Harvard Study Finds Shift to Grass-Fed Beef Would Require 30% More Cattle and Increase Beef’s Methane Emissions 43%
A Harvard report published July 2018 in the journal Environmental Research Letters found that shifting U.S. beef production to exclusively grass-fed, pastured systems would require 30% more cattle just to keep up with current demand and production levels, and that the average methane footprint per unit of beef produced would increase by 43% due to the slower growth rates and higher methane conversion rates of grass-fed cattle. This would increase the U.S.’s total methane emissions by approximately 8%, according to the researchers.
The livestock sector accounts for more than 1/3rd of human-related methane production. Methane is especially significant because it is a much stronger greenhouse gas; in technical terms, it has a higher global warming potential (GWP) than other greenhouse gases. Using the commonly cited 100-year time-frame to measure the harmful impacts of GHGs, methane’s warming potential is considered to be between 20-28x stronger than carbon dioxide.
But with climate scientists worldwide warning that urgent action is needed to avoid the most devastating impacts of climate change, it is more appropriate to look at methane’s impacts over a 20-year timeframe— which the Intergovernmental Panel on Climate Change (IPCC) supports.
This is also important for climate goals because methane has a substantially shorter half-life than CO2, thus reducing methane emissions has a much more immediate impact on reducing global warming. Given the frequency and intensity of climate disruptions that we are now experiencing, the speed of reduction in human-caused emissions is of paramount importance.
If we look at methane’s warming effects over a 20-year time-frame, its impacts jump to 84x stronger than that of CO2. This makes the increased methane emissions of grass-fed cattle an important factor in the growing dialogue around diet and climate, especially with many sustainable food advocates urging a shift to greater production and consumption of pastured, grass-fed beef.
Increased methane emissions for grass-fed beef derive not only from the 30% increase in sheer numbers of cattle that would be needed if all U.S. beef production were to shift to pastured, grass-fed systems. It is also a result of the fact that grass-fed cattle fatten more slowly (and reach a lower slaughter weight) than grain-fed cattle, and thus take a longer time to raise.
Increased methane emissions of grass-fed cattle are also an unavoidable result of ruminant digestion, as cows fed a natural diet of grass, hay, and other forages produce three times more methane than cows fed corn and grains (the traditional diet on intensive industrial or “factory” farms.)
The study notes other environmental harms that would likely result from a shift to all or mostly grass-fed beef production, including wildlife habitat loss from greater land use, fresh water eutrophication, soil erosion, the suppression of native vegetation from overgrazing, and increased nitrous oxide emissions.
The researchers conclude, “Given the environmental tradeoffs associated with raising more cattle in exclusively grass-fed systems, only reductions in beef consumption can guarantee reductions in the environmental impact of US food systems.”
Here’s the full study: Nationwide Shift to Grass-Fed Beef Requires Larger Cattle Population.
- The Food Climate Research Network’s report, Grazed and Confused? Overview at “Goodbye— and Good Riddance— to Livestock Farming.”
- Reducing Food’s Environmental Impacts Through Producers and Consumers. Overview at “Avoiding Meat and Dairy Is ‘Single Biggest Way’ to Reduce Your Impact on Earth.”