If everyone in the world went vegan, it would solve both the greenhouse gas and biodiversity problems almost overnight. Evidence shows that if people adopted entirely plant-based diets, the planet could easily support a population of 7 billion while at the same time returning huge areas of land to natural ecosystems.
Unfortunately it's not going to happen. In fact, the world is moving the other way. As developing countries emerge from poverty, they shift inexorably towards more meat and dairy-heavy diets.
So is all lost? Not necessarily. Veganism and vegetarianism are increasing in popularity in rich countries, driven by an awareness of the health, environmental and animal welfare benefits of eliminating meat. This demand reduction can be an important future contributor to more sustainable agriculture.
But if the demand side is important, the supply side is probably even more so. There are big difference in the relative environmental impacts of different types of meat, and different production systems. Poultry, for example, is lower impact than pork, which in turn is lower impact than beef.
Beef is the big one, accounting for 41 percent of livestock sector emissions. Livestock production already uses about a third of the global land area, and cattle grazing expansion contributes to deforestation in high-priority conservation areas like the Brazilian Amazon.
Many meat connoisseurs in America choose grass-fed steaks, but actually this is — environmentally speaking — the worst option of all. In terms of land use, which is the metric that matters most for conservation, extensive (grass-fed) beef uses 15-20 times as much land as intensive feedlot cattle operations. The figures for greenhouse gas emissions are less dramatic but still better for intensively-reared beef.
So does that mean you should ask for a factory-farmed steak next time you eat out? Clearly there is a trade-off, as Marian Swain and co-authors from the Breakthrough Institute and Oregon State University describe in a new paper entitled “Reducing the environmental impact of global diets” (open access). So-called CAFOs (confined animal feeding operations) can also be heavy on the use of antibiotics, create pollution from manure lagoons and raise serious concerns about animal welfare.
These trade-offs are real and raise difficult moral issues. Which is more important — animal cruelty or the climate? But the authors also show that there are synergies as well: finishing cattle on grain does not necessarily reduce welfare, and can be a much more efficient way of getting beef cows to market weight with less feed.
"Intensification practices like selective breeding and modern veterinary care can dramatically improve productivity, especially in developing countries where livestock are often smaller and sicker than animals in industrialized countries," Swain and her colleagues write. Perhaps more controversial is their suggestion that "intensive production, including in CAFOs, can be responsibly managed to minimize animal stress and contain environmental impacts, but policies are necessary to ensure best practice is followed."
Swain et al conclude: "Modern, intensive livestock systems can reduce the land use and GHG emissions of meat production, most dramatically for beef. This offers an important opportunity to achieve land sparing and reduced emissions even with projected increases in meat demand."
There is an important final caveat, however. Shifting to more land-intensive diets does not by itself spare land for re-wilding or conservation. Achieving this end requires active policy intervention, such as zoning large areas — ideally of the least fertile land — for conservation or wildlife reserves.
One proposal that has begun to gain support internationally is the idea of “Half Earth” — the concept that humans should set aside 50 percent of the land and oceans for nature. According to conservationists, this would protect 85 percent of species from extinction — a worthy aim for sure.
But “Half Earth” is a fantasy unless we can get a grip on global diets. That will require both getting people to eat less red meat, and also producing the meat that people do consume on the smallest area of land possible. That might mean abandoning some of our sacred culinary cows — such as a preference for grass-fed beef — in the process.