nestle says. “Meat byproducts come from the same animals we eat—they’re just different parts. We don’t eat them for cultural—not nutritional or safety—reasons.” Furthermore, she points out, no matter what commercial pet food makers may say in their marketing, all of them use meat byproducts of some kind. Nestle believes pet food can provide a useful ecological opportunity. “The byproducts of human food consumption cause an enormous waste problem. Feeding them to pets seems like a better use than burning them, putting them in a landfill, or turning them into fertilizer,” she says. “If we didn’t feed byproducts to pets, the dogs and cats in the U.S. alone would need the amount of food it would take to feed 32 million humans, on a calorie basis.”

Clark Williams-Derry, deputy director of programs at Sightline, a Seattle-based think tank, tends to agree with Nestle. “If you’re trying to lighten your pet’s impact, those ‘spare’ livestock parts are basically equivalent to the sawdust generated by the lumber industry,” he says. “The sawdust isn’t without value, but it’s incidental—a low-value byproduct of saw-log production.”

The byproducts versus high-quality-cuts argument holds true when it comes to gourmet cat food made from wild-caught fish and seafood, according to aquaculture and marine policy experts Sena De Silva and Giovanni Turchini. In an article on the website of the Wildlife Society, the scientists describe the pet food industry as a “relatively new and aggressive player in the competition for ocean resources . . . producing and marketing premium brands that use a significant amount of fish that may be suitable for direct human consumption.” Based on De Silva and Turchini’s findings, cat owners should pass on high-end, fish-based cat food.

In fact, there is good reason to avoid canned food altogether. The epoxy-resin lining used in cans leaches the chemical bisphenol A into food—bad for pets and bad for humans. Researchers have found a possible link between exposure to BPA and the rising rate of hyperthyroidism in cats. (High BPA levels in humans have been correlated to an astounding array of maladies, including obesity, heart disease, and the early onset of puberty in girls.)

Conventional pet food that comes in a paper bag with a grease-proofed paper liner also contributes nasty chemicals to the food. That grease-proofing is likely a carcinogenic perfluorochemical, or PFC, and PFCs can and do slough off onto the kibble. Despite plastic’s shortcomings, a plastic bag may be safer for dry pet food.

Putting all this together, what constitutes a green pet diet? Look for organic pet food bagged in plastic, and don’t turn up your nose at meat byproducts.

The Back End

This brings us to our pets’ prodigious output: more than six million tons of it a year in the United States alone. More than just a curbside mess, feces carry potential health threats. Dog poop can contain E. coli, Salmonella, Giardia, roundworm, and other possible pathogens that are trans- missible to humans and wildlife.

Cat poop contains far worse. House cats are a primary reservoir for a protozoan parasite called Toxoplasma gondii, a pathogen associated in humans with miscarriages, fatal food poisoning, encephalitis, and even schizophrenia. Toxo is common in the soil in urban and suburban areas, where house cats use flowerbeds as litter boxes.

In a shocking discovery in the 1990s, the mysterious agent killing sea otters off the California coast turned out to be toxoplasmosis. It’s possible the parasite was carried to the ocean in runoff and in cat poop flushed down toilets. (Although sewage treatment kills many pathogens, it does not necessarily kill Toxo.) Today scientists attribute roughly 16 percent of sea otter deaths to Toxo. This kitty-litter parasite has spread throughout the oceans, and has been found in dolphins, walruses, beluga whales, and even polar bears, with as-yet-unknown health consequences.

Because of Toxo, cat poop should not be flushed down toilets, no matter what the kitty-litter bag tells you. Instead bag poop tightly in plastic and dispose of it in the garbage. As to the litter itself, some kinds are more environmentally friendly than others. The Environmental Working Group recommends avoiding clay-based silica, clumping, and sand kitty litters because these mineral-based products are essentially strip-mined; the group also frowns on cedar shavings and scented litters because the natural aromatic oils and chemical scents can trigger allergies and other health problems. Litters they consider greener include plant-based products made from wheat, corn, ground corncobs, alfalfa pellets, and recycled newspaper pellets.

Dog owners have more options for disposing of poop. First, look online to learn what your local garbage and sewage utilities want you to do. Some prefer that dog poop be tightly bagged in plastic and put in the garbage. In this case, don’t bother buying biodegradable dog poop bags. These are a waste of resources because the low-oxygen conditions inside today’s modern sanitary landfills permit little biodegradation. Instead reuse the ordinary plastic bags that inevitably make their way into your household.

Other utilities recommend flushing dog waste down the toilet—if you’re willing. You can scoop the poop in a plastic bag, empty it into the toilet, tie off the dirty bag, and chuck that in the garbage. Slightly less green but way less gross are new, flushable dog poop bags made for this purpose. Buyer beware, though. These work best with the output of a small dog; because the bags keep the waste in a clump, they can easily clog a toilet.

Some dog owners have a third, and uber-green, poop-disposal option within their reach, though it’s not for the faint of heart. If you have a smallish dog, sandy soil, and a yard, you can compost dog poop at home.

Sharon Slack, of Vancouver, British Columbia, has composted her dogs’ poop for years. Her system is simple: She cut the bottom out of an old garbage can and punched a few holes in the sides, then buried it up to just below the rim in an out-of-the-way part of her garden. She uses a small shovel to dump poop into the bin and occasionally sprinkles it with water and an over-the-counter enzyme product used in septic systems. When the compost is finished, she spreads it under her shrubs and starts another batch.

Stopping the Predators

Pets’ impact on wildlife is a serious and seriously contentious environmental issue. A wildlife biologist who estimated and published the number of wild birds killed annually by rural cats in Wisconsin (39 million) reportedly received death threats from cat fanatics.

In 2011 the Journal of Ornithology published the results of a study on the fate of fledgling Gray Catbirds equipped with tiny transmitters around suburban Washington, D.C. Eighty percent of the babies were killed, roughly half of them by house cats.

Naive babies cheep loudly and flap conspicuously to get their parents’ attention, making them particularly vulnerable to feline hunters, which have all day to observe, stalk, and kill in the lovely suburban shrubbery that attracts nesting songbirds in the first place. (Some research shows that putting bells on cats does not save birds.)

Though it goes against the grain, cat owners must start keeping their cats indoors. Indoor cats live healthier and longer lives than outdoor cats. They are less likely to spread—or catch—Toxo. And the cats can be perfectly content. The Humane Society and the American Bird Conservancy offer online tips for fighting feline boredom. Even if you keep your cat indoors only in spring and summer, you can make a difference.

Dogs don’t get off the hook on this one either. A 2007 study in Australia documented an astounding 35 percent decrease in bird species diversity and a 41 percent decrease in bird abundance in places where dogs were walked.

Birds that nest on beaches are particularly vulnerable to dogs, says Julie Wraithmell, director of wildlife conservation for Audubon Florida. One of Wraithmell’s main concerns is the Snowy Plover, threatened in Florida. “People don’t realize that when dogs run on the beach and flush Snowy Plover adults off nests, the hot sun can kill the exposed eggs and chicks in as little as two minutes. There are fewer than 500 adult Snowy Plovers left in the state.”

Dogs are beloved members of our families, and we want to take them out with us, says Wraithmell, a dog owner herself. But there is precious little beach habitat left for shore-nesting birds. “Ironically, many dog owners frequent more remote stretches of beach so as not to bother other people with their dogs, seldom realizing these isolated spots are wildlife’s last refuge.” Take your dog only to beaches with designated dog areas, Wraithmell urges.

If you’re in the market for a new pet, start green from the get-go: Adopt your cat or dog from a shelter. Spay or neuter your pet. Keep cats indoors and dogs on leashes except for within designated off-leash areas. And if you’re getting a new dog, choose a small one. Think: dog equals motor scooter.

This article ran in the July-August 2014 issue.