Vegetarianism and Wild Animals
Summary. It has been argued that promoting vegetarianism increases the number of animal life-years that exist because the reduced ecological footprint of the vegetarian diet allows many more animals to exist in the wild. This may not be true if climate change would have increased the number of wild animals that exist over the long term, so I remain uncertain about the net impact of vegetarianism on wild-animal life-years. However, if it is the case that vegetarianism results in a net increase of wild-animal life-years, and if wild animals suffer more than they're happy, then the widespread assumption that adopting a vegetarian diet prevents animal suffering might be wrong. However, even if this were so, the activities of organizations like Vegan Outreach could still be on balance beneficial, by encouraging people to care more about animal welfare in general.
Introduction
Animals raised in factory farms suffer enormously. Vegetarians aim to prevent this suffering by reducing the number of factory-farmed animals that exist. While many agree that this is a noble goal, the so-called Logic of the Larder
claims that vegetarianism actually does a disservice to factory-farmed animals by denying them the chance to live.
Vegetarianism and Farm Land
Gaverick Matheny and Kai Chan respond to this charge in an excellent paper, Human Diets and Animal Welfare: the Illogic of the Larder.
Suppose it were true, they suggest, that factory-farmed animals had lives worth living. Even in that case, those who want to create more happy animals should promote vegetarian diets because such diets allow more wild animals to exist. This is because less farm land is generally required to produce vegetable protein than factory-farmed animal protein, and the unused farm land supports greater abundance of wild-animal life than if it were cultivated. In particular, Matheny and Chan calculate that switching from a typical American omnivorous diet to a vegetarian diet causes a net increase of 0.6 animal life-years, counting both farmed and wild animals (pp. 586-587).
On pp. 587-588, Matheny and Chan note reasons that this figure may easily underestimate the increase in life-years that vegetarianism causes, perhaps by several orders of magnitude. One of the most important is that the authors counted life-years only for mammals and birds, since other taxa -- reptiles, amphibians, fish, and especially insects -- are less than certain to be sentient. This served to make their figures conservative, but a better utilitarian analysis for decision purposes would assign some probability to the sentience of these other organisms and include them accordingly. Doing so would, I think, cause wild-animal life-years to dominate the calculation. To see this, consider that the wild-animal densities Matheny and Chan used were on the order of 103 per km2 (p. 585), while arthropod densities are on the order of 108 per acre, or 1010 to 1011 per km2.[1] Even if we assigned an extremely low probability to arthropod sentience (say, 10-3 or 10-6), the expected densities would still be orders of magnitude higher than those for mammals and birds.
Potential Relevance of Climate Change
In addition to freeing up farm land, vegetarianism has another major environmental impact: Reducing greenhouse-gas emissions. Eating a vegan diet instead of a conventional omnivorous American diet results in 1.5 fewer tons of CO2-equivalent gases per year. Assuming total emissions of 31.0 billion metric tons = 34.2 billion tons of CO2 by 2010 (see Figure 9 here), 1.5 tons represents a fraction 4 * 10-11 of all human contributions to climate change in a given year.
On p. 587, Matheny and Chan acknowledge that their analysis omits externalities of agriculture like its contribution to global warming. However, the effect could be significant. To see this, suppose for illustration that global warming, say, increased the total animal population of the planet by 10%. Let's work just with mammal and bird populations to keep the figures comparable to those in the Illogic
piece. A naïve estimate for the earth's total mammal-and-bird population based on Matheny and Chan's numbers would be something like (103 individuals per km2) * (1.5 * 108 km2 of land on earth) = 1.5 * 1011 individuals, so that a 10% increase represents 1.5 * 1010 individuals. Assuming that one year of greenhouse-gas emissions causes only one year of increased wild-animal populations and that the increase in animal populations due to global warming is a linear function of the amount of CO2-eq emitted, a vegetarian diet would -- by attenuating climate change -- reduce wild-animal life-years by (1.5 * 1010) * (4 * 10-11) = 0.6, which is on the same order of magnitude as the changes due to agricultural land use, but in the opposite direction.[2] Thus, an adjustment in one of the input figures of an order of magnitude or two could flip the calculation around.
Will Climate Change Result in More or Fewer Wild Animals?
Of course, above I supposed that climate change would on the whole increase wild-animal populations, but this is far from obvious. Some of the consequences of global warming do suggest such a trend, including the following:
However, other consequences of climate change will reduce the number of animals living in the wild. For instance:
There is no shortage of information on specific effects of climate change on various ecosystems, species, and biome patterns; e.g., Chapter 4 of the IPCC Fourth Assessment Report is a great place to start. On the other hand, it's easy to get bogged down in noisy point estimates and lose sight of the big-picture factors to consider. It may be that just one or two of the impacts of climate change dominates the others in the analysis -- what might those impacts be?
Might Vegetarianism Increase Animal Suffering?
For purposes of responding to the Logic of the Larder, Matheny and Chan grant the assumption that animal life-years have positive value. However, they note in a footnote on p. 586 that arguments have been made that neither set of animals [in factory farms nor in the wild] has lives worth living – their lives are filled with more misery than happiness (Ng, 1995). In this case, it would be best to adopt a diet that results in the fewest number of animal life-years.
I share Ng's concern that wild-animal lives may be on balance negative. But if this is true, then promoting vegetarianism may cause more suffering than it averts -- unless consideration of climate change tilts the balance, as the above analysis suggested that it might. For this reason, I would be very curious to learn more about the wild-animal impact of climate change -- as well as other factors I've neglected to consider -- and I encourage readers to email me with comments.
Promoting General Concern for Animals
Even if vegetarian diets do increase animal suffering by creating more wild animals, it doesn't necessarily follow that organizations promoting vegetarianism do more harm than good. Exposure to the cruelties of factory farming is one way in which many people are first introduced to the topic of animal suffering in general, and one hopes that such concern might spill over into other domains, perhaps including suffering in nature. After all, if animals on factory farms would be better off not existing, then if conditions in the wild are for some animals just as miserable, then those animals would be better off not existing as well. And whether or not wild-animal lives are on the whole painful, it may be possible -- perhaps much farther off in the future -- to improve their welfare just as is done for farm animals, such as through more humane slaughter by predators.
General concern for animal suffering is crucial if humans are to make wise choices with respect to wild animals when they develop more advanced technologies, and utilitarian promotion of vegetarianism seems generally likely to cultivate such sympathies.[4] Of course, raising awareness explicitly about animal cruelty in nature may be more effective -- and less potentially costly in its direct impact on suffering in the wild.
[1] One source mentions an estimate of 425 million arthropods per acre in forest. This paper cites estimates around 100-200 million per acre for crop land.
[2] I say only same order of magnitude
because the 0.6 net life-years that vegetarianism creates when climate change is ignored counts farmed animals as well as wild animals.
[3] Figure 8 of this study reports increases in dry-matter production (DMP) generally between 0% and 30%. I would guess that more plant biomass usually implies more animal biomass because there's more food to be eaten, both by herbivores and decomposers. However, it's important to consider specific floral changes on a case-by-case basis; for instance, even though algae may grow faster with higher CO2 concentrations, they could also become less nutritious.
Also keep in mind that higher CO2 concentrations is an effect of emitting CO2 directly, rather than climate change generally, and a significant fraction of the global-warming contribution of meat comes from non-CO2 greenhouse gases like methane and nitrous oxides. Still, a vegetarian diet does produce less raw CO2 due to lower energy consumption, to the tune of about 0.7 metric tons per person per year (p. 10 here).
[4] On the other hand, promoting vegetarianism from, say, the perspective that humans have no right to interfere with animals could be counterproductive.