Q: Has any individual or institution investigated the potentially disruptive impacts of the United States' close to 90 million registered dogs on our environment and wildlife? 

—Wolf in Tahoe City, California 

A: Surprisingly little research has been done on canine environmental impacts, maybe because of a certain bias toward "man's best friend." However, a recent study indicates that dogs and cats combined are responsible for around 1.5 percent of U.S. emissions of methane and nitrous oxide. Their diet alone accounts for up to 30 percent of the environmental impact from all animal production, in terms of the use of land, water, fossil fuel, phosphates, and biocides.   

Several researchers contend that dogs rank third in their ability to disturb other species, outdone only by cats and rodents. (One study revealed that even dogs piously walked on a leash scared away 40 percent of the birds as they went through an area.) Dogs have driven 11 species into extinction, and they threaten another 188, according to a 2017 study published in Biological Conservation.

The good news for dogs and cats is that there are now fewer being euthanized at U.S. shelters, down from 2.6 million in 2011 to 1.5 million annually, according to the American Society for the Prevention of Cruelty to Animals. This big reduction has been made possible by an increase in the number of adopted animals and stray animals returned to their owners. 

We still need better control of pet dogs and stronger efforts to contain feral populations. However, given our longtime affection for the critters—one estimate puts our relationship with dogs back an astounding 30,000 years—it's understandable that we are a bit reluctant to take action.