What's worse ... having a dog or driving an SUV? The answer might surprise you.

Robert and Brenda Vale, two architects who specialize in sustainable living recently took a look at the comparative eco-impact of pet ownership and other lifestyle choices in their new book, "Time to Eat the Dog: The Real Guide to Sustainable Living." In the book, the authors compare the environmental costs associated with feeding and caring for pets with the environmental costs of say, driving an SUV. The pets did not fare well.

To analyze and compare a pet's ecological pawprint, the Vales examined the ingredients of common brands of pet food. For example, they calculated that a medium-sized dog would eat about 90 grams of meat and 156 grams of cereals daily if he were given the recommended 300-gram portion of dried dog food. Taking into account the amount of land and resources required to produce these meats and cereals, the Vales estimate that a medium-sized dog would have an-eco footprint of 0.84 hectares. For a big dog such as a German shepherd, the figure is 1.1 hectares.

Meanwhile, to examine the eco-impact of driving an SUV (the Vales used a 4.6-liter Toyota Land Cruiser for their comparison), the authors estimate that even driven a modest 10,000 kilometers (or about 6,200 miles) a year, the SUV would need 55.1 gigajoules to fuel and build it. One hectare of land can produce about 135 gigajoules of energy per year, so the Land Cruiser's eco-footprint is about 0.41 hectares — less than half that of a medium-sized dog.

OK, so dogs are out? (Please don't tell my lab-mastiff mix that he's got the eco-pawprint of a Hummer!) How did other animals do? Using similar calculations for a variety of pets and their foods, the Vales found that cats have an eco-footprint of about 0.15 hectares (slightly less than a Volkswagen Golf. Considering the U.S. is home to some 76 million cats and 61 million dogs, that's quite a big environmental impact.

Slightly less ominous were the eco-impacts of smaller animals like hamsters (0.014 hectares,) canaries (0.007 hectares,) and goldfish (0.00034 hectares.)

And it's not just the food. As well as guzzling resources, cats and dogs can devastate wildlife populations, spread disease and add to pollution. 

So what's an eco-minded pet-lover to do? For starters, talk to your veterinarian about reducing the amount of meat in your pet's diet. Your vet should be able to point you in the right direction for recipes and pet food brands that use less meat but still deliver all of the nutrients your pet needs.  Also, consider adopting a pet rather than purchasing from a breeder to minimize overbreeding and lighten the burden on animal shelters.  

The opinions expressed by MNN Bloggers and those providing comments are theirs alone, and do not reflect the opinions of MNN.com. While we have reviewed their content to make sure it complies with our Terms and Conditions, MNN is not responsible for the accuracy of any of their information.