Dec. 23, 2009 -- Taking the dog for a walk to the store would seem like a more environmentally-friendly option than piling into the SUV.
Not so, say two New Zealand scientists whose new book claims pets have a carbon footprint that is about twice the size of the gas guzzling vehicles that have long been a bane of environmentalism.
In "Time to Eat the Dog, the Real Guide to Sustainable Living," Robert and Brenda Vale charge that a medium-size dog has a footprint of 2.1 acres compared with slightly more than one acre for a standard sport utility vehicle.
The New Scientist Web site relayed other carbon footprint comparisons from the Vales' book. Cats are roughly equal to small Volkswagens while two hamsters have the same footprint as a plasma television. Goldfish are comparable to a pair of cell phones.
"There is no question but that pets do exert a claim on resources," Lester Brown, president of the Earth Policy Institute in Washington, D.C., told ABCNews.com.
"Dogs and cats are carnivores so they consume meat, which means they live rather high on the food chains," he said. "Much higher than the typical person in the sense that most of us -- even those who are omnivorous -- eat a lot of fruits and vegetables and cereals and other things."
Meat requires a high amount of land and energy to produce as opposed to cereals, raising the carbon foot print of carnivors.
The Vales rationalize, according to New Scientist, that dogs and cats take up much of the planet's natural resources because of their diets. They estimate that a medium-sized dog eats about 361.5 pounds of meat each year and that it takes about 1.67 miles to cultivate just 2.2 pounds of chicken. The numbers for beef are higher.
Wayne Pacelle, president and CEO of the Humane Society of the United States, said it was irresponsible to lay blame on domesticated animals without looking at human consumption.
"I think the first instinct should be to look at our own diet and not push off the global warming causes to domesticated animals," Pacelle told ABCNews.com. "If this is their primary thesis, it's an example of over magnified concern and we need to look to our own behaviors, not just energy consumption and transportation, but also our diet."
Do Animals' Benefits Outweight Their Drain on Resources?
Pacelle noted that in the United States alone, the agriculture industry is a major player in greenhouse gas emissions. "It is our own consumption of these products that is the primary problem," he said.
On top of that, he added, dogs and cats "aren't driving to work."
According to the American Pet Products Manufacturers Association 2009-2010 National Pet Owners Survey, 62 percent of Americans, or more than 71 percent of U.S. homes, own at least one pet.
More than 45 percent of households own at least one dog, while more than 38 percent own at least one cat. According to the previous study for 2007-2008, most dog owners have two dogs while 12 percent of dog owners have three or more.
The APPA also estimated that the pet industry will total $45.4 billion in 2009, compared with $43.2 billion last year and $23 billion in 1998.
For all that money spent, pets do come with benefits.
When pets and their owners are together, Pacelle said, "We release and the pets release oxytocin and it lowers our blood pressure and relieves stress and anxiety.
"As a general measure they are an antidote to loneliness and give us great friendship and companionship," he said.
Scientist: Pets Make Environmental Demands Just Like Humans
Scientists like Brown, however, aren't advocating that domesticated animals go the way of the eight-track tape.
"Any claims on the Earth's resources, whether it's having pets or having children, we need to think about. It doesn't necessarily mean getting rid of your pet now. But when the pet dies, as they eventually do, you might want to think about whether you replace it or not," he said.
"I don't think there's any way of saying how many pets somebody should have or a country should have," Brown added. "But it is useful to think about the environmental demands that pets make in the same way that people do."
Pets are an "irreplaceable feature of our lives and our culture," Pacelle said. "And there's no stepping back."