Rising human population, wealth, and consumption of meat and animal products as food are likely to require that 1.5 to 2.7 million square miles (4 to 7 million km²) of land will be transferred into agriculture during the next 40 years. The rising demand for food has outstripped rising agricultural yields in recent years.  Since most of available land is found in tropical latitudes, this habitat destruction is destined to lead to the extinction of a large number of species as tropical rainforests are converted to agriculture and pasturelands.  See: http://blogs.nicholas.duke.edu/citizenscientist/harvesting-earths-bounty/.  

Numerous publications have delineated the role of diet as a major factor driving agricultural expansion. One study estimated that if all the world’s people followed dietary habits of the average U.S. citizen, 178% more land would be needed to supply the world’s food.  Adopting a diet typical of the citizens of India, who consume large amounts of grains and beans (pulses), would require 55% less agricultural land.  In particular, the production of beef has enormous environmental impacts on land, water and nitrogen cycling.  See my blog: http://blogs.nicholas.duke.edu/citizenscientist/beef-its-whats-for-dinner/.

All this brings me to the subject of this week’s blog: pets. Americans lead the world in pet ownership, which is likely to increase globally as incomes rise in the developing world.  Already, we have recognized the environmental impacts of pets: many large U.S. cities require the owners of pets to pick up pet feces that would otherwise represent a large amount of untreated sewage in runoff waters. Across the U.S. dog poop amounts to about 1/3 of the weight of human excrement. Only a fraction of this is gathered up regularly.

Reflecting their evolutionary origins, dogs and cats are natural carnivores. As a result, most pet foods—at least the tasty brands—contain animal protein.  As calculated by Greg Okin, a professor of geography at UCLA, pets consume about 25% of the meat calories consumed in the average U.S. household. For the city of Phoenix, pet food contained about 21% of the total nitrogen consumed. So, whether we look at the source of their foods, or the disposal of their waste, household pets have an enormous impact on the environment, which extends globally. 

In the United States, dogs and cats consume the dietary energy of 62 million people, which is about 20% of our population. Of course, some of the protein in pet food stems from animal parts that are not appetizing to the average American.  But, overall pets add a large demand for dietary protein in the marketplace.

Globally, provision of animal protein in foods is estimated to account for 65% of the land converted to food production. Without pets, that percentage might drop considerably. A reduction in the number of pets or in the protein we feed them would mean that less virgin land will be converted to agriculture.  Lest we forget: keeping Fido well fed extracts a toll on the natural world.

References

Alexander, P., M.S.A. Rounsevell, C. Dislich, J.R. Dodson, K. Engstrom and D. Moran. 2015.  Drivers for global agricultural land cover change: The nexus of diet, population, and bioenergy.  Global Environmental Change 35: 138-147.

Alexander, P., C. Brown, A. Ameth, J. Finnigan and M.D.A. Rounsevell. 2016.  Human appropriation of land for food: the role of diet.  Global Environmental Change 41: 88-98

Baker, L.A., D. Hope, Y. Xu, J. Edmonds, and L. Lauver. 2001. Nitrogen balance for the Central Arizona-Phoenix (CAP) ecosystem.  Ecosystems 4: 582-602.

Okin, G. 2017. Environmental impacts of food consumption by dogs and cats.  PLos One 12: doi: 10.1371/journal.pone.0181301