I enjoy a good steak. I also enjoy lamb chops and pork ribs and many other kinds of meat. However, animal agriculture has been vilified over its contribution to climate change. Am I destroying the planet by eating meat?
Whether you instinctively respond yes or no to this question is driven in large part by your values and preferences. For example, here are two things about me: I grew up on a sheep farm and I like to ride my bike. This means I have a natural affinity for animal agriculture and I don't particularly care about cars. I'm definitely going to point at driving before meat eating if I'm asked who is the biggest climate-change villain. If I were a vegan race car driver, maybe it would be the other way around.
In this article, I try to strip out the value judgments. I calculate that I should feel about $0.42 of guilt per 8oz steak, or about the same as driving 21 miles.
Almost three quarters of global greenhouse gas (GHG) emissions stem from energy, most of which is from burning fossil fuels. Agriculture generates 18.4% of global GHG emissions, less than a third of which is from livestock and manure. Animal agriculture (5.8%) contributes less to global GHG emissions than transportation (16.2%), buildings (17.5%), or iron and steel production (7.2%), but more deforestation (2.2%).
Livestock emit relatively less GHGs in the US than in the rest of the world. In 2019, US livestock contributed 260.5 tons of CO2 equivalent emissions, which is 4% of the US total. Essentially all livestock GHG emissions are methane from burps and manure. Ruminant animals such as cattle, sheep and goats use their fore-stomachs to digest foods that humans cannot. In the fore-stomach, bacteria break down hard-to-digest food and emit methane as a by-product. Similarly, manure from livestock in feedlots or other confined facilities is often disposed of in lagoons where bacteria break it down and emit methane.
Crop cultivation contributes more GHG emissions than livestock, mostly nitrous oxide from nitrogen fertilizers.
Cattle generate almost all the methane emissions that come from burps (enteric fermentation). There are about 30 million beef cattle and 10 million dairy cattle in the US, so beef cattle emit three times as much methane from burps as dairy cattle. Sheep and goats are smaller than cattle and there are fewer of them, so their emissions are much lower. There are 5 million sheep and 2.5 million goats in the US.
Methane emissions from manure management are driven by livestock in confined facilities, which is why dairy cattle and hogs are the dominant producers of methane from manure. Beef cattle tend to live on feedlots only in their last few months of life, so they emit less methane through manure management.
So, how many pounds of methane would my steak generate? As I explained in a previous Ag Data News article, a typical 3-year old steer produces about 500lb of beef. It belches about 660lb of methane and emits another 66lb from its manure in its lifetime. So, my 8oz steak is responsible for 0.73lb of methane emissions.
According to this nifty calculator, that is equivalent to the 100-year warming effect of about 21 miles driving an average passenger vehicle, or 0.0083 metric tons of CO2. Using a social cost of carbon of $50/ton, the GHG cost of my steak is 42 cents.
Some caveats. This calculation excludes emissions from growing the corn to feed the cattle and emissions from meat processing. It also doesn't account for the reduced cropland emissions from using manure instead of synthetic fertilizer and the human food waste that was fed to cattle instead of dumped in landfills where it would have emitted methane.
Another caveat. Methane only lasts in the atmosphere for about 12 years, whereas CO2 lasts indefinitely. The warming effects of a single steak are really large in the first 20 years and much less in the following 80 years. So, if we want to prioritize slowing climate change now, then reducing meat consumption now is more important. However, if we care only about the temperature 100 years from now, then meat is a lower priority.
Global meat consumption is increasing as people get richer. If this growth continues, then meat will become a more salient contributor to climate change. The cheapest way to achieve large-scale mitigation of these effects will be new technology, just as it will in the electricity sector with wind and solar and in the transportation sector with electric vehicles. This means we should encourage large-scale investments into ways to reduce the amount of methane cattle emit, as well as alternative meats and lab meats. I may have an affinity for animal agriculture, but I also like new technology and new foods.
UPDATE: In an earlier version of this article, I listed cement manufacturing as contributing 3% of emissions based on the global pie chart. However, this accounts only for direct emissions from the chemical reaction that creates clinker. The energy used in cement production contributes another 3-4% of the global total.