What do you think of the oversimplified myth 'CO2 is plant food'?

Hah thanks for the question. I wouldn't say I tore it apart though so much as tried to qualify it. It doesn't make sense to me how some people can argue that the climate is far too complex to predict, then turn around and try to present complicated topics like plant responses to CO2 in extremely simplistic terms. Maybe they just aren't aware of all of the variables that exist, so hopefully articles like this can bring them to light.

I'd like to point out that david b helped out a good deal with this, by explaining some of the trickier concepts to me and providing some great references.

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EDIT: Eric, thanks for reading it.

<<In other words what he just said is that co2 is plant food but certain studies shows that the benefits are not as great as skeptics say.>>

That's correct. As I said though the purpose of the article was mainly to emphasize that it is a complex topic. The main reason for mentioning the smaller yield increase of FACE studies was to show that the very frequently used "greenhouse owners use more CO2" analogy is an oversimplification. FACE studies prove that you can't just translate results from greenhouse studies to the real outdoor environment.

<<Finally, these open air studies are flawed because while you may be able to control the amount of co2, you cannot control the amount of precipitation, temperature and sunlight. Three factors that are very important to plant growth. Maybe Dawei can clarify this last point for me.>>

I agree that this is a problem, but I don't think it makes them "flawed". It's a common trade off seen throughout the natural sciences: the more closely your experiment matches the natural setting, the more you tend to have to sacrifice some control over the variables. A study in an isolated growth chamber may know all of the most important variables with great accuracy, but it would just be "flawed" in the opposite extreme, in that it is no longer close to what a plant experiences in the real world.

One solution might be to try to piece together studies of both types and get an overall picture. But despite the fact that this would be a truly monumental task, I don't believe the sum of all research that's been done can provide enough data to even begin to try it. In the meantime hopefully better technology will allow for improved measurements of these variables without interfering with the realism of the experiment.

Life expands to the limits of the resources available.

It is constrained by scarcity of resources. If a plant's growth is constrained by the amount co2 available then providing more will allow it to develop further. Growth will expand untill either that CO2 again becomes the limiting resource, or another resource becomes the limiting factor.

Carbon is a fairly scarce resource for a plant; it can't simply absorb it through it's roots, it has to convert it from CO2 in the air. Providing additional CO2 will usually remove access to carbon as the limiting constaint on growth.

Whilst providing additional CO2 might not help plants of "a certain species in a certain region", as a general rule it will... untill another constraint is met.

It IS this simple.

Since when did photosynthesis have flavour?

Re "The global increase of CO2 is thus a grand biological experiment, with countless complications that make the net effect of this increase very difficult to predict with any appreciable level of detail."

If there is more CO2 available than the plant needs, it will simply not photosynthetise it. That's not complicated.

I wouldn't go as far as saying it's a myth. ~45% of plant dry matter is carbon, the only source of carbon for plants is atmospheric CO2. As Dawei points out quite articulately there is a defined benefit at the biochemical level in C3 plants (which is the most abundant photosynthesis pathway) to increased CO2 concentrations.

-however-

Using the argument that CO2 is plant food is a pathetic (at best) justification for inaction against anthropogenic emissions of CO2. As has been pointed out, plant growth is dependent on many factors (so many in fact that designing reliable experiments that fully capture the nuance of environment interactions is next to impossible). Assuming a 1:1 relationship between atmospheric CO2 and plant growth will never come true. If plants were capable of fully capitalizing on increases in atmospheric CO2 then we wouldn't have a steady global increase in CO2.

In the end I think Dawei did a phenomenal and even handed job at addressing the issue, it is a complex and nuanced subject and thus far the results are far from conclusive despite the fact that several very strong trends have emerged.

We are conducting a very grand experiment with the globe. Several large scale changes to the physical and biological systems of the planet are coming down the pipe. Some of these changes may be beneficial at local scales (and maybe even larger) and others may be detrimental. The fact of the matter is that biological systems are complex and intertwined and *all* life 100% depends on the primary production that occurs in the process of photosynthesis. Increased CO2 may benefit plant growth, but potential changes in the myriad other environmental variables that plants need for growth may quickly eclipse any benefit realized.

Things are working pretty well right now. Why go screwing around with a system we barely even understand.

@Eric C - most FACE studies can control for irrigation if needed. However the natural environment of the FACE system is always coupled with a control treatment. In comparing control versus increased CO2 most other environmental variables are unimportant as they are both treated exactly the same except for CO2 concentrations.

I think the same thing about that oversimplified argument as I do of the CO2 is a pollutant argument.

Overall it is clear that adding CO2 to the atmosphere, is likely to slightly help plant growth, but cause other problems and that the problems would be worse than the benefit. Still do not, however, accept the runaway, world is going to end, scare-mongering predictions of those who would pretend to want to reduce CO2, yet not even consider nuclear power.

Aslo, while you pretend as if the CO2 is plant food, is a myth and that the skeptics have been torn apart as liars, reading Dawie's article, it seems very clear that the warmers were not lying, and did base their statements on scientific studies. Furhter, given the nature of more "real-life" solutions, having less ability to control for other factors, that these results suggest less benefit, but certianly do not suggest no benefit.

In other words, you act like you have shown the warmers are nothing but liars who refuse to undderstand science, when the truth is that they based their argument on real scientific studies, that other studies sugget that they are still right, though not to the same extent.

Sort of like saying I can beat anyone in basketball, including Shaq, as long as I define beating him at basketball, as really meaning that I can beat him should he become paralyzed.

EDIT:

Overall you are still left with a quandry. One of the major basis for the fear of AGW has to do with our ability to feed ourselves. Now given how quickly farming equipment can be moved and farming buildings set up, the question becomes: Given all AGW predictions are true, will the overall cummulative impact of all changes with:

Positive:

More farmland in high elevations and farther north

Slightly better plant growth with CO2 increase (note slightly better as per Dawei's argument as opposed to much better as per the skeptic argument.

Negative:

Loss of land to desertification

Loss of land to ocean

In order to make the claims that the warmers have made in terms of food, they would have to show that the negatives far outweigh the positives, which I do not think they have convincingly done. This is all under the large assumption that their predictions are right. AS for the plant food arguemtn, I think the only reason people are getting away with calling CO2 a pollutant with the general populous, is because the general populous, do not understand the difference between CO2 and CO as Eric C stated. Further, you should be aware that the warmers are making an argument for action based upon ability to feed ourselves. The plant food argument is not an argument for inaction, but simply a retort of your reason for action based upon production of crops.

The Mr. Blob approach works if you are dealing with solutions to problem where the solution is known to be far less costly than the problem. With the solutions that have been proposed and the uncertainty in the entire CC field, this is hardly the case.

Dawei wrote a very nice post, putting a lot of information into a small area. I had read of many/most of the papers mentioned by Dawei at various times. It is good to have all this info gathered in one place, and easily accessible because well-written. Congratulations Dawei! Nice job. Thanks. If anything, I'd like to see an expansion of the article.

CO2 IS "plant food." There is a global carbon balance, with photosynthetic fixation, aerobic and anaerobic digestion, fossilization, and combustion of annual biomass and fossil carbon. The major reservoirs of carbon are CO2 in the atmosphere, CO2 dissolved in the sea, carbonate rock, standing biomass, and fossil carbon.

Atmospheric CO2 functions as a thermal blanket for the earth. Lacking such a blanket, the Moon is frozen, at the same distance from the sun, while the coarse earth average temperature is closer to 50 degrees. Variations with latitude and altitude allow formation and retention of substantial land ice, but the bulk of water on earth is now in the liquid rather than solid state.

In the Permian, 400 million years ago or so, there was no land ice,. Atmospheric CO2 was three times the present concentration. There were vast shallow seas with lush forests on their shores. Large quantities of vegetation fell into the water and were entombed in sediment, eventually converted to coal as the layers of sediment above them built up and pressed down. The trapped carbon had been withdrawn from the atmosphere - after a while, the resonant heating effect was weakened enough for ice ages to occur.

Fixation rates of carbon have been too low to compensate for increased release due to combustion for at least a century or two. CO2 content is doubled, although still less than Permian concentrations. The effect of civilization is to lower net fixation of carbon into plant mass while raising net release through burning.

It is a question of logistics whether a dedicated biomass production effort can compensate for the burning of coal. You have to grow several tons of wood for every ton of coal burned, in the same amount of time.

It does not seem possible.

If a manager doesn't like an idea for some reason, or doesn't like you, or doesn't understand the argument, or is just an indecisive dufus, they can kill a project by what-if-ing it to death. But what about this? What about that? Have you factored in every possible scenario? What if... OH FOR CHRIST SAKE SHUT UP! ARE WE GONNA DO THIS THING OR NOT!

It's plain as day that whole bunches of things are necessary at some concentration and are toxic at other concentrations. Some CO2 is actually required for animal respiration. At slightly higher concentrations it's toxic. Same thing with the atmosphere. But no, that's not good enough. You need to prove it scientifically to five nines or your whole argument is bogus. Oh please. Not that we don't need to prove things to five nines. But that at some point well before that we know enough to understand what is going on.

I think this myth and other pointless distractions are analogous to the oversimplified thought processes in the average denier brain.

Very nice summary by Dawei. Unfortunately, five nines of logic can't overcome one nine of dufus.

Dawei is arguably the most brilliant and knowledgeable commenter in Yahoo Answers global warming, and that is not just damning with faint praise, but I am quite underwhelmed by this piece. It will be too long and technical for most lay people (what is C3 and C4?) who rely on skepticalscience, and the science in it tends towards the theoretical. It has stylistic flaws too, including typos, and rubbed me the wrong way off the bat by opening with the frankly stupid media line that I am sick of hearing: "In the climate change debate". There is NO SINGLE "debate" - that is a denier myth. There are many legitimate mini-debates on aspects of science and policy and one mangled tangle of a deliberately foggy faux-debate between 2+2=4 and 2+2 doesn't = 4, or we don't know, or arithmetic is a hoax.

I will say that there is a good survey here of many scientific aspects of what is called -in the one great line reminding the reader that it is the witty Dawei writing here - "a grand biological experiment." But this is really not necessary. The basic science question is simply stated: Is the biosphere a viable long term net carbon sink or not? The answer to that will depend on what happens across hundreds of ecosystems, and how well measurements can track it, not on how well each little aspect of the complex science of carbon in plants shakes out. The policy aspect is even simpler: CO2 is BOTH plant food and a greenhouse gas capable of inducing serious and, for humans, overall negative, long term climate change. The whole hue and cry about "plant food" amounts to just another confirmation of the degree to which juvenile delinquency is at the root of denial of climate change science. It would be laughable if nearly half the populace of the worlds' top economy were bamboozled into thinking things such as "water is essential to life, therefore lifeguards are creeping socialism."

I already thought the myth was a complete load of bovine leavings.

But that paper does pretty well put a spike in any notion that it's anywhere near as simple as "Plants need CO2, so more CO2 is good for plants"

Possibly a bit too technical for the uneducated/nonbiologists, however, could maybe use a "basic" version that explains the biology involved in simpler terms.

CO2 is not a significant variable (or rarely) in regards to plant locations.

Temperatures, topography, aspect, soils, rainfall etc etc are all considerably more significant in determining plant species distribution and health.

Considering climate change is occurring (anthropogenically influenced or not) the key thing to remember is that a change in temperature and rainfall will have considerable more influence on plants than CO2 levels.

Also it is important to remember that CO2 is absorbed quickest by fast growing young plants. Old trees store more carbon bu absorb less CO2 (as growth slows ... similar to how humans need more food when more active).