How much does agricultural activity contribute to greenhouse gas emissions? It’s an important question, but one whose answer varies depending on the source. In the U.S., for example, the Environmental Protection Agency has calculated that 5.8 percent of total gross anthropogenic (man-made) emissions of carbon dioxide (CO2) are associated with the agricultural sector. But that is just one greenhouse gas (GHG) in one nation. Estimates for the total contribution of GHG from all agricultural activities on the planet can reach as high as 51 percent. But is that possible?
A review of the leading scientific literature on the subject suggests that the 51 percent figure is overblown. Instead, analyses by the World Resources Institute (WRI) and the UN Food and Agricultural Organization (UN FAO) place the estimate between 14 and 18 percent of all anthropogenic GHG emissions.
That’s significantly less than half of global GHG emissions, yet even the lowest estimate (14 percent) is still neck and neck with WRI’s estimated emissions for the transportation sector (13.5 percent). So the question then becomes, why does agriculture emit so much GHG?
It’s Mostly the Livestock
First, a quick refresher on global warming and greenhouse gases.
The main contributor to global warming is carbon dioxide. While CO2 nourishes plants and is good for soil, too much of it in the atmosphere is bad for the planet as a whole. CO2 absorbs the thermal energy of the sun and does not dissipate for a very long time, trapping heat very much like a greenhouse does (hence, “greenhouse gas effect”). But CO2 is not the only greenhouse gas to worry about. The next two most common GHG are methane (CH4) and nitrous oxide (N2O). Together, these gases plus CO2 make up about 99 percent of all GHG in the atmosphere.
While the majority of global warming activities give off carbon dioxide, the agricultural sector primarily emits CH4 and N2O. Livestock such as cattle produce methane as part of their digestion cycle. In fact, the CH4 produced from “enteric fermentation” (i.e., cows farting) represents almost one-third of the emissions from the U.S. agricultural sector, according to the EPA.
Cows are different from pigs and chickens in this regard, as the latter animals do not produce methane. Cows are also significantly more costly to feed and more damaging to the environment. One 2014 study estimates that producing beef requires 28 times more land, six times more fertilizer and 11 times more water than producing pork or chicken. As Skeptical Science explains, this means that “producing beef releases four times more greenhouse gases than a calorie-equivalent amount of pork, and five times as much as an equivalent amount of poultry [emphasis added].”
This explains why a very vocal segment of environmentalists insist that eating red meat is bad for the environment and encourage consumers to go vegan. And while it is true that eating too much red meat is bad for your health and a vegan diet is likely the healthiest option (click the links to learn more on these topics), the breakdown of global GHG emissions shows that this claim, too, is somewhat overblown. However, as more developing countries acquire a taste for red meat, cattle production is expected to increase and, with it, GHG emissions.
That’s why cutting down on red meat is not the crackpot notion it is frequently painted to be.
Agriculture’s GHG emissions do not come from cattle alone. Various methods of irrigation, tillage and soil management lead to the production of N2O, and the use of manure contributes to both CH4 and N2O emissions. Clearing space for agriculture (e.g., deforestation) is also a contributor to carbon emissions and land degradation.
And as the World Future Council points out, soil erosion caused by agriculture and natural processes is also a significant cause for ecological concern. Though not directly related to global warming, its impact will be felt more acutely as the climate changes and the amount of top soil is reduced worldwide.
So What to Do?
Agriculture is arguably the most essential sector of the global economy, but there is something you can do to reduce its GHG emissions at the individual level. As mentioned above, cutting your intake of red meat is a good place to start. Eating more vegetables is a good next step. Again, to quote Skeptical Science:
“Eating vegetables produces lower greenhouse gas emissions… For example, potatoes, rice, and broccoli produce approximately 3–5 times lower emissions than an equivalent mass of poultry and pork (Environmental Working Group 2011). The reason is simple – it’s more efficient to grow a crop and eat it than to grow a crop, feed it to an animal as it builds up muscle mass, then eat the animal.”
The most important thing to remember is that global warming is a global problem, and improvements are needed in every sector of the economy. Agriculture is not the only emitter of CO2, N2O and CH4, and there are plenty of ways to reduce your global footprint in your daily life. If we all do what we can to use less, recycle more and pursue energy efficient or even net-zero policies, then we can all still have a steak once in a while.