Cows and Global Warming

by Brian Dunning
January 28, 2025

Years ago when I first heard that cows burping and farting was a major contributor to global warming, I wasn't sure if it was satire or real. I had to admit it sounded more like a joke than science — here were the far-out hippie liberal extremists really scraping the bottom of the barrel to frighten us into becoming vegans — or something. And honestly, it wasn't really high on my radar for a long time while I was writing about other aspects of warming, mainly things like the proof that all the incremental warming of the last couple hundred years is human caused, proofs like spectroscopic analysis of our atmosphere layers to prove that the excess heat is being trapped by CO₂, and like isotopic analysis of that carbon proving that it came from the burning of fossil fuels and from nowhere else. So eventually, staying on the path of science brought me back around to cow farts — because why not.

One of the biggest stories in the intersection of agriculture and warming research is the issue of deforestation. Most notably, huge chunks of Brazil have been deforested in order to create grazing land for livestock, mostly beef cattle. It's not exactly new earth-shaking news that all that rain forest is a big carbon sink, and the more of it you take away, the smaller the carbon cycle's total capacity becomes; and the more excess CO₂ has nowhere to be absorbed so it stays in the atmosphere. That deforestation is where I expected an analysis of the livestock industry's role in warming would lead me. And while that's true, it turns out it's a drop in the bucket. It turns out that livestock actually do play a much larger role in warming, and possibly one that may be surprising to many. The supervillain here is not CO₂, but methane.

Let's recall Skeptoid #797, "Why You Need to Care About Methane." The cause of global warming is greenhouse gases. It's not all just CO₂, although that's the bulk of it. CO₂ is the biggest problem because its half-life is about 100 years. Once you put it into the atmosphere, it stays there trapping heat for a long time. However, the rate of warming, which is really high right now, is driven more by methane. Methane is not as big of a long-term problem because its half life is only about 9 years. But the reason it's the biggest driver of the warming rate is that it traps more heat than CO₂. A lot more heat. Over 20 years, a given amount of methane traps 84 times as much heat as the same amount of CO₂. So curbing CO₂ emissions is essential to minimize long-term warming, and curbing methane emissions is the best way we can slow the rate of warming.

And of all the methane our planet pumps into the atmosphere — some 600 Mt (megatons) a year — about 60% of it is human caused. So a whole lot of the immediate problem truly is in our hands to address. 60% sounds like a lot, but we also have an ally in chemistry. Our atmosphere contains molecules called hydroxyl radicals, which react with methane and convert it into water and CO₂. About 45% of it turns to water; about 55% turns to CO₂. Our atmosphere can do this to 550 Mt of methane a year, so if you take away the human contribution, it would be a big net loss. The fact that just over half that broken down methane remains in the atmosphere as CO₂ makes this an even more urgent task.

So the question becomes one of where we can make the most reductions. So let's start by breaking down the sources of the human-caused methane contribution:

Obviously those first two are the big ones. The production and use of fossil fuels contributes about 110 Mt, and livestock farming contributes about 100 Mt — almost as much as the fossil fuel industry.

So next we'll drill down deeper, and see where all those livestock emissions are coming from. This one's pretty simple. About three quarters of it are the burps and farts we've all heard about. This is called enteric fermentation. Ruminants — which include cattle, sheep, and goats — have a large single stomach divided into four compartments, the first and largest of which is called the rumen. They eat fibrous plant material, which is difficult to digest. They will repeatedly regurgitate some of it from the rumen back up to the mouth to chew on it some more — this is a cow "chewing its cud". Inside that rumen is a wild community of bacteria, protozoa, and fungi specialized to break down the cellulose and other plant material until it's ready to move on to the other stomach compartments. This chemical process is called methanogenesis. Most of it happens right there in the rumen, close to the mouth, so the majority of the methane is exhaled as burps. Only a small part makes it all the way through the digestive tract to come out as farts. Burps and farts all considered, the average cow produces about 300 liters of methane a day. That's a lot of methane.

Just that right there comprises three quarters of the methane from worldwide livestock farming. The other quarter is nearly all from manure management. All that manure has to get bulldozed somewhere, where it's stored, treated, converted into fertilizer, or otherwise disposed of. Methanogenesis continues throughout all those processes as the manure continues to break down.

Although 100 Mt seems like an incredible amount just for our industry livestock, plenty of studies have been done confirming this. Some of these published studies have pretty entertaining photos — big plastic collection bags attached to both ends of a cow, or cows in these little pressure chambers happily chewing away while scientists with labcoats and clipboards take notes through the glass. But the interesting thing about this particular 100 Mt is that this amount alone makes the difference between net methane being added, which is what's happening now, versus net methane going down every year as a result of the natural atmospheric reactions. So how can we push this down far enough to get below that threshold?

There are two basic ways it can be done. First is employing economic levers to change behavior. We tax behavior that we want to discourage, and we incentivize behavior that we want to discourage. This makes it more profitable for people to make choices that benefit everyone. In this case, it would mean a meat tax or dairy tax, to incentivize people to make different diet choices. A lot of countries around the world already have this, or are pondering it. Among them is Denmark, but its approach is a new one: rather than taxing consumers, they're taxing the farmers: 300 kr for each ton of methane they produce, beginning in 2030. Revenues resulting from such meat or dairy taxes are typically given back to livestock producers in the form of incentives to use production methods that reduce methane emissions.

The second option is to engineer our way out of the problem. This is something that a great deal of effort has already been expended on, and the various solutions are really interesting. One is to use selective breeding to favor livestock that naturally produce less methane. Another is to genetically engineer gut microbes that will consume the cellulose and produce less methane in doing so, and will outcompete the other microbes already in the gut. All of these are being done.

Another method is food additives, some of which are already on the market, others of which are coming soon. One is Bovaer, widely used around the world, which contains an enzyme inhibitor and can reduce methane emissions by up to 30%. Another is Rumin8, a new product composed largely of compounds from seaweed, with potential to reduce emissions by up to 80%. An obvious problem with food additives is the cost, since they have to be given at every meal.

So a less expensive option is a vaccine, such as one being developed by ArkeaBio, which only needs to be administered once every few months. This would stimulate the cattle to produce antibodies that would target methanogens, and could reduce emissions by some 20%.

There is a third basic strategy of course: Encourage everyone to become a vegan. I'm not even going to talk about this, because it's a complete non-starter. Everything we know from the entire history of economics shows that any solution that depends on people changing their behavior to make less favorable choices, with no benefit to themselves, is a fool's errand. I know many listeners out there are saying "Hey I did it, why can't everyone follow my example?" We know from history that they won't, not without economic levers.

Also bearing a mention are the meat alternative products, such as plant-based meat products already widely available, and even lab-grown meat products that aren't yet available. These products face a very big uphill battle from the populist culture wars. Industry leaders Impossible Foods and Beyond Meat are losing market share and value alarmingly, and some competitors, like vegan chicken nugget producer Nowadays, have had to close their doors. It's to the point that Impossible Foods changed the color of their packaging from green to red in a bid to appeal to meat eaters. But regardless of their market pressures, these alternatives depend on consumers choosing to make the switch, and too many people like meat; so, as economic theory tells us, it's not going to happen without leverage.

So in summary, yes, taking animal products out of your diet, particularly meat and dairy, is one thing that every individual can do to incrementally move the needle to slow warming. It's just not a very big one. It would be if everyone did it, but of course that's not going to happen. Really the most impactful thing that everyone can do is still at the ballot box: vote for politicians who understand basic science and don't ignore it, and who will work to shift our energy systems to carbon-free sources. Vote for carbon taxes. Vote for methane taxes. Learn about and support these new ways that scientists and farmers can reduce methane emissions at the source. And the one thing that everyone can always do: always be skeptical.

By Brian Dunning
Follow @BrianDunning