How Do We Know Cows Are So Bad for the Climate?

How Do We Know Cows Are So Bad for the Climate?
Image: Benjamin Currie

The meat culture wars have shone a light on the uncomfortable truth: As delicious as they are, hamburgers aren’t so great for the planet. Agriculture makes up one-third of total methane emissions worldwide. While that encompasses a lot of different components, like land use and manure management, emissions from the cows themselves are a huge chunk of this problem: cows alone account for 27% of U.S. methane emissions.

Discussions around the harm methane in the atmosphere is doing to the planet have gained urgency in recent years, but scientists have actually known cows make methane for a long time. This basic agricultural science is now helping us better understand an increasingly thorny problem: How the natural process of cows creating methane is contributing to climate change — and what to do about it.

How Do We Know Methane Is a Problem?

Methane was discovered in 1776 by a scientist named Alessando Volta, who observed bubbles of methane in a swamp. The greenhouse gas was first documented in the atmosphere in 1948. But it wasn’t until NASA researchers figured out it was a greenhouse gas in the mid-1970s the interest really took off. That led scientists inspecting ice cores from Greenland and Antarctica for historical clues about our atmosphere to discover methane concentrations have more than doubled since the 1800s. Alarm bells have begun to ring even louder in recent years.

Earlier this month, the Intergovernmental Panel on Climate Change report marked a key societal marker of sorts for methane. The report noted atmospheric methane levels haven’t been this high in at least 800,000 years, and, for the first time, the group made it clear that there’s an urgent need to reduce methane emissions in order to stop the climate crisis.

“Methane is getting more attention now, as it should,” said Chris Field, a professor of environmental studies at Stanford University and the director of the Stanford Woods Institute for the Environment. “We are in a much more challenging situation with greenhouse gas emissions overall. I think in the past people would say well, carbon dioxide is the dominant gas, let’s focus on that and we’ll be in a position where we can have the conversation on methane down the road. I think because the impacts of climate change are so clear now, it makes sense to focus on greenhouse gases as well.”

How Do Cows Make Methane?

Cows are ruminants, a type of mammal that evolved to be able to digest grass using a special compartment in the stomach, known as the rumen. Grass is mostly cellulose, a tough type of carbohydrate that’s present in most leafy greens that people eat. But cellulose essentially comprises the entirety of grass, making it impossible for people to eat. Cows, however, have a bunch of tools in their bodies we’re not equipped with. When a cow chews and swallows grass, that grass enters into a multi-step process inside the cow involving four separate compartments in the animal’s stomach, intended to break down all that cellulose.

The rumen is the first step on this journey, and a pretty crucial one, acting as a fermenting pot for the cow to break down the grass.

“Food goes in rumen and churns around, and there’s no oxygen in there, but there are lots of microbes that help to break down the cellulose and ligaments and other long-chain carbs that we can’t digest,” said Alison Eagle, a senior scientist at the Environmental Defence Fund. “They break them down into something the cows get energy from.”

During the grass’s time being broken down in the rumen, some of those microbes create methane, which the cows then belch out — a process known as enteric fermentation. Cows also fart some methane, and lagoons created to store their manure can create methane as well, but it’s enteric fermentation that is the real conundrum in figuring out how to reduce emissions from livestock.

How Long Have We Known the Cow-Methane Connection?

“There’ve been many decades of study in the animal science departments at universities around the country where people said, ‘what’s the efficiency of cattle digestion?’” Field said. “We knew a lot about how cattle works and what the byproducts are, in order to help cattle with their diet and stuff, way before we cared about greenhouse gases.”

Because scientists and researchers were so interested in methane and the other byproducts of a cow’s digestive system, they’ve been recording estimates of methane emissions from cows for a pretty long time as well. The first figures estimating worldwide methane production from ruminants were published in 1949, while a separate study in 1970 separated out the estimated methane emissions from domestic animals specifically. In this case, climate science actually caught up to agriculture.

How Do We Measure Methane Emissions From Cows?

There are many ways to measure how much gas is coming from cows, ranging from studying individual cows all the way up to satellite-level view.

“You can put a gas mask on a cow,” Field said. “There are lots of experimental setups people use — sometimes you put a gas mask on a cow, sometimes they put the cow in a little box with airflow going in and out.”

He also noted that some people also look at air quality and emissions over feedlots. All those types of measurements are used to calculate much larger emissions levels from states or regions.

“It’s a big maths problem,” Eagle said, noting that doing so requires looking at bottom-up and top-down data to “make sure we’re in the same ballpark.”

If It’s a Natural Process, Why Is It Bad?

Enteric fermentation is a natural process, but we’ve added so many cows to the planet that it’s become a huge problem. In recent years, the dairy and beef industries have piloted a few techniques to reduce methane produced from cattle, including putting additives, like seaweed, in cow feed that help reduce the amount of methane produced.

“Feed people have been talking about methane management for decades,” Field said. “Some have promising results, but it’s really hard to get it to go to scale.” Adding seaweed also does nothing about the other kinds of emissions that come from raising cattle, like deforestation in the Amazon and manure ponds.

The beef and dairy industries have also claimed that more efficient feed has allowed them to efficiently produce more meat and milk per cow. That would theoretically slash methane emissions — if we kept the number of cows down, that is. Globally, demand for beef is expected to grow 88% between 2010 and 2050.

Experts agree that there are probably ways to seriously lower emissions without everyone giving up beef forever, but we definitely need to start thinking about a world with less beef.

“Maybe we should think about moderation, maybe we don’t need too many steaks,” Eagle, who stressed that EDF has no position on people’s dietary choices, said. “If we reduce methane now we will have some significant climate benefits that will be near term.”