"Earthman"

Cows and Carbon for Dummies

Published 6 months ago - 8 Comments

It is popular to claim that cattle are bad for the environment, and the best thing we can do for the planet is to eat a plant-based diet.

So let’s look at the carbon cycle, specifically as it applies to grazing cattle, and try to see how cows can be a net GHG emitter. I’m not going to throw out statistics and numbers (which can easily be manipulated), but instead apply a little basic science and a big slice of good ol’ common sense.

How does carbon move in the cow’s lifecycle? Here are the main transactions.

  • Grass takes carbon dioxide from the air (and a little carbon from the soil)
  • Cows eat the grass
  • Cows release carbon back onto the pasture through manure (and a bit through urine)
  • Cows inhale air and combine some of the oxygen with carbon to create CO2, which is then exhaled
  • Microbial activity in the cow’s digestive system creates CO2 and methane, most of which is burped out (some exhaled and farted)
  • Carbon may be harvested by calves, humans, or other animals in the form of milk and/or meat.

Level 1: Practically All Carbon Comes from the Air

The first, and most important, thing to notice is that the way the vast majority of carbon enters this cycle is through photosynthesis. Grasses draw carbon out of the air to build the above-ground edible grass and the matching root system below ground. The same is true if cattle are fed on tree forage or crop residues. (They may draw a little carbon from stuff going on in the soil, but hey, that carbon originally came from the air too.)

So any carbon that is emitted back into the air from the cow originally came from the air. That fact alone almost closes the case. If all the carbon in the cycle comes from the air, and some of that carbon goes back into the land, then – if we’re measuring carbon atoms alone – grazing cattle must be net storers of carbon, not emitters.

ALL the carbon came out of the atmosphere originally, so it’s impossible to add more than was taken out.

In fact, it’s obvious that cattle must remove more carbon from the air than they put back because they can also provide poop, milk, and meat (in fact, every part of the animal).

So… if grazing cattle actually remove carbon from the atmosphere and help build soil, how can we best accelerate that process?

Level 2: Accelerating Carbon Removal

Perennial grasses can have massive root systems

When grass grows, it creates a root network in the soil that is approximately the same depth as the height of the grass above ground. (It is a waste of energy to build more roots than the growing plant needs.)

So when the grass is grazed, the plant actually sloughs off some of its root system, which remains underground and decomposes, adding carbon to the soil.

Plants also engage in a complex series of trades with other organisms to get the nutrients and minerals they need. Key to this are mycorrhizal fungi, specialised fungi that have adapted to exist symbiotically with plants, and also with bacteria that coat the mycorrhizal strands.

The plants “pay” the mycorrhizae by exuding organic sugars (which contain carbon), for which the fungi trade nutrients from the soil. In turn, the strands themselves also exude glomalin, a sticky glycoprotein, which helps to glue soil particles together, giving soil its structure and facilitating air and water to circulate through the soil. Glomalin also contains a substantial amount of carbon.

Now, grass left alone without grazing will reach its full height, and then basically stop growing until it dies or is destroyed, at which point it will be broken down and reabsorbed into the soil and air. Full-grown grass doesn’t need to photosynthesise as much, so doesn’t cycle as much carbon as it was in its busy growth phase.

But what happens when grass that is eaten? Provided it is not grazed right down to the ground, which slows down growth dramatically, grasses will put a lot of energy into regrowing rapidly. That means they’ll initially release unneeded root mass, and then rebuild root mass and above-ground leaves. The middle half of a grass’s growth curve (between 25% and 75% fully grown) is the most active. The more active the grass, the more CO2 it’s sucking out of the air and storing both below- and above-ground.

So letting cattle graze (but not over-graze or under-graze) actually accelerates CO2 storage (known as “sequestration”) in the soil.

The most effective grasses are the perennial grass species, which have much deeper, more massive, root systems than annual grasses that may be used in a short-term rotation. So permanent pasture is much more effective at storing carbon than the shorter, annual grasses.

The frequency of grazing is also a critical factor. Ranchers really want their cattle to arrive on grass that is approaching its full height (so it is still growing, and not going woody or going to seed), but they don’t want the cattle to graze the grass right down to the ground. In other words, they want the cattle to have one or two bites and then to move on.

The way to do this is by rotating the cattle frequently, moving them from plot to plot on a regular basis (the frequency depends on a wide range of factors).

Summary: The way grazing is managed can make a huge impact on the amount of carbon drawn down from the atmosphere and stored in the soil.

“Ah, but what about Methane?”

Some will argue, “Okay, so cattle can’t actually add more carbon into the air, but if they change its form into methane (which everybody knows is a far more potent greenhouse gas than CO2) that could be worse.”

It’s a fair argument. Methane is approximately 30 times more potent at driving atmospheric warming than CO2.

I think the easiest way to address the methane argument is by using good old-fashioned common sense again.

Before we came along and took over management, this planet must logically have supported more large grazing animals than it does now. Why? Because that’s the way nature works. Every ecosystem would have supported as many grazers as it could, based on available resources. And, before man started farming, all viable grazing land would of course have been grazed.

So, if large ruminants like cattle, sheep, deer, and goats were net polluters in greenhouse gas terms, the world would have choked on methane long ago. It didn’t, therefore ruminants must not be the problem.

We can see this by looking at historical atmospheric methane levels, thanks to https://www.methanelevels.org/. Below are the records from the last millennium.

Previously, the levels over the past 800,000 years seem to have fluctuated regularly between 400-800 PPB (parts per billion). Click on the top-left icon to see the levels going further back.

Clearly, methane levels (which we can measure pretty accurately by analysing ice cores) were historically more or less stable up until the mid-18th Century, and have since skyrocketed to near 2000 PPB.

Why? Clearly it isn’t because we have more grazing animals, because we don’t. It is most likely due to human activity, primarily fossil fuel extraction.

So I would conclude that anyone with an ounce of common sense can see that grazing cows cannot be destroying the environment!

That is not to say that the clearing and burning of rainforests and the growing of huge areas of crops to transport to feedlots for cattle are not disastrous. They surely are both damaging and unethical.

But that is a problem of mismanagement, trying to find ways to slash costs and maximise profits, which inevitably leads to mining our world’s natural resources, instead of looking for sustainable or regenerative methods of feeding ourselves.

Conclusion

“It’s not the cow, it’s the how.”

8 comments