A professor and air quality specialist in co-operative extension in the department of animal science at UC Davis in California says the topic of greenhouse gases (GHGs) and how they affect climate is not always well understood. Dr. Frank Mitloehner took on the topic in his opening address to the Canadian Forage and Grassland Association’s annual conference last fall.
In his keynote address titled “Ruminant Livestock, Grasslands and Climate Change — Fact, Fiction and All Things in Between,” he began by reviewing the blanket of GHGs, including methane, carbon dioxide and nitrous oxide surrounding the Earth. This blanket retains a large part of the solar radiation in the atmosphere. Without it, the planet would be too cold to support life. The problem is too much GHG makes the blanket too thick and retain too much heat.
“The question now is how much do different sectors of society contribute to this greenhouse effect, and in particular for animal agriculture, how much methane, because methane is the Achilles heel of animal agriculture,” Mitloehner says.
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Measuring methane
All GHGs have a global warming potential (GWP) value which measures how effective a gas is at trapping heat. In 1990, scientists developed a system called GWP100 to show the global warming potential of the various GHGs. Mitloehner says that while it correctly showed methane to be 28 times more potent than carbon dioxide, GWP100 does not consider the removal of methane from the atmosphere when hydroxyl radicals meet methane molecules and break them down, a process that happens within approximately 10 years.
“This process is not really considered when doing the calculations with GWP100, but it should be, in my opinion, because if significant greenhouse gases are not just produced, but also destroyed, then that makes a huge difference with respect to the accounting process,” Mitloehner says, adding that this destruction does not occur with other GHGs. “It only occurs with methane, and that leads methane to be a short-lived GHG; it’s called a short-lived climate pollutant.”
Mitloehner says it’s also important to understand where the carbon in methane comes from, beginning with the creation of carbohydrates through photosynthesis. Cattle and other ruminants eat these carbohydrates, from which microbes in their stomachs produce methane. However, this is not new or additional carbon. It’s recycled carbon that was already in the atmosphere. This makes it different from other sources of GHGs such as fossil fuels, which add carbon to the atmosphere.
Mitloehner says sequestration, the process of storing carbon in the soil, also helps.
“It is believed that our soils trap and capture one-third of all human-produced carbon, so healthy soils are a very important component in our fight against climate change. Proper ranching and proper livestock handling can intensify soil carbon sequestration because by adding manure to the soil, we enhance soil microbial activity and therefore we enhance soil carbon sequestration.”
He says scientists at Oxford University have proposed a new matrix called GWP-Star, which considers the short-lived nature of methane and looks at its atmospheric removal.
“That’s very important because the world has been characterizing the impact of livestock methane on climate in a way that is significantly flawed and that needs to be rectified. If we have near constant sources of methane, and these constant sources do not add additional carbon to the atmosphere and, hence, not additional warming to our climate, and if we manage to mitigate methane, then we can pull carbon out of the air. That is a real opportunity to us.”
Success in California
Mitloehner pointed to California as a success story in reducing methane.
“In California, we have probably the most aggressive regulation on methane anywhere in the world. Our farmers are mandated to reduce methane by 40 per cent and that reduction has to happen by the year 2030, below 2013 thresholds.”
With access to financial incentives, large dairies capped their lagoons, trapping biogas, which is about 60 per cent methane, and can be used for fuel.
Mitloehner says that since 2015, dairies in California had reduced GHGs by approximately two million metric tons, with improved manure management.
“That’s incredible. I never thought it would be possible that, in just a few years, a sector as large as our dairy sector can reduce 20 per cent of its manure-based methane.
“In my opinion, in the next few years, we’ll have many more dairies jumping on to this, reducing methane and, when doing so, pulling a lot of carbon from the air,” Mitloehner says. “When you reduce methane this strongly and you’re pulling so much carbon from the air, that leads to a negative warming effect, i.e. cooling effect, that’s offsetting other GHGs that are also produced from these areas.
“Overall, if methane reductions are strong enough, then they can lead a dairy to become climate-neutral because what is pulled out of the air on the methane side offsets other GHGs, leading these operations to a point where they no longer have a warming impact.”
