Domestic animals have played a significant role in the history of human civilisation. Ever since the end of the last ice age, humans have cultured a relationship with the surrounding fauna for their benefit. Today's pets are the product of generations of selective breeding. We allowed those with characteristics we liked to flourish. So far, so useful.
But as new technology mechanised many processes, some domesticated animals were increasingly valued for their companionship, rather than practicality. Domesticated cats who once devoured rats to keep the pests and the accompanying disease at bay, became reliant on the food that owners provided. Many domesticated animals have essentially become living toys, existing to entertain their owners.
So what, you might say. Well, with the combined global population of cats estimated to be between 200 and 600 million, and dogs upwards of 500 million, it would be interesting to know how much is invested in producing their food. In an age where climate change and resource scarcity are pressing issues, should pets be considered a luxury we could do without? Should we be implored to think twice before acquiring yet another methane-producing, meat-consuming, live-in monster? Can we afford to keep pets if it's going to cost us the Earth?
Professor Brenda Vale, of Victoria University, New Zealand, thinks not: "We shouldn't be keeping pets in the numbers they are currently kept in. It's unreasonable to have the idea that you can have it all— children, two large dogs and an SUV—and somehow it doesn't matter." In fact, Vale finds many aspects of modern life so concerning that she authored Time to Eat the Dog?: The Real Guide to Sustainable Living. The book swims in numbers and calculations as it attempts to quantify the impact of various parts of modern living, and aims to encourage people to shake habits cultivated over centuries.
It is of course well-documented that our global way of life is entirely unsustainable. The World Bank-commissioned report on Climate Change in 2012, "Turn Down the Heat: Why a 4° Warmer World Must be Avoided", states that our current trajectory will be "devastating" and averting our current course is "vital for the health and welfare of communities around the world". If everyone lived like an average American citizen, we'd need at least four Earths to support us.
So how can one compare the impact of an animal to a car? Talking about energy usage can be abstract and intangible. Mathis Wackernagel and William Rees of the University of British Columbia, Vancouver, developed the idea in the 1990s of an "ecological footprint", and with it the "global hectare". They employed a beautiful, simple unit we can relate to: the surface of the Earth. Apart from very few isolated incidents (a new volcano creating an island, for instance), the total biologically productive area on Earth is basically an unchanging value over time. It's essential that we have enough space to produce the resources that support our needs. If this ceases to be the case, life becomes unsustainable and we're just sailing a sinking ship on an acidic sea through the mists of CO2.
The global hectare (gha) represents a plot of land 100m by 100m, about the area occupied by a football pitch. In the words of the Global Footprint Network, it is a "productivity weighted area used to report both the biocapacity of the Earth, and the demand on biocapacity". For keen number crunchers, each global hectare is capable of producing 135 billion joules of energy per year. The global hectare idea essentially averages out the entire productivity of the Earth over its surface, offering one neat metric.
With the current population of the world at 7 billion, and the approximate 12 billion hectares of biologically productive land and water surface available, we can calculate that a "fair Earth- share" for each human being would be around 1.7 gha. Against this benchmark, we can see whether different societies are using over or under their fair share. To illustrate the contrast, the average American citizen in 2011 (the most recent dataset available) had a footprint of 6.5 gha, with Filipinos clocking in at 1.0 gha.
Performing these calculations for domesticated animals yields some shocking results. For example, it is calculated that an average Alsatian requires 0.36 gha of land. According to the New Scientist article "How Green is Your Pet?", that is a larger ecological footprint than an average household diesel car. Cat-lovers are hardly off the hook, with an indoor feline clocking in at 0.15 gha. Six cats create equal demand on the earth to one Indian human: 0.9 gha.
Using the aforementioned figures for global cat population (400 million is somewhere in the middle of existing global estimates), they would have a total ecological footprint of 60 million gha. Performing the same calculation for dogs, pretending all are medium-sized (requiring 0.27 gha), we get 135 million gha for the domestic canines. This gives a combined total of 195 million gha. If that means absolutely nothing to you, which it likely won't, then think of it as the combined total ecological footprint of a city-based population of 150 million people. If these dogs and cats disappeared, it would be the same as if twice the population of the UK did the same, in terms of ecological impact.
Remember, this is just dogs and cats. If you prefer, this is the same ecological footprint as over 475 million Toyota Land Cruisers driven 10,000km a year, equivalent to nearly twice all the cars in the USA.
But can we trust these calculations? Professor Ralf Toumi, head of the Space and Atmospheric Physics group at Imperial College, London, told me: "I think most of the carbon footprint [of pets] comes from buildings, and diet is non-negligible. So, if meat-eating pets live with humans, then it is conceivable [that these figures add up]."
If we accept the calculations that Vale's book presents, the next question is, do we care enough to do something about it, and if we do, where do we start? One option is sharing currently-owned pets between small communities. Vale proposes that humans should not rely on animals for their social interaction: "We need to make sure, in our high-density environments, that everyone belongs to a small community within the whole, so that friendship and support come from people first. Once these groups are established, then it becomes easier for, say, one single person, to have care of a pet that children can interact with, feed, take for walks and so on."
Alternatively, we could keep smaller animals, like goldfish or canaries. These are by their nature harder to share, but their ecological footprint is minuscule compared with larger animals. An Alsatian has the same ecological footprint as 1,059 goldfish.
There are more controversial ideas. One of these is to promote owning edible domestic animals, rearing pets with a view to eating them. Other ideas include a one-child policy for domestic animals, which Professor Vale called an "excellent idea". Vale has already tried to implement rules allowing only edible pets in her local area of Wellington, New Zealand. At the most extreme end of the scale of reactions, we could even make a concerted effort for this generation of pets to be the last, spaying and neutering all currently alive.
Is this where the normally harmonious concerns of sustainability and animal welfare proponents turn against each other? Claire Drake, UK representative of People for the Ethical Treatment of Animals (PETA), argues that we are thinking in the wrong way about animals and meat. She states that "the impact of dogs and cats on the environment when compared to the impact of the meat, egg and dairy industries is minuscule". She suggests we need to include all livestock that has been selectively bred for food (cows, chickens, pigs and so on) in the debate, and the figures. Rather than talk about how we can raise domestic animals to eat them, we should simply forego meat altogether.
Drake indicates that this is the real issue: "Going vegan is one of the most effective ways to fight climate change. A staggering 51 percent or more of global greenhouse-gas emissions are caused by animal agriculture, according to a report published by the Worldwatch Institute. Additionally, a United Nations report concluded that a global shift towards a vegan diet is extremely important in order to combat the worst effects of climate change." In 2014, raising animals for slaughter and diary products emitted more green- house gases than all global transport, according to the Chatham House report, "Livestock—Climate Change's Forgotten Sector".
We have several options available ranging from the gently inconvenient to the radical: halting reproduction of pets, counting all livestock as domesticated and then facilitating their extinction, while becoming vegan en masse. If you had to choose between your car or your cat, what would you do? Commendable as it is to forego our car commutes into work for a bike ride, will it really make much difference if you keep five cats? If we are serious about sustainability and climate change, it may soon be a hard time to be a domestic animal. If we're not, it may soon be a shitty time to be human.