The finding of a new paper in PNAS may ruffle the feathers of some consumers and those in the cattle industry who believe that grass-fed beef is less carbon intensive than industrial-farmed cows. Their claim arises from the idea that the grasslands on which cows graze lock in tons of CO2, which offsets the climate impacts of notoriously emissions-intensive cattle.
But when Gidon Eshel, a research professor of environmental physics at Bard College and lead author on the new PNAS study quantitatively tested this claim, he and his colleagues came up with some stark numbers. First, Eshel and colleagues took available estimates of beef cattle yields, feed needs, and methane production from herds across the United States, and then factored these into a model that allowed them to simulate and compare the emissions of grass-fed and industrially-produced beef. The researchers looked only at beef production in the US, a place where beef isn’t a necessity for nutrition.
Then they factored estimates on the carbon uptake of grasslands into the model, focusing only on US farms based in what the researchers call ‘true rangelands’ where little else can be produced. This aligned with the authors’ view that cattle should only eat what humans cannot, and should therefore not take up land that’s suited to growing crops.
Per kilo of protein, the analysis revealed, even the most efficiently-generated grass-fed beef produces between 10 and 25% more emissions than industrial beef in the US. When the researchers then incorporated the benefits of soil carbon sequestration into the equation, it did shrink this footprint—but not enough to make grass-fed any better than industrial beef. In fact this greener grass-fed beef still produces between 180 and 290 kg CO 2eq per kilo of protein, which is on balance more than the 180 to 220 kg CO2eq generated per kilo of industrial beef. Overall, the researchers found that emissions from industrially-farmed beef were lower than emissions in 90% of cases in their simulations of grass-fed beef.
Going further, they compared grass-fed beef with other protein sources, and found that pork, poultry, cheese, milk, and plant proteins produced just 5 to 35% of the emissions of the lowest-emitting grass-fed herds modeled in the study.
The higher carbon footprint of grass-fed beef stems from the way the cattle are fed, and how these animals grow, the researchers think. Grazed forage contains more lignin and cellulose, two ingredients that increase methane production in cows’ ruminant stomachs. Meanwhile, natural grass production is often seasonal, and so grazing cows’ diets are typically supplemented with resource-intensive feed like silage and hay that’s farmed elsewhere and then transported to the cows. Meanwhile, all this results in comparatively lower-weight cattle, meaning there are more emissions per kilo of protein generated by grass-fed cows, compared to industrially-produced beef.
The takeaway here isn’t that industrially-farmed beef is the better alternative, Eshel notes. People may also have other reasons to choose grass-fed beef beyond its climate impact, such as the expectation of improved animal welfare conditions compared to industrial beef. But no matter what its origins or how it was farmed, the study suggests that we should question beef as a default source of protein—especially since beef produces just 1 to 3% of the protein that plant-based alternatives do per kilo of CO2eq, the study notes.
A starting point may be to challenge the frequency with which beef is consumed in wealthy countries like the US, Eshel says: “Beef is so carbon intensive that it has no place on the list of widely used food items. Rather, the only viable role beef can play in America and developed nations’ diets is as the kind of rarity that lobsters or oysters are now.”
His parting thought for environmentally-conscious consumers? “Beef and concern for the environment are mutually antithetical. So if you cannot consume no beef, consume as little as you possibly can.”
Eshel et. al. “US grass-fed beef is as carbon intensive as industrial beef and ≈10- fold more intensive than common protein-dense alternatives.” PNAS. 2025.
Image: based on photo by Stef Bennett/Adobe Stock
Our work is available free of charge and advertising. We rely on readers like you to keep going. Donate Today