Many probably have never thought about their pets’ role in global warming. According to a study published on Wednesday, animal agriculture for dogs and cats contributes to about a quarter of greenhouse gas emissions in the US.

In a paper published in the journal PLOS One, Gregory Okin, a geography professor at University of California, Los Angeles (UCLA), says that cats and dogs are responsible for 25 to 30 percent of environmental influence due to meat consumption.

Okin calculated that dogs and cats’ meat eating habits generate an equivalent of about 64 million tons of carbon dioxide per year, which equals to the impact caused by a year's worth of driving from 13.6 million cars.

"I like dogs and cats, and I'm definitely not recommending that people get rid of their pets or put them on a vegetarian diet, which would be unhealthy," Okin said. "But I do think we should consider all the impacts that pets have so we can have an honest conversation about them. Pets have many benefits, but also a huge environmental impact."

Meat production is a huge part of animal agriculture. It is therefore one of the biggest global warming factors. Greenhouse gases are generated during meat manufacture, and again during the transportation of the final products.

"As pet ownership increases in some developing countries, especially China, and trends continue in pet food toward higher content and quality of meat, globally, pet ownership will compound the environmental impacts of human dietary choices," Okin writes in the study. "Reducing the rate of dog and cat ownership, perhaps in favor of other pets that offer similar health and emotional benefits, would considerably reduce these impacts. Simultaneous industry-wide efforts to reduce overfeeding, reduce waste, and find alternative sources of protein will also reduce these impacts."

The science community has divided opinions on this topic.

Seth Wynes of Sweden's Lund University and Kimberly A. Nicholas of the University of British Columbia could not find evidence of dog ownership’s connection to climate change.

"Further research in this area would be beneficial before making environmental recommendations about dog ownership to the public," the two researchers write in the journal Environmental Research Letters. "Still, we would suggest with some confidence that a smaller dog is likely to have a smaller carbon footprint than a larger dog."

"We would suspect that cats, by extension, would have even smaller carbon footprints than most dogs," Wyne said in an interview with Forbes.