Bad news for environmentally conscious pet owners: cats’ and dogs’ eating habits are responsible for dumping as many as 64 million tons of greenhouse gases into the atmosphere every year — roughly the equivalent of driving over 13 million cars. That’s due to all the meat our furry friends gobble down, according to new research.

There are more than 163 million dogs and cats in the US, and they just love to eat. In fact, cats and dogs in the US consume about 19 percent as many calories as people do in the US, or about as much as 62 million Americans, according to a new study published in Plos One. Because much of that food is meat, and meat production is known to heavily contribute to climate change, our pets leave a pretty stark carbon footprint on our environment.

they just love to eat

Raising livestock for meat takes up land, water, and energy, which pumps lots of heat-trapping greenhouse gases into the environment. It takes 24 kilograms of carbon dioxide to make one kilo of pork, and 1,000 kilos of CO2 to make just one kilo of beef, according to a study by the Proceedings of the National Academy of Sciences. When we talk about climate change, we often think about how much meat people eat. But Gregory Okin, a geographer at UCLA, wanted to focus on pets.

By calculating the number of dogs and cats in the US, their average weights, and ingredients in pet foods, Okin tallied the carbon footprint of our animal friends. His findings: American cats and dogs consume about 19 percent as many calories as people do in the US; and because they’re mainly meat-eaters, they consume about 30 percent of the animal-derived calories that people consume. They also produce 30 percent as much poop as Americans do. (If all those feces were disposed as garbage, it’d be equivalent to the total trash produced by over 6 million Americans, or approximately the population of Massachusetts, the study says.) All in all, American cats and dogs are responsible for producing about 64 million tons of methane and nitrous oxide, two powerful greenhouse gases that contribute to climate change, according to Okin’s calculations.

Maybe you can just opt for a hamster, instead

The findings are meaningful because pet ownership is skyrocketing in Asia, and that means dogs’ and cats’ environmental footprint is just going to increase. You could make the argument that only leftover meat goes into pet food, so if animals didn't eat it, it would be wasted. But in the US, pet owners are also increasingly feeding their animal friends gourmet food that has higher-quality meat (what’s referred to as “human-grade” on pet food packaging). That means that pets aren’t just eating leftover meat, like animal organs, that people find too revolting to swallow. So their meat consumption should be considered an add-on to our own.

The study doesn’t go too deeply into what pet owners can do about this: after all, cats — even more than dogs — need their protein. But pet owners could be more careful about pet food ingredients, like choosing plant-based proteins when they can, or just reducing the amount of treats pets get. (Obesity is a major problem among domestic animals, the study points out.) Or maybe you can just opt for a hamster, instead.

“This analysis does not mean to imply that dog and cat ownership should be curtailed for environmental reasons,” Okin writes in his study, “but neither should we view it as an unalloyed good.”