When it comes to climate change, we know where the most important warming agent — carbon dioxide — is coming from. Most of it is coming from the burning of fossil fuels, with some additional contributions from deforestation and other causes.
But the second most potent greenhouse warming agent — the hard-hitting, if short-lived, gas known as methane — presents more of a mystery. There has clearly been an alarming uptick in atmospheric methane in recent years, following a flattening of concentrations from 2000 to around 2007. But the cause of this particular pattern has been hotly debated, with some blaming the fracked natural gas boom, and others pointing to other causes, such as agriculture.
Now, new research published recently in the journal Carbon Balance and Management by three scientists with the Joint Global Change Research Institute, a center of the University of Maryland and the Pacific Northwest National Laboratory, point the finger at agriculture once again — and more specifically, at cattle and other livestock.
“Just from livestock methane emissions, our revisions resulted in 11 percent more methane in a recent year than what we were previously estimating,” said Julie Wolf, lead author of the study who completed the work while a postdoc at the institute, and now works at the Department of Agriculture. “It’s not the biggest contributor to the annual methane budget in the atmosphere, but it may be the biggest contributor to increases in the atmospheric budget over recent years.”
Cows and other ruminant animals release methane into the atmosphere as a result of a process that is called “enteric fermentation” — a technical term which basically refers to the digestive chemistry in the animals’ stomachs. As the EPA explains, the methane produced in this process “is exhaled or belched by the animal and accounts for the majority of emissions from ruminants.”
Furthermore, the animals’ waste also fills the atmosphere with additional methane depending on how it is handled, meaning that “manure management” is also categorized as a separate source of methane emissions.
The new study found that a variety of guidelines that had been introduced by the United Nations’ Intergovernmental Panel on Climate Change in 2006 to estimate methane emissions needed to be updated because livestock were being bred to be larger than before (and were being fed more), and their manure was being managed differently — more often in huge “anaerobic” waste lagoons that give off large volumes of methane.
Once the study updated the methodology, it found that for 2011, global emissions were 8.4 percent higher from enteric fermentation and 36.7 percent higher from manure management, compared with research by the IPCC.
The real question, though, is whether these changes are sufficient to account for rising atmospheric methane concentrations — something that the new study does indeed assert.