GWP* and cattle: Cows feeding at sunset
Livestock’s Path to Climate Neutrality Starts With Rethinking Methane

How GWP* can help us find a climate solution with cattle

Beef Cattle GWP*
Credit: CLEAR Center at UC Davis

By Frank Mitloehner

There’s no denying the unprecedented glut of carbon dioxide hanging in the atmosphere. As organizations and individuals debate what to do about it, one of the solutions might be right before our eyes. Though methane is frequently presented as a fearsome greenhouse gas, especially when it’s emitted by cattle, research suggests we need to begin looking to it for its potential to have a cooling effect.

Lest I lose anyone, let me say at the outset that I believe it’s crucial that we don’t increase the methane we’re putting in the atmosphere. That will only exacerbate the problem of climate change. Methane is a potent greenhouse gas, with 28 times the global warming potential of carbon dioxide over a 100-year period. That’s according to the current GWP100 measuring standard that, in an attempt to level set all greenhouse gases, equates each one to a kilo of carbon dioxide over a 100-year period.

But GWP100 doesn’t fully describe methane’s impact on the climate. It is not simply an amped-up version of carbon dioxide, the most plentiful – and over the long term, most powerful – greenhouse gas in our atmosphere. As a matter of fact, methane behaves very differently from carbon dioxide, making the GWP100 calculation misleading at best.

A miss in the GWP100 calculation

We care about greenhouse gases, because they warm our climate. But we do not always measure them by how much warming they are actually causing. The GWP100 accounting was established back in 1990 and for a good reason. That is, to standardize the impact of each greenhouse gas in order to allow us to draw comparisons. The problem is, GWP100 is simply measuring methane’s carbon dioxide equivalence (CO2e) and overlooking how methane warms the atmosphere. That’s a significant oversight.

How methane warms our planet and contributes to climate change

Biogenic methane is a short-lived climate pollutant (SLCP) and a flow gas ­– meaning it is destroyed at the same rate it is emitted – with a half-life of roughly 10 years. In that time, it reacts with a hydroxyl radical to create carbon dioxide and water.

As part of the biogenic carbon cycle, plants absorb carbon dioxide, and through the process of photosynthesis, they harness the energy of the sun to produce carbohydrates such as cellulose. Undigestible by humans, cellulose is a key feed ingredient for cattle and other ruminant animals. They are able to break it down in their rumens, taking the carbon that makes up the cellulose they consume and emitting a small portion as methane. After 10 years, the methane is converted into carbon dioxide. Such is the cycle. 

Biogenic Carbon Cycle Cattle Methane
Credit: UC Davis CLEAR Center

Carbon dioxide from fossil fuels is a far different animal, so to speak. It’s a long-lived climate pollutant (LLCP), a gas that keeps building up in the atmosphere, adding to the existing stock – hence the designation. By conservative estimates, carbon dioxide stays there for 1,000 years. Potentially, forever. That’s because there is far too much of it to be taken out by carbon sinks, the oceans, soils and plants. Blame humans, not cows, for that. Our love affair with the burning of fossil fuels is not cooling down. Consequently, neither is the atmosphere.  

Methane could help solve the problem of global warming

As counterintuitive as it may seem, methane could well be part of our solution to the problem of climate change. In other words, it can act as an atmospheric coolant, providing we are able to reduce our emissions. However, you wouldn’t know it when using GWP100.

To prove the point, scientists from Oxford are suggesting a different greenhouse-gas metric called simply “GWP*.” Instead of measuring one methane pulse emission against a same-size pulse emission of carbon dioxide, Myles Allen and his team of researchers are suggesting a more reliable approach that takes into consideration the differences in how SLCPs and LLCPs react in the atmosphere. That is, to measure the increase in the emission rate of methane with a single pulse emission of carbon dioxide. Under the guidelines of the GWP* standard, one could more accurately compare the effect of adding a cow to one’s herd (and thus, an increase in methane), to a single pulse emission of carbon dioxide from the burning of fossil fuel, for example.

Their conclusions are stunning. Using GWP*, the following set of graphs shows what happens when carbon dioxide and methane emissions: 1) rise; 2) remain constant; and 3) decrease.


GWP* and CO2 and Methane

The first graph shows warming increasing as the emissions of both gases increase. In the case of carbon dioxide, it occurs at a much faster rate, simply because we’re creating an ever-larger stockpile of it over the Earth. Today’s emissions of carbon dioxide are being added to yesterday’s emissions and those of the day before, and the day before, and the day before, ad infinitum. It’s a different story for methane. Though warming increases when additional methane is emitted, it does so more slowly, because the methane of yesteryear is long gone, having been recycled.  

If emissions of the two respective gases remain constant, as shown in the second graph, warming from methane is flat. This is because methane is being destroyed at the same rate that it’s being emitted. Thus, there is no additional warming. On the other hand, carbon dioxide’s warming continues to increase, because it’s being added to the atmosphere without the earlier carbon dioxide being sequestered or destroyed.

Finally, in the third graph, emissions of both gases are drastically reduced. Carbon dioxide’s warming continues to rise and eventually levels off (but due to its long life span, remains in the atmosphere practically forever). Methane, on the other hand, creates a cooling effect. That’s owed to the fact that as methane is reduced, less carbon dioxide is produced from its decay. Plants continue to need carbon dioxide, and they will naturally draw from the surplus of carbon dioxide from other activities if methane isn’t providing enough. While we grapple with how to reduce our national and even global footprint, methane can help keep global warming at bay, providing we succeed in reducing it.

GWP* and methane from cattle

California Dairy Digesters
Dairy digesters on a California Dairy. Photo courtesy of Dairy Cares.

I’m hopeful that we can, at least where livestock is concerned, reduce its warming impact and even turn it into cooling. GWP* can better inform our progress and help us get there. In the United States, methane emissions from livestock have decreased over the last half century as herd sizes have steadily gone down while output has gone up markedly. Consider that California’s dairy herd peaked in 2008 and has since declined by 7 percent, meaning since then, California dairies have contributed cooling to the climate. Meanwhile, animal-agriculture scientists are working diligently to develop feed that results in lower methane emissions, to name but one example of how science and technology can help us add more cooling.

Still, atmospheric concentration of methane has increased since the early 2000s, largely due to fossil fuel production, according to new research. It goes without saying that we need to find and embrace renewable energy sources and reduce waste.

A word of warning in regard to methane and the climate

While methane mitigation could alleviate the problem of global warming and actually lead to cooling effects, it would be short-lived relief if we don’t decrease carbon dioxide emissions. Since carbon dioxide is a stock gas, continuing to accumulate and further warm the atmosphere, the stockpiling of carbon dioxide will eventually overcome the benefit brought about by a reduction in methane. We need to aggressively reduce our carbon dioxide emissions by focusing on our reliance on fossil fuels, the biggest contributor by far to global warming. Other initiatives – such as planting trees – simply fall short by orders of magnitude of getting us to where we need to be.

Nevertheless, reducing methane is a significant short-term opportunity that we should pursue. California dairies have reduced methane emissions by 25 percent using technologies such as manure digesters, positioning the state more than halfway to meeting its 2030 goal of reducing methane by 40 percent. They also have reduced their carbon dioxide emissions by incorporating solar energy, LED lighting and electrification of feed-mixing and water-pumping operations. It is an accomplishment that benefited from farmers, regulators and researchers working together to solve a problem. We need more of that as we move forward.

Don’t take it personally

I don’t want to suggest that personal choices don’t matter. We all need to be conscious of and respectful to each other and to our planet. Still, if we ever hope to change the global warming trajectory, it’s critical that we understand the facts and come together to find real and lasting solutions. Eating meat and dairy products is not the problem. In fact, it might well be part of the solution.   

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