Methane emissions from animal farming in Canada, U.S. could be much higher than reported: study

Toronto -

Reported methane emissions from animal agriculture underestimate the actual level of emissions in the atmosphere, a new environmental study finds.

A joint study by New York University and Johns Hopkins University found that the bottom-up method of methane emission testing used in Canada and the United States does not properly reflect emissions in the atmosphere, meaning they could be between 30 per cent to 90 per cent higher than what is reported.

“Government agencies, like Environment and Climate Change Canada or the U.S. Environmental Protection Agency, typically use what we call a bottom-up approach or an inventory approach in order to estimate emission of greenhouse gases,” says Scot Miller, secondary author of the study and professor of environmental health and engineering at Johns Hopkins University, in an interview with CTV News.

The bottom-up approach to estimating methane gas emission involves tallying up populations of animals and determining, on average, how much methane a typical animal is producing, Miller says.

Those two quantities are then multiplied to produce estimates for total methane emissions from animal agriculture.

“An upside of this approach is that you get a really detailed process-based understanding of what processes are involved in greenhouse gas emissions,” Miller says. “People will, for example, go out and measure emissions from individual cows and understand how food sources impact emissions from cows.”

However, the study published in Environmental Research Letters, found that emission estimates produced using the bottom-up approach do not accurately record the amount of methane in the atmosphere.

“You can imagine, on the flip side of this, as you take these individual measurements and then extrapolate them to larger and larger scales, that there is a process or something that you might have missed,” says Miller.

The study found that when emission estimates from bottom-up approaches were compared to estimates produced using the more expensive top-down method of testing, there were significant discrepancies in the level of emissions reported.

A top-down approach to estimating the level of methane in the atmosphere involves measuring greenhouse gas emissions in the sky using planes, telecommunication towers and satellites, and then tracking the sources back to the ground.

“An upside of that approach is that if we can fly a plane over a landscape and measure methane across that landscape,” says Miller. “If there are emissions over that landscape there really isn’t anywhere [for it] to hide.”

However, Miller explains that the top-down approach also has some disadvantages.

“A downside of that approach is that if we use observations from an airplane that flew a kilometre above the Earth's surface, we can’t necessarily determine whether those emissions came from a cow, or a pool of manure next door,” says Miller. “We kind of only get a board-scale view of the landscape.”

Matthew Hayek, lead author of the study and professor of environmental studies at New York University, says that the most accurate estimates will use aspects of both approaches.

“It’s a combination of the two,” says Hayek. “Improving both until they hone in on the same answer. We leave room in the study that the bottom-up estimates need to come up or that the top-down emissions might also have some bias in them that needs to come down.”

Hayek says that these underestimated reports of methane emissions have international implications, as the intensive farming found in Canada and the United States has slowly become the global standard, with countries like China and others in Southeast Asia looking to adopt North American farming practices.

“The reporting of this mismatch was not available outside of specific atmospheric chemistry and physics journals,” says Hayek.

“It was not being discussed by anyone who had a hand in the international development of taking our methods of animal agriculture production, that are predominantly used in the United States, where these mismatches occur, to countries where these technologies are currently being exported, including China, much of East and Southeast Asia.”

Miller says that the next step for researchers is to get a better understanding of why these two models differ and how scientists can produce more accurate readings of methane in the atmosphere.

“I think a potentially important first step is to take more intensive observations across multiple scales in order to get a better sense of why the top-down and bottom-up estimates disagree,” says Miller. “If this disagreement is due to how we estimate emissions from manure management or how we estimate emissions from animals themselves, those different sources would imply very different things about trying to mitigate emissions.”

Hayek says that it is important for governments to acknowledge this discrepancy and work to produce a more accurate reading of greenhouse gases in the atmosphere.

“Our role as scientists here is not to condemn or support but to warn,” says Hayek, “and this was a warning and a flagging of an issue that has not received a proportionate amount of attention.”