If you’re looking to lower your carbon footprint, one of the best things you can do is to eat less beef or eliminate it from your diet. That’s because when cows burp, they release methane into the atmosphere, a greenhouse gas with a global heating potential of 28 to 34 times that of carbon dioxide over a 100-year period. Over a 20-year period, methane’s warming potential is 84 to 86 times as potent, according to the United Nations Economic Commission for Europe.

In comparison with other foods, beef has the highest carbon footprint by far — almost four times that of chicken and 10 to 100 times that of most plant-based foods, Our World in Data said.

Now, scientists have discovered that cows raised on grass-based diets their entire lives may have a carbon footprint that is higher overall than those that are switched to grain-based diets partway through, a press release from the Public Library of Science (PLOS) said.

“Beef production accounts for the largest share of global livestock greenhouse gas emissions and is an important target for climate mitigation efforts,” the authors of the study wrote.

Cows fed grass diets their whole lives are referred to by those in the industry as “pasture finished,” while those who are given grain before they are slaughtered are called “grain finished.”

Previous research had found that the carbon footprints of pasture-finished cattle operations were higher than those of grain-finished operations. But most studies had a limited focus regarding how much of the cattle operations’ greenhouse gas emissions came directly from beef production without factoring in other components that might affect their total carbon footprint.

“We find that pasture-finished operations have 20% higher production emissions and 42% higher carbon footprint than grain-finished systems. We also find that more land-intensive operations generally have higher carbon footprints,” the authors wrote in the study.

The study, “Carbon opportunity cost increases carbon footprint advantage of grain-finished beef,” was published in the journal PLOS One.

Daniel Blaustein-Rejto, director of food and agriculture at California’s Breakthrough Institute, and colleagues looked at 100 beef operations in 16 countries, calculating and comparing their carbon footprints. Their calculations took into account direct greenhouse gas emissions, soil carbon sequestration and “carbon opportunity cost” — carbon that would have been sequestered if native ecosystems had been left in place rather than the land being taken over for beef production.

“Most life-cycle assessments of the carbon footprint of grain-finished and pasture-finished systems have been limited to emissions directly attributable to cradle-to-farmgate activities,” the authors wrote. “Reviews and meta-analyses of these studies conclude that pasture-finished systems have higher average production emissions. Grain finishing typically leads to much higher growth rates. As a result, proportionally less energy is expended on maintenance rather than growth, such that inputs and emissions per unit of beef is lower.”

In beef operations, increased land use intensity was found to be strongly associated with a higher overall carbon footprint. The findings also suggested that, on average, carbon opportunity costs may drive up the overall carbon footprint of an operation to a level higher than its greenhouse gas emissions.

The research team said the results of the study demonstrate the necessity of climate mitigation in beef production. Making carbon footprint data available to customers would allow them to make informed choices when it comes to pasture-finished beef, for instance, which is often considered “more premium.”

“Our research reveals that the carbon cost of land use accounts for the largest part of beef’s carbon footprint. Therefore, there is an even larger carbon cost than typically found to land-intensive beef operations, such as many grass-fed systems, even when taking into account potential carbon sequestration due to grazing,” the authors added, according to the press release.

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