Grass feeding produces more greenhouse gases than feedlot beef because of increased fermentation in the gut, research concludes.
- Grass-fed cows produce more greenhouse gas than grain-fed.
- Critics point out that the pasture used to raise grass-fed beef offers a carbon sink.
- Experts point out that eating vegetarian is far better from a carbon point of view.
Red meat has a bad reputation among the green-minded for its emissions of heat-trapping gases that exacerbate climate change. Fertilizer derived from fossil fuels is required for growing grain to feed cattle, and cows' digestion produces large amounts of the potent greenhouse gas methane, which is 25 times more heating than carbon dioxide.
But a new study of the Australian livestock industry finds that the seemingly greener alternative to grain-fed beef -- beef from cows grazed on grass -- produces more greenhouse gases per pound than beef from feedlots.
"The reason for that is that, on the one hand, the grain-based diet can be digested better by the animals, so that reduces the enteric methane production by the animals," said study lead author Matthias Schulz of the University of New South Wales Water Research Center in Australia.
Grain-finished beef produced 38 percent less methane, the researchers found, though other studies have reported as much as 70 percent less.
"Also, although the (total) emissions are higher on the feedlot, the animals gain weight quicker," Schulz said, so the animals are slaughtered sooner, emitting less gas overall. "On a per-kilogram-of-meat basis, the feedlot performs better," he said.
Emissions from grass-fed cows were about 20 percent higher than grain fed, according to the study, which was published in Environmental Science and Technology, and funded by Meat and Livestock Australia.
Schulz' study also concluded that raising sheep produced less greenhouse gas emissions than beef, largely because the animals have about half the lifespan of cattle.
Other studies have made the same comparison between beef from grass versus grain-fed animals and found that the higher methane emissions from grass-fed cows tip the carbon scales in favor of feedlot beef.
But some people claim that the math comes out the opposite way if carbon stored in the soil by grazing animals is incorporated: Grass-fed beef mow the pastures, fertilize the ground with their manure, and tramp around, creating healthy soil that acts as a carbon sink.
If the carbon storage is incorporated, they claim, grass-fed beef produces no net emissions, and can even capture carbon overall.
The problem, said Christopher Weber of Carnegie Mellon University, is that accurately quantifying how much soil carbon contributes is difficult, and it can vary dramatically from place to place -- even in locations just a few feet away. This uncertainty can swing the calculation one way or another.
To Weber's knowledge, no study published in a scientific journal has come to the conclusion that grass-fed beef is better from a greenhouse gas perspective.
"There's a lot of range of what the emissions are from beef, and that is real variability," agreed Rita Schenck, Executive Director of the Institute for Environmental Research & Education in Vashon, Wash., who has also studied this question.
"It is different in different places. It is different in different growing regimes. It's just different. I think the numbers are really close," she said, so the scales can tip one way or another depending on the specific circumstances.
"To some extent, all of this bickering about carbon footprint is missing the forest for the trees," Weber said. ""In terms of air pollution, water pollution and odor, concentrated feedlots are a disaster. In terms of other environmental impact, there is no question that grass fed is better. My problem is that people really play on the carbon footprint angle, when it's really not clear. "
According to a 2006 United Nations report, livestock accounts for 18 percent of the world's greenhouse gas emissions.
Grass-fed cattle require fewer antibiotics and other chemicals than grain-fed cows, and the resulting beef is higher in healthy omega-3 fatty acids.
"The take-home message," Schenk said, "is that no matter how you grow the beef, eating vegetarian is substantially better from a carbon point of view."