The California judge in the climate change liability trial wants to know if human respiration is a problem for climate change. Humans are breathing out carbon dioxide (CO2), and human population has increased dramatically in just the past century. Is this part of the climate problem? (I wrote about this previously but am now revisiting it.)
Here’s the question that the judge asked:
“In grade school, many of us were taught that humans exhale CO2 but plants absorb CO2 and return oxygen to the air (keeping the carbon for fiber). Is this still valid? If so, why hasn’t plant life turned the higher levels of CO2 back into oxygen? Given the increase in human population on Earth (four billion), is human respiration a contributing factor to the buildup of CO2?”
Well, yes, the grade school analysis IS still correct. Further, given the increase in human population, human respiration IS a contributing factor to the buildup of CO2. But it is not nearly as significant as livestock respiration. The biomass of large animals — mostly livestock — has dramatically increased, to levels not seen in the past 100,000 years or so. Livestock biomass far exceeds that of humans and wild animals combined. And the reason why plant life hasn’t “turned the higher levels of CO2 back into oxygen” is that humans and livestock are devastating plant life on earth. Plant phytomass has declined by about half in the last 2000 years and by about 17% just in the 20th century.
Unfortunately, this is not the answer that some otherwise well-informed climate scientists are giving. The Real Climate site gives this answer (as of March 16):
“The carbon in the exhaled CO2 comes from the food that the animals have eaten, which comes (ultimately) from carbon that plants have taken from the atmosphere during photosynthesis. So respiration is basically carbon neutral (it releases CO2 to the atmosphere that came from the atmosphere very recently).”
This answer is similar, though not identical, to explanations I have seen other respected people making. Al Gore (who presumably is being well advised by some scientists) simply says vaguely that “we get carbon from plants, breathe it out, and they take it in again.” Doug Boucher puts forward a similar argument, saying that “the CO2 that plants take out of the atmosphere, goes back into the atmosphere [through decomposition by microorganisms], whether or not they are eaten by animals.”
All of these explanations fail in approximately the same way. They do not compare the rate of photosynthesis and the rate of respiration. Respiration MAY be carbon-neutral, if the rate at which animals (and microorganisms) exhale CO2 is balanced by the rate at which plants take up CO2. Boucher’s, Gore’s, and Real Climate’s explanations seem to want to say that by definition respiration and photosynthesis will be matched. Whether they are actually matched, though, is an empirical, scientific question, not a question of logic or definitions. The fact that these three answers are all slightly different but that none of them address the question of balance, suggests that these climate scientists have not really thought through this whole issue.
A key part of the carbon cycle is on display here: plants take up CO2, animals give it off. If animals are exhaling CO2 faster than plants are taking it up, then CO2 will start to build up in the atmosphere, resulting in global warming. (It’s also possible that plants would take up CO2 faster than the animals could exhale it, in which case CO2 levels would fall and we would have global cooling.)
We need to be investigating whether this part of the carbon cycle is out of balance. We have dramatically increased the number of cows (and people) during the past 500 years. All of these cows will all consume plant matter and “[release] CO2 to the atmosphere that came from the atmosphere very recently,” but if we keep adding cows, the rate at which CO2 is put back into the atmosphere will go up. To be in balance, we would need to see a corresponding increase in the rate at which CO2 is taken out of the atmosphere by plants.
Common sense would suggest, though, that a different result is entirely possible. As more and more cows are added, we might see a decline in plant matter — a consequence, perhaps, of soil erosion, overgrazing, and cutting down the rainforest to create pasture land. And that is exactly what we observe during the past few centuries: animal life increasing, plant matter decreasing.
The central issue is whether this respiration-photosynthesis process is in balance, so that respiration is balanced by an equal amount of photosynthesis. Will the extra CO2 from billions of extra people and extra cows be taken up by plants? Well, maybe, unless we’ve destroyed the plants. Given the evidence of mass destruction of the natural world, the burden of proof should be on those who say that respiration is “carbon neutral,” not on those who are saying that the cycle is currently tipped against photosynthesis. Tipping this cycle against photosynthesis is what we are doing right now with livestock agriculture.
The climate change liability trial itself is quite interesting. Several cities in California are suing the oil companies over climate change. The judge asked eight questions; the respiration question is number 6 in the list. The judge wants both sides to prepare a tutorial on climate change addressing these questions.
I worry that the positions you take in this & previous blogs on the same subject are, in some ways, mistaken or unsubstantiated to an extent that basically weaken the case for causes that we share.
First let me be clear that I am “on your side”. I rarely buy books these days (due to my financial situation and the amount of material available on the Web). Most of the books I have recently purchased (though admittedly second-hand) have been of your writings. I find what you have written on Christianity exciting, largely persuasive and fitting well with my own preconceptions. Also I have been a non-ovo vegetarian for more that 50 years and non-ovo, non-lacto vegetarian for more than a decade. From that stance it is easy for me to come to the conclusion that current livestock practices are ecological and ethical disasters.
Your thesis is that the stock of carbon dioxide in the atmosphere is in some significant degree being increased by a flow from livestock respiration beyond the flow: photosynthesis => plant growth => animal metabolism. But for this to happen there has to be a reduction of carbon in some stock (other than atmosphere) somewhere and where that would be is not obvious. And the process of getting that carbon into the animals must also be identified.
To be a little more concrete, if animals were being fed from a fungus that lived off carbon stocks in the soil, then we might see an increase in carbon dioxide in the air that did not come “immediately” through photosynthesis. Then we would see a decrease in the stock of carbon in the soil. Such a decrease is happening but it seems unlikely that it is through livestock ingestion.
Admittedly I tend toward abstract analysis such as that of stocks and flows so consider a simple, concrete model of ecological disequilibrium from human and livestock impact.
Whether true or not, there are tales of sailing ships leaving goats on isolated islands so that in the future, mariners in distress might find food there. The goats would then eat up everything available and die off. This might seem to be a case of respiration exceeding photosynthesis within the isolated island system but we’d be a lot more concerned with other effects than an increase in atmospheric carbon dioxide. In the goat case, the carbon stock being drawn down is the extent vegetation on the island. I invite proponents of the animal respiration hypothesis to imagine factors added to this simple model that would illustrate their point.
My counter hypothesis to the one you propose is that if there was an excess of carbon dioxide being put into to the air by livestock (over the amount returned by photosynthesis) that drew directly on the carbon stock of extent vegetation to the degree that you posit it would show up in characteristic livestock feeding practices and ecological dislocation in a way that would be glaringly detectable. Remember is requires amount of carbon and path of transmission.
As far as I can tell, the data that would address the issue are simply not at hand. Important factors in the carbon cycle are still being uncovered such as the magnitude of changes in ocean photosynthesis, permafrost thawing, methane release, etc. We don’t know what’s happening with the bacteria and in the oceans. The livestock industry is not eager to see its ecological balance sheet examined.
You understand the situation exactly. That’s why I try to emphasize that respiration occurs simultaneously with photosynthesis. If there’s too much of one, there must be not enough of another. Or, it could affect other parts of the carbon cycle, e. g. you could have increased absorption of the CO2 by the ocean, or something else.
In this case the carbon stock which is declining is easy to identify. It is the total plant matter on the planet. Plants incorporate carbon into themselves via photosynthesis. Vaclav Smil (see link in the body of the blog, at the point where I state “Plant phytomass has declined . . .”) estimates that plant matter has declined by roughly half in the last 2000 years, and by 17% just in the 20th century. In fact William Ruddiman (in Plows, Plagues, and Petroleum) estimates that human destruction of the environment (mostly agriculture) resulted in an elevation of about 40 ppm of CO2 during the period from the beginning of agriculture to 1700, before the industrial age and the massive burning of fossil fuels.
You’ve also nailed another critical point. It may be that the most serious consequence of this is not global warming (assuming that we dodge a runaway global warming scenario somehow), but that we run out of plants to eat. That’s why soil erosion is such a big concern for me, even though it’s not nearly the issue that climate change is in the public’s mind. Soil is formed naturally, but the process takes place over centuries whereas we are eroding over a period of years. We’re burning through the earth’s soils and right now the main way this has come to our attention is that the climate is a bit warmer because carbon is entering the atmosphere.
I would turn the question around, and ask, what would it look like to see this tremendous increase in animal respiration, and NOT see a rise in CO2 levels? There are several ways this could happen. The main way would be for there to be a huge increase in plant growth. The plants could utilize this extra CO2 to ramp up their growth and extract this extra CO2 from the air. This point is often made by climate denialists who say that “CO2 is plant food,” and as I recall there’s some evidence that this happens to a limited extent. This in fact seems to be the judge’s question as well, and the oil companies might try this argument in court.
However, this seems not to be happening. In fact, the reverse is happening. Another more prosaic way for CO2 levels NOT to rise, would be for the oceans (or the soil, or something else) to absorb CO2, and to a certain extent this is happening also. Because the carbon cycle is so huge — vastly more carbon is cycled through the system every year than is emitted by fossil fuels — the exact consequences of disrupting this or that part of the cycle is hard to predict, and this is hard to explain to the public. The consequences of injecting extra CO2 into the atmosphere from outside of the cycle completely, which is basically what is happening with burning fossil fuels, is also hard to predict. The evidence is strong though that the consequences are not going to be good and that very significant global warming is already one of them.
Don’t get me wrong; veganism is not enough, and we have to rapidly phase out burning fossil fuels as well. We have a lot to do, and most people do not understand the depth and gravity of the problem.
There is so much to say in so many of the points you bring up. I am restrained in my replies because I do not know how appropriate it is to go into matters at depth in this space. I wrote out some more which I will copy below and probably will continue to (as they say) “get into the weeds” until I get some indication that I should cut back. Before going on to specifics, some general clarifications. I find almost all the points you bring up to be absolutely central to our multiple dilemmas. I tend to not go into topics where I strongly agree with you. I am very concerned that, as best we can, we not claim more than we can strongly support. I believe we have the “truth” very much “on our side” and therefore need to be very scrupulous in our claims. Now, to one specific.
You write “The plants could utilize this extra CO2 to ramp up their growth and extract this extra CO2 from the air. This point is often made by climate denialists who say that “CO2 is plant food,” and as I recall there’s some evidence that this happens to a limited extent. … However, this seems not to be happening.”
It is (or was) happening. The extent to which it is happening seems to be detectably falling. The indication for this comes from the Keeling curve which tracks the growing amount of CO2 in the atmosphere. The curve is famous for its upward trend but looking at the curve one can notice also that it has a yearly cyclical component. This cyclical component is thought to be largely due to land based photosynthesis (and the fact that there is so much more land in the Northern Hemisphere). Analysis of this yearly summer recovery indicates we are loosing in the photosynthesis game. If there is sufficient interest I would be willing to track down some references to this. However, there are indications that ocean-based photosynthesis is in even more trouble. Also there is a very worrying potential for GMO based geoengineering with regard to photosynthesis.
Well I spent all too much time working on one approach (stocks & flows) before my memory & Google search reminded me of the short cut to the answer. The proportion of CO2 going into the air due to fossil fuel burning compared to “short term” plant+animal into air can be pinned down via carbon isotope ratios. The former (fossil fuel) is very, very poor in carbon 14 compared to the latter. That’s because carbon 14 is radio active and decays away drastically on geological time scales.
From there it depends on whether the researchers can be trusted. I’ve gotten to this point before all to often with deniers. You finally lay out how the researchers really can test for something and then they say “I don’t trust them!”
Here is a site that deals with the issue of carbon 14.
Can they be trusted? Well, first of all their data is not all that up-to-date but more importantly their statement, “Based on how much of the heavier CO2 they measure in samples of atmosphere, scientists calculate that about a quarter of the CO2 present today must come from fossil fuels” is rather misleading to the casual reader who is apt to say, “Hey that’s a lot!”, when what we want to know is the yearly figure, “What’s this year’s proportion?”
So going from the carbon 14 signature to answering the fossil fuel vs large herbivore respiration question is a good bit of work but maybe some people we could both accept as trustworthy have done that work. I suggest we throw out a challenge on the Real Climate website and see if can get a good answer.
I’ll put below some excerpts from the previous work I did on stocks and flows, namely the parts that don’t get into weeds on stocks and flows.
“ what would it look like to see this tremendous increase in animal respiration, and NOT see a rise in CO2 levels?” Less rotting, more eating. An even faster rise in ocean acidity than there would be if there was no increase in animal respiration.
You find the increase in animal respiration “tremendous” and yet the burning of fossil fuels isn’t so important because “the carbon cycle is so huge”. (“emitted by fossil fuels” = 1/“vastly more carbon”).
There are many different stock & flow models that can be applied to the same empirical data. What is a stock in one model might be a slow flow in another model. A good model does not leave things out and does not count things twice. That is not as simple as it sounds but …..
Conventional View: The amount of C used in photosynthesis devoted to grow the crops that end up being fed to large herbivores is very close (+ or -) to the amount of C expended in respiration & excretion, etc., by large herbivores. For significant amounts of extra C to be drawn from total carbon tied up in land plants (or soil), there needs to be a pathway from the plant material (or soil) into the herbivores. The extra carbon in the atmosphere can be well-accounted for by fossil fuel use.
A very sound model of stocks and flows needs to be used and it needs to filled out with “good” data.
What data do we have and how much can we trust it?
My own guess is that if a good model and good data were used, there would be a very large role for soil and ocean stocks, and the processes that connect them with atmosphere, plant & animal stocks.
This is quite interesting. I will have to study it further.
My intent in saying that animal respiration has increased greatly is that large animal biomass has increased, relative to the previously and historically existing scale of large animal biomass. This is the point of the graph from the Barnosky paper. The total amount of animal respiration, though, is much smaller than the total amount of CO2 put into the atmosphere (and taken out) by natural processes such as into and out of the oceans.
For what it’s worth, the Denver Post reports this morning (June 26) that the judge has now thrown out the lawsuits against the oil companies. Judge William Alsup said that the world has also benefited from oil and balancing the harms versus the benefits “demand the expertise of our environmental agencies, our diplomats, our Executive, and at least the Senate . . . The problem deserves a solution on a more vast scale than can be supplied by a district judge or jury in a public nuisance case.”