It's long been recognised that livestock and the meat industry as a whole are a major contributor to greenhouse gas emissions responsible for global warming. But how much better off would we be if, say, everybody in the US stopped eating meat overnight?
That's the question two researchers decided to tackle in a new study, investigating just what the impacts would be on US emissions – and also American nutrition – if everybody in the country made an immediate switch to a plant-only diet.
"Our logic was to start at the extreme scenario [and work backward from that]," animal sciences researcher Robin White from Virginia Tech told Katie Langin at Science.
White and fellow researcher Mary Beth Hall from the US Department of Agriculture modelled what it would look like if all animal agriculture from American farms were eliminated, which in turn would remove all animal-derived foods from people's diets.
If such a radical plan were embarked upon, the pair calculate agricultural greenhouse gas (GHG) emissions would decrease by 28 percent – a substantial reduction, but also significantly less than the 49 percent of agricultural emissions that farm animals are responsible for in the team's model.
That's because with farm animals out of the picture, we'd then have to manage the remaining all-plant agricultural system without their ongoing help, the researchers say.
This would mean incurring a GHG burden in things like synthesising crop fertilisers to replace animal manure, and disposing of human-inedible plant waste – which is currently gotten rid of by feeding it to farm animals.
Making use of the newly additional crop land once farm animals had cleared out would also produce new emissions from plant-only farms, which are also a significant GHG contributor.
On the whole, though, making the vegan diet switch would decrease total US emissions by an estimated 2.6 percent, the team suggests, backing up previous research finding that plant-based foods have reduced environmental impacts compared with animal-based foods.
But as for what ditching all meat would do to the US population's diet, the answers aren't quite as clear cut.
While the modelling suggests total American food production without animals would be 23 percent greater than with animals – mostly thanks to increased availability of grains and legumes – from a nutrition standpoint, there'd be some serious shortcomings in terms of supply.
"With carefully balanced rations, you can meet all of your nutrient requirements with a vegetarian diet," White told Science.
"But the types of foods that seem to do that, we don't currently produce in sufficient quantities to make it a sustainable diet for the entire population."
Specifically, the researchers found an animal-free agricultural system wouldn't provide enough calcium to the US population, nor sufficient amounts of vitamins A and B12, or arachidonic, eicosapentaenoic, and docosahexaenoic fatty acids.
"Despite the production of a greater quantity of food in the plants-only system, the actual diets produced from the foods result in a greater number of deficient nutrients and an excess of energy," the authors write.
"Overall, the removal of animals resulted in diets that are nonviable in the long or short term to support the nutritional needs of the US population without nutrient supplementation."
Of course, far-reaching hypothetical modelling like this has its strengths and weaknesses, but on the terms of this research, while 100 percent veganism in the US looks like it would produce some environmental benefits, there are other problems we'd have to face at the same time.
Still, with the current outlook on climate – and the impact our current methods of farming are having on our food industry as a whole – any practice we can get in asking big questions like this is definitely valuable experience.
The findings are reported in Proceedings of the National Academy of Sciences.