For more than a decade, the global concentration of methane — a pernicious greenhouse gas 86 times more potent than carbon dioxide over a 20-year period — has been rising at an alarming rate, stirring up intense debate in the scientific community over the cause of the increase. Now, a new study adds to a growing body of evidence suggesting the spike can largely be traced back to gas production — but from livestock, not the fossil fuel industry.
The study, conducted by scientists with the Joint Global Change Research Institute and published in the journal Carbon Balance and Management, found that previous estimates of the global livestock industry’s methane production had been underestimating the total by about 11 percent. And while livestock emissions aren’t the biggest overall source of methane — past studies have pointed to the oil and gas industry, especially fracking, as a major source of methane — the study suggests that animal agriculture could be responsible for the recent increase in methane concentrations. After remaining relatively flat for decades, global methane levels have increased from roughly 1750 parts per billion in the early 2000s to around 1830 parts per billion — a faster rate of increase than at any other time in the last twenty years.
“Our results suggest that livestock methane emissions, while not the dominant overall source of global methane emissions, may be a major contributor to the observed annual emissions increases over the 2000s to 2010s,” the study concludes.
Livestock — mainly cows, but really any ruminant that breaks down food in the first of four stomachs, essentially fermenting food that normal digestive acids can’t handle — produce methane as a byproduct of digestion, and they have been releasing this gas into the atmosphere since before humans domesticated farm animals tens of thousands of years ago. But in recent years, especially, as developing countries like China and India have fueled an increase in global demand for meat, livestock production has undergone some serious changes. Meat production in the developing world tripled between 1980 and 2002, which means changes in the amount of livestock-related methane gets released into the atmosphere each year.
The study’s authors — whose work was sponsored by NASA — tracked the changes by looking at methane emission estimates from the 2006 Intergovernmental Panel on Climate Change (IPCC) report. In reviewing the data, they realized that the 2006 report did not take into account a few crucial changes in both livestock breeding and management — the facts that cows are being bred to be larger and that their manure is largely stored in massive pits, known as lagoons, that give off methane. When those changes were factored in to the 2006 data, the study found that, globally, estimated emissions from livestock digestion went up 8.4 percent, and estimates for manure management went up 36.7 percent.
“In most developed regions, the livestock have been bred to be larger — they are more productive, especially with dairy cows,” Julie Wolf, lead author of the study, told the Washington Post. “And that will result in a larger estimate of methane emitted by each animal.”
Past studies have also pointed to agricultural-related emissions, rather than fossil fuel emissions, as being primarily responsible for the increase in methane over the past decade. One study, published in 2016, used isotopic signatures — the ratio of various carbon isotopes — from monitoring stations around the world to conclude that methane produced from agriculture had been increasing more rapidly than methane produced from fossil fuel extraction like fracking. That study pointed not only to livestock production, but also rice farming, which produces methane when rice fields are flooded during irrigation, creating an environment for bacteria to feed off of carbohydrates created by the rice plant’s root. When bacteria digest those carbohydrates, they release methane, in the same way that cows or sheep produce methane in their digestive tracks.
Still, the scientific community is hardly uniform in its understanding of where the recent spike in methane emissions is coming from. Other studies have seemed to pinpoint fossil fuel production — especially hydraulic fracturing — as the primary source of the increase in methane, including one study that found that the methane leaks associated with natural gas production effectively offset any climate benefit of switching from coal to natural gas. The Obama administration attempted to set limits on the amount of methane that oil and gas producers could allow to escape during fossil fuel extraction and processing, but the Trump administration is currently delaying implementation of those rules.
To tackle the issue of livestock-related methane emissions, studies have suggested various solutions, from feeding livestock seaweed (which in one study reduced methane production by 70 percent) to giving livestock special supplements aimed at curbing methane production in a ruminant’s digestive cycle (one study found it cut production by 30 percent). Some countries have also updated their dietary guidelines to limit meat consumption — though when a nutrition advisory committee suggested the United States do something similar, the meat lobby sprang into action, voicing staunch opposition to the idea. And their opposition appears to have worked: meat restrictions were not included in updated dietary guidelines released in October of 2015, and that same year, meat consumption in the United States increased at a faster pace than anytime in the past 40 years.
Despite being a major source of methane emissions in the United States (manure management and livestock digestion account for over a third of U.S. methane emissions, according to the EPA), the livestock industry has largely been exempted from government attempts to regulate greenhouse gas emissions. Congress actually explicitly prohibits the EPA from collecting emissions data from the livestock industry, making it the only major U.S. industry to enjoy such an exemption.
In California, which is jockeying to be both a leader on climate change and a leader in the U.S. dairy industry, the state government has taken small steps towards regulating methane production, asking the state’s Air Resources Board (ARB) to come up with a plan to regulate methane emissions from livestock. But with the Trump administration’s desire to make regulation more industry-friendly — and EPA Administrator Scott Pruitt’s cozy relationship with the cattle industry — it’s unlikely that the federal government will undertake a similar effort.