Animal Agriculture and the Air We Breathe

By Andrea Alban-Davies

Although CO2 receives the most attention, it is actually one of the least damaging of all the greenhouse gases when it comes to health. Methane, on the other hand, is a precursor to ground-level ozone (smog) – itself a greenhouse gas –, which is a toxic air pollutant that can trigger serious respiratory problems.

The air in our atmosphere is a lot like the water in our oceans. We can consider its quality on a local level, but there’s no escaping that it’s a global issue. Just as water freely mixes across ocean basins, so gases remaining in the atmosphere become well mixed. While localized air quality and pollution problems can create respiratory and other health problems in one city and not another, the problem ultimately belongs to all of us. The global nature of our air is never more clear that when we talk about the atmospheric level of greenhouse gases, which is roughly the same all over the world, regardless of where emissions originate.

Most scientists agree that the main cause of the current global warming trend is human expansion of the greenhouse effect. The greenhouse effect itself – the warming that results when the atmosphere traps heat radiating from Earth back into space – is not a bad thing. In fact, without it, temperatures on Earth could not reach the life-supporting average of 59 degrees Fahrenheit. Water vapor is actually the most abundant greenhouse gas. The problem for us is that greenhouse gases come in two very different varieties: those that respond physically or chemically to changes in temperature or “feedbacks”, and those gases that are long-lived, remain semi-permanently in the atmosphere, and do not respond physically or chemically to changes in temperature, or “forcing” [climate change]. In the latter category is where we find carbon dioxide, methane, nitrous oxide, and fluorinated gases. And even within the category of “forcing” gases, we discover that not all are created equal when it comes to global warming potential (GWP) over a given period of time.

As most are well aware, our consumption of fossil fuels is responsible for a huge portion of the greenhouse gas emissions attributable to global human activities. What is less well understood is the role that our food choices make. There are many estimates on the greenhouse gas emissions attributable to livestock, each taking into consideration a number of different factors in their calculations. For the purpose of this article, I’ll use the widely accepted figure of 15% from the United Nations Food and Agricultural Organization. This figure doesn’t take into consideration all of the knock-on effects of raising livestock, but it does include some. Just to put it into perspective, that is more than the emissions attributable to the entire transportation sector.

How is it possible that livestock accounts for such a large portion of greenhouse gases? The full story behind this outsized impact is the type of greenhouse gases that the animal agriculture industry produces. Forty-four percent of livestock emissions are in the form of methane. The reason for this is enteric fermentation, or the digestion process, primarily of non-dairy cattle and dairy cows. Methane is produced as a by-product of the fermentation process, and is exhaled, belched, or expelled from these cattle. Methane is particularly potent when it comes to GWP; it is 25 to 35 times more effective at trapping heat when compared pound to pound with CO2 over a 100-year period. That’s why it’s possible for methane to comprise only 16% of greenhouse gases in the atmosphere, but to be responsible for anywhere from one-third to one-half of the current global warming trend. Fittingly, methane has been coined “carbon on steroids” by one prominent climate scientist.

Methane is a much more powerful greenhouse gas than CO2 because it absorbs more energy and breaks down much more rapidly. It has a half-life of approximately 8.5 years, compared with many decades for CO2. As such, the shorter the time span examined, the starker the disparity between the GWP of these two gases becomes. For example, if we look at the first five years instead of the first hundred, a ton of methane causes nearly 100 times the warming of a ton of CO2. To comprehend the magnitude of this difference, consider this calculation by climate scientists: a ton of methane emitted today will exert more annual warming than a ton of CO2 emitted today until 2075; not until the year <7300> will the cumulative warming exerted by the two become equal.

It’s not all bad news, though. The upside of the role that methane plays in global warming is that it’s a good target for emissions reductions. The very same characteristics that make methane so destructive – its shorter lifetime and its energy absorption capacity – also means that atmospheric levels are much more responsive to reduction by emissions cuts. Especially because global warming can accelerate dramatically due to feedback loops, it’s most important to focus on measures that can help keep the Earth from overheating in the short-term. That buys us breathing room to work on implementing expensive, longer-term measures to control CO2 emissions (which usually requires huge infrastructure and technology investments). Immediate reductions in methane emissions can translate into a substantial slowing in warming over the next few decades. Studies have shown that reducing short-lived gases like methane, and keeping them low is the way to have the biggest impact on warming over this century.

What’s the best thing that we can do to reduce our methane emissions (which also happens to be the cheapest and can be implemented immediately? Well, the statistics tell the story best, so here they are… According to the Institute on Climate and Planets at NASA, animal agriculture is responsible for approximately 30% of global methane emissions. This is close to half of man-made emissions. To put that into context, coal and oil mining/natural gas accounts for 20% of global emissions. The breakdown puts enteric fermentation at 16%, animal waste at 5%, biomass burning (largely burning jungle to graze cattle, or grow food to feed cattle) at 8%. Therefore, eliminating or, at the very least, massively downsizing animal agriculture would be a huge – and some would argue necessary – step to combatting global warming.

As an added benefit, cutting methane emissions would also have a considerable positive impact on human health. Although CO2 receives the most attention, it is actually one of the least damaging of all the greenhouse gases when it comes to health. In contrast, methane is a precursor to ground-level ozone (smog) – itself a greenhouse gas –, which is a toxic air pollutant that can trigger serious respiratory problems.

There’s also the remainder of livestock emissions to consider when making food choices. While methane is the largest single component of emissions, the remainder is made up of almost equal parts Nitrous Oxide (N2O, 29%) and CO2 (27%). I won’t go into the same detail on N2O (the third most influential greenhouse gas), but suffice to say that it has a GWP 265-298 times that of CO2 over a hundred-year period and can have deleterious effects on human health. I won’t delve into the non-greenhouse gases emissions attributable to animal agriculture operations, but there are a good number of them. The most well known is ammonia (which comes from livestock and poultry waste), partly because of its acrid smell. When it reacts with N2O, moisture, and other compounds, it creates nitric acid vapor and related particles, which, among its other harmful effects, often causes lung tissue damage in humans.

Eschewing animal products and choosing a plant-based diet is undoubtedly a hard step for most of us to take; and, sure, it means letting go of foods that many of us hold dear. But holding onto them comes at a cost that is worth examining.