Scenario 1

The otherwise very useful web site “Skeptical Science” seems to be bent on minimizing estimates of the impacts of land use (and especially livestock agriculture) on climate change. They don’t think that animal or human respiration can possibly contribute to carbon dioxide (CO₂) emissions. Oh, really? To me it is fairly obvious that it could contribute to climate change, depending on how much we’ve destroyed the earth’s plant life that removes CO₂ through photosynthesis. But to “Skeptical Science,” it is equally obvious that cows and people can’t contribute to climate change by respiration. They become rather huffy when a number of people (in the comments section of this page) start to question their thesis. What is going on here?

In this blog I will propose a solution to this problem. “Skeptical Science” is talking about what I will call “direct land use emissions” of CO₂, but have failed to account for “indirect land use emissions.” Here is what “Skeptical Science” says. They publish the above graphic (which I am identifying as “Scenario 1”) with these statements:

“[The claim that breathing creates carbon dioxide emissions] fails to take into account the other half of the carbon cycle. . . . plants are the opposite to animals in this respect: Through photosynthesis, they take in carbon dioxide and release oxygen. . . . Therefore, when we breathe out, all the carbon dioxide we exhale has already been accounted for. We are simply returning to the air the same carbon that was there to begin with. Remember, it’s a carbon cycle, not a straight line — and a good thing, too!” (Emphasis in original)

Are the plants and animals in Scenario 1 in balance? Let’s accept, for the sake of argument, that this graphic represents a situation in which the carbon cycle is indeed in balance. The cow eats the grass, the cows and the human breathe out CO₂, the grass (or the tree) take it up through photosynthesis, and everything is in balance. Now let’s change this graphic:

Scenario 2

We’ve just put an extra cow into the picture. Thus the CO₂ emitted has increased. Now is it in balance? Well, maybe, depending how you interpret it; the graphic is becoming ambiguous. You could argue that photosynthesis must also increase and therefore that Scenario 2 is still in balance. Where is this extra cow going to get food? We have to assume that the human has, through agriculture, created some extra plants for the extra cow to eat — perhaps by growing some extra hay or growing some extra soy and corn for the cow. These additional plants, wherever they are, will add to the photosynthesis efforts of the plant world and balance out the respiration of the additional cow.

Scenario 3

Let’s be generous and assume that Scenario 2 is balance. What if we have a different, more extreme scenario, which is clearly unbalanced? How about Scenario 3, in which we’ve we’ve doubled the cows and tripled the people over Scenario 2? On top of that, we’ve chopped down the tree and burned it, symbolizing that the total quantity of plant matter is not even keeping up — it is actually decreasing. Now, is this in balance? No, clearly not. CO₂ is going to accumulate in the atmosphere.

Skeptical Science would doubtless agree that in Scenario 3 CO₂ has been added, but that it is already been accounted for as “land use change.” After all, land use change is an acceptable category of CO₂ emission, currently not thought to be very large.

“Land use change,” as used by “Skeptical Science” (and others), does not refer to the fact of imbalance between plants and animals. It refers to the one‑time extra CO₂ added to the atmosphere in the process of changing the use of the land. E. g., one year we burn down a forest, and the CO₂ from the burning wood is added to the atmosphere. In terms of Scenario 3, it’s the CO₂ released when that tree that’s been chopped down is burned. It incorporated carbon, now in the atmosphere as CO₂ — and that carbon has been accounted for. But what about next year, when no additional burning or deforestation takes place, but cows are turned loose in the area and the area remains with less vegetation? Haven’t we destabilized the area by introducing an imbalance, with fewer plants and more animals, and won’t this increase CO₂ as well?

We can now see the problem. There are two different phenomena here, and “Skeptical Science” is talking about only one of them.

(1) There are what I will call “direct land use emissions,” to which “Skeptical Science” is referring. Direct land use emissions have a specific point source. Burn down the Amazon rainforest, that’s certainly going to add CO₂ directly to the atmosphere through the burning of the wood which will form CO₂. (The EPA implies that “land use emissions” of CO₂ is only CO₂ put directly in the air from land use effects, e. g., burning trees.)

(2) But there will be another long‑term, chronic problem, the problem of “indirect land use emissions.” There are now fewer plants to metabolize CO₂ through photosynthesis, and more animals. This is an imbalance problem. It does not have a specific point source (like a cow or coal-fired power plant). There is no single cause that we can point to and say “that’s the cause, right there.” Because the imbalance problem persists from year to year, it is potentially much more serious than the problem of direct land-use emissions.

It’s easy to see why people might think that direct land use emissions constitute the whole story of land use emissions. The biosphere is a very big place. Human agriculture has greatly increased in productivity just in the 20^th century; we are growing a lot of extra plants. These extra plants must be photosynthesizing the extra CO₂ coming from the explosion of human and livestock populations.

Indeed, there must be plants somewhere that feed the extra humans and extra cows, but that the totality of plant matter has increased sufficiently to compensate for the extra CO₂ is an empirical claim, and probably false. Humans have done immense damage to the biosphere over the course of the last couple of millennia, with the destruction accelerating just in the 20^th century. During the past 2000 years, total plant phytomass has decreased by nearly half — and declined by 17% just in the 20th century. Indeed, the decrease may be even greater. In the meantime, while wild animals face extinction, total biomass of land megafauna (large animals) has increased over seven‑fold in the past 500 years. Most of this is our livestock, by the way, with 5% or less being all that is left of wild mammal megafauna.

It seems to be highly likely that in point of fact, we do have a serious imbalance problem due to the decrease in plant matter and the increase in humans and cows. This imbalance will lead to an indirect increase in CO₂ emissions. Eventually, this will also result in extinctions of all the wild animals that depend on this plant matter, and possible food shortages for humans.

In this light, it appears to me that land use — defined as the sum of both the direct and indirect land use emissions of CO₂ — is a key driver of climate change. We need to be trying to estimate its significance, rather than simply retreating into denial of the problem. None of this implies that direct CO₂ emissions from fossil fuels are any less of a problem than we previously thought. Quite the contrary. Rather, the sum total of land-use emissions is an additional source of net CO₂ emissions that we had not considered. The situation is much worse than we have been led to believe.