Not all greenhouse gases are the same, and by focusing on the properties of one in particular, we could clear cow custodians of a crumb of climate control calumny.
Dr. Frank Mitloehner is a professor and air quality specialist in Cooperative Extension in the Department of Animal Science at UC-Davis. Mitloehner is also director of the CLEAR Center, which studies the intersection of animal agriculture and the environment, to assist in making better informed decisions about what foods are eaten while reducing environmental impacts due to greenhouse gases (GHG).
Mitloehner specifically singles out methane (CH4) as the gas to focus on when considering air emissions from livestock operations. “Farmers often get a bad rap as being major contributors to global warming,” he stated.
According to the GHG guru, methane accounts for 11% of GHG emissions each year in the U.S., of which 31% is from livestock. But to better understand what that means, Mitloehner described the concept of global warming potential (GWP). GWP is a metric developed to allow comparisons of the global warming impacts of different gases. Specifically, it is a measure of how much energy the emissions of one ton of a gas will absorb over a given period of time, relative to the emissions of one ton of carbon dioxide (CO2), which has a GWP of 1.
“Methane has a GWP of 28,” he said, “so it is 28 times more heat trapping per molecule than carbon dioxide. But it would be incorrect to dismiss methane as a more dangerous GHG.”
Methane is quite different from other GHGs because it is naturally destroyed within a relatively short period of time. Carbon dioxide released into the atmosphere lasts for 1,000 years, whereas methane lasts for only 12 years. And while there is a constant source of methane produced by herds of cows, it is not greatly contributing to additional global warming because a similar amount of what is produced is also destroyed.
Mitloehner explained, “When looking at the global methane budget, what you see are various sources like fossil fuel production and use, agriculture and waste, biomass burning, wetlands and other natural emissions from lakes, oceans and permafrost. It totals roughly 558 teragrams per year. While there is a lot of time spent focusing on these sources, what’s neglected is the fact that methane doesn’t just have sources – it also has ‘sinks.’
“These sinks actually destroy methane,” he said. “Chemical reactions in the atmosphere see hydroxyl radical molecules destroy 515 teragrams of methane annually. Further sinks in soils consume 33 teragrams.”
So why does all of that matter? Because looking only at methane emission sources only gives half the picture. While there are 558 teragrams of methane emitted into the atmosphere each year, over 98% of it is broken down and destroyed by natural sinks.
Mitloehner said that if the natural sinks are protected and fostered, a methane balance could be achieved, and livestock stewards can escape the bad rap they have been saddled with.
For more information visit clear.ucdavis.edu.
by Enrico Villamaino