Since 2006, atmospheric levels of methane — a greenhouse gas 86 times more potent than carbon dioxide over a 20-year period — have steadily been on the rise. For years, scientists weren’t sure what was behind the rising levels of methane, but they had a few ideas: namely an increase in fossil fuel-related emissions.
Now, a new study is pointing to a different culprit: agriculture-related methane emissions, especially from livestock and rice production.
Published last week in the journal Science, researchers from New Zealand’s National Institute of Water and Atmospheric Research (NIWA) found that the majority of methane released into the atmosphere since 2006 was produced by bacteria, pointing to sources like agriculture — rather than sources like fossil fuel production or the burning of organic material — as the culprit behind the increase in methane levels.
A unique signature for methane
The researchers were able to discern agricultural methane from other sources of methane by looking at the gas’ isotopic signatures — or the ratio of various carbon isotopes — using data from atmospheric monitoring stations around the world. By looking at the distinct isotopic signatures, the researchers could differentiate between methane produced from fracking, for instance, and methane produced from agriculture, because they each have different signatures.
The data also suggested that the increase in methane came from regions including India, China and Southeast Asia, suggesting that the rise was due to agriculture, not the growth of fracking in North America.
“That was a real surprise, because [around 2006] the U.S. started fracking and we also know that the economy in Asia picked up again, and coal mining increased,” NIWA atmospheric scientist Hinrich Schaefer told Phys.org. “However, that is not reflected in the atmosphere.”
Livestock production in Asia has been expanding rapidly since the middle of the 20th century, and is expected only to increase as economies in the region become more developed.
Livestock production accounts for about 35 percent of total anthropogenic methane emissions
Around the world, livestock production has been increasingly under scrutiny in recent years, as animal agriculture’s carbon footprint has grown clearer. Ruminants, like cows, produce methane as they digest their food, through a process known as enteric fermentation. But livestock manure also produces methane as it decomposes in closed-air containers known as lagoons, which factory farming operations often use to store the massive amounts of manure produced by their farms. The United Nations’ Food and Agriculture Organization estimates that livestock production accounts for some 2.2 billion tons of carbon dioxide equivalent greenhouse gases annually, or about 35 percent of total anthropogenic methane emissions.
But it’s not just livestock production that researchers say is behind the rise in methane. Rice production is also a methane-intensive activity, because root systems in rice plants secrete carbohydrates during photosynthesis. When rice paddies are flooded, the oxygen-devoid environment creates the perfect place for bacteria to feed off of those carbohydrates, creating methane as a byproduct. That’s a problem, because rice is one of the most important staple crops on Earth — more than 3.5 billion people depend on rice for at least 20 percent of their daily caloric intake. In an effort to curb rice’s methane production, scientists have actually been working to create a lower-methane strain of rice (and have had some success).
But what about fossil fuels?
Still, not everyone is convinced by NIWA’s analysis. Speaking with InsideClimate News, Robert Howarth, a Cornell University professor who studies methane emissions, said that the isotopic ratios in methane are too broad to confidently attribute to a single source.
“When you have eight or nine or 10 different sources of methane, each with a range of ratios, there is no way to calculate where it is coming from,” he said. “If you had a little bit of melting of permafrost and a big increase in natural gas production, you could get a pattern that these people are interpreting as cows in India.”
Many other studies point to an increase in fossil fuel production, especially oil and gas production in the United States, as another key factor behind the recent increase in methane production. A recent study conducted by climate scientists of Karlsruhe Institute of Technology (KIT) found that as much as 40 percent of the recent increase in methane could be due to fossil fuel production.
In a press release, the KIT scientists said that their findings were actually congruent with the NIWA study, stressing that “increasing emissions from the oil and natural gas sector, combined with emissions from wetlands and maybe animal husbandry increasingly appear to have caused the renewed increase in methane concentration in the last decade.”
An unregulated industry
The Obama administration has taken some unprecedented steps in the recent months to regulate methane from oil and gas production. Most recently, the EPA announced that it would begin regulating methane from existing oil and gas facilities, with the ultimate goal of cutting methane from the oil and gas sector by 40 to 45 percent below 2012 levels by 2025.
But methane from the agricultural sector is still largely unregulated, despite the fact that greenhouse gas-related emissions from livestock manure management systems grew 54 percent between 1990 and 2013.
Quite the opposite of imposing regulations on livestock producers in the United States, Congress has actually explicitly forbidden the EPA from collecting greenhouse gas emission data from livestock producers, making it the only major source of greenhouse gas emissions in the United States that enjoys such an exemption.
“The EPA’s methane strategy is completely ignoring agriculture,” Tarah Heinzen, an attorney with Food & Water Watch, told ThinkProgress. “We’re not dealing with it as a regulatory issue as we are with other sources of methane.”
Decarbonizing what we eat is just as important as decarbonizing what we drive or what we use to heat our homes
California, which is one of the most livestock-heavy states in the country, has made moves to begin regulating short-lived climate pollutants, like methane. According to Brent Newell, legal director for the Center on Race, Poverty & the Environment, methane from livestock accounts for about 5 percent of California’s total greenhouse gas emissions. The state’s Global Warming Solutions Act, passed in 2006, mandates that the state reduce its greenhouse gas emissions by 20 percent — and yet agriculture is the only sector not subject to regulation.
In 2014, the California Senate mandated that the state’s Air Resources Board (ARB) come up with a plan to regulate methane from livestock operations. But thus far, the ARB has decided to achieve reductions only through voluntary measures, which Newell argues allows the livestock industry to effectively continue with a business-as-usual approach to methane production.
“It’s acting like it’s doing something, it’s pretending like it’s doing something, but voluntary controls for a massive greenhouse gas emitter is a crazy regulatory response and it exemplifies the political power that the dairy industry has over the Air Resources Board,” Newell said.
The plan is expected to be finalized later this month, when it will be seen whether environmental groups’ calls for mandatory regulations for the California livestock industry have been heard by the ARB, or whether such calls have fallen on deaf ears.
“It is really shameful that this industry continues to enjoy an exemption, while others are forced to comply,” Newell said. “Decarbonizing what we eat is just as important as decarbonizing what we drive or what we use to heat our homes.”