US dairies’ methane emissions down


Dairy and livestock trends in the United States indicate a decline in methane emissions. While greenhouse gas has been used by climate change activists to crush animal agriculture, science points to a different trend.

Methane as a greenhouse gas has long been the Achilles heel of campaigners to tackle animal agriculture. That seems to be changing as the scientific discovery suggests a reduction in atmospheric methane in the United States.

Frank Mitloehner, professor and air quality extension specialist at the University of California, and fellow scientists around the world are helping to change the discourse on methane. Speaking at a virtual meeting of the Alliance for Animal Agriculture, Mitloehner said that methane does not accumulate in the atmosphere like carbon dioxide, but is part of a cycle that begins and ends in the form of carbon.

Although methane is still linked to global warming and is 28 times more potent than carbon dioxide as a greenhouse gas, the science behind its creation also reveals that it is a gas of short duration which is destroyed by biological processes. The Mitloehner term used is “atmospheric absorptions”.

This was indeed the “take home” message from his presentation. Methane, while of good concern to climatologists because of its ability to raise global temperatures, is a short-lived climate pollutant that can be managed. It is also important to note, according to Mitloehner, that atmospheric methane accumulation is stable or declining in developed countries as the herd, especially in the United States, decreases.

It is only in developing countries, where herds are increasing, that methane emissions can increase.

Methane, a “ flow gas ”

Mitloehner explained it this way: Gases like carbon dioxide are a reserve gas, which means they build up over time and stay in the environment. Conversely, scientists at the University of Oxford have found that methane is a flowing gas, which means gas concentrations remain stagnant as they are destroyed at the same rate of emission. This is good news for developed countries, as trends point to a decline in the herd.

From these findings at Oxford, a new metric to assess the effects of these short-lived greenhouse gases on global temperatures has been developed. In the previous system, the effects of methane on global temperatures under constant-size herds were overestimated by a factor of four, Mitloehner said. The new metric, based on the Oxford studies, takes into account the short lifespan of methane and atmospheric removal according to Mitloehner.

For this reason, and given agreements like the Paris Climate Agreement, the goal of reducing methane emissions is achievable. In addition, this change in understanding, due to scientific discoveries, can lead to changes in global policy on greenhouse gas emissions for the benefit of livestock.

Mitloehner says animal production efficiencies already employed by US producers and similar efficiencies adopted by other developed countries are reducing methane emissions to impressive proportions. Since 2015, California dairies have reduced their methane emissions by 2.2 million tonnes per year of carbon dioxide equivalent, according to Mitloehner.

The Californian dairy industry, long accused of being insensitive to the environment due to the methane created by cows, has reduced the amount of methane created by 25%. This was achieved using methane digesters, covered dairy lagoons and a change in feed additives. Additionally, the reduction in the size of dairy herds and reduced herds in other areas means that the volume of methane created by cattle in the United States is decreasing, Mitloehner says.

Methane vs carbon dioxide

Carbon is the source of both gases. Carbon dioxide, although less toxic as a greenhouse gas than methane or nitrous oxide, enters plants that livestock consume through photosynthesis. The carbon in these plants turns into carbohydrates or starch, Mitloehner said. Hence, the cow in her example excretes methane, which after 10 years in the environment is destroyed by hydroxyl oxidation.

Conversely, carbon dioxide would remain in the atmosphere for 1,000 years.

Mitloehner is known to challenge the status quo of climate arguments that accuse animal agriculture of emitting most of the world’s greenhouse gases and therefore contributing much of the reported global warming.

This is not the case. According to the UC Davis Clear Center, 0.5% of carbon dioxide equivalent gases came from animal emissions in the United States in 2017. Eleven percent of global greenhouse gas emissions that year came from the combustion of fossil fuels, while 88% of global gas emissions came from all other sources.

Data from the United States Environmental Protection Agency shows that since 1990, total greenhouse gas emissions in the United States peaked in 2007 and have declined since. This happened while the same equivalents of agriculture, including crops and animals, remained stable throughout the period.

Methane sinks

The global methane budget – all sources produced on average from 2003 to 2012 – showed an average of 558 million tonnes from all sources. Agriculture and waste in total produced the most, followed closely by gases emitted from wetlands, at 188 million tonnes and 167 million tonnes respectively. Third place was the production and use of fossil fuels with 105 million tonnes.

Atmospheric methane removals over the period totaled 548 million tonnes per year, for a net growth rate of about 10 million tonnes, he said.

“This is still too high a number and one that we are looking to reduce further,” he said of the net increase in methane. It’s an important part of the story that there is significant removal of methane from the atmosphere. “


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