Easy Answer: If you consider energy consumption, the humble goldfish takes the top spot. Big dogs are the worst.
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I turned to Brenda Vale, author of Time to eat the Dog? The real guide to sustainable living, to answer today's questions. And for those dog owners on this National Dog Day, there's some bad news for you.
Here's our brief Q&A.
AH: What's the most environmentally friendly pet?
BV: The smallest vegetarian pet would have the lowest environmental impact. This is because of the land, energy and resources it takes to grow meat as opposed to grains. Thus a goldfish, even allowing for the environmental impact of the tank and the water, has the lowest impact of common pets because it is small, cold blooded, and vegetarian.
AH: What's the least environmentally friendly pet?
BV: This would have to be the largest carnivore and among common pets this would be a large dog, like an Alsatian (German Shepherd). Some people argue that dogs only eat waste meat but this is not really true as all the parts of an animal killed for food could be eaten by people, and certainly are in some societies such as those of China or other Asian countries. In the USA and other western countries mechanically recovered meat is used for things like hamburgers and frankfurters and this comes from the parts of the animal people do not normally eat (offal, brains etc).
AH: How do you determine how environmentally friendly a pet is?
BV: To do this, you undertake a footprint analysis which means looking at the land needed to grow the food and the land needed to 'grow' the energy to produce the food from its raw ingredients to the packaging to the transportation to the journey from shop to home. At the minute energy tends to come from irreplaceable fossil fuels like oil but in the future when these are gone it will have to be grown or come from renewables, which themselves take up land (think of the land absorbed in a hydro-electric scheme or a solar power station for instance).
Photo credit: Flickr user a_trotskyite.