2010-09-30 09:33:32Rebuttal #120: CO2 is plant food (UPDATE: removed until I work on it some more)
John Cook


This argument was written by John Russell. Unfortunately John asked me to take on finishing off this rebuttal as he has had to restrict his computer time due to an eye condition (hope you're getting better, John).

Have temporarily taken this down - sorry for the confusion. Shouldn't have posted this until I'd had time to work with it more.

2010-09-30 09:43:43In my opinion


this is Advanced.

It's worth doing up properly, but then someone needs to streamline it considerably to reach Intermediate.

2010-09-30 09:48:44Sorry, streamlining it as you're reading it :-(
John Cook

I think advanced could go even deeper - will post within a day or two on my plans for how to approach the advanced rebuttals. This just needs some massaging, which I'm doing now.
2010-10-01 06:43:55


I think it's intermediate because it gives a lot of details but using a conversational style. Maybe it's too long, but I enjoyed the reading.

2010-10-01 06:59:54Length is an issue


An article that requires sustained attention for a long time is going to be hard to read. This fact needs to be taken into account.

I have ranted and raved about limiting the reading level (and I will continue to do that); but another issue that has been investigated is that in the age of the internet, we don't have the attention span we used to. We've become accustomed to operating in an environment of near-constant distraction, by email, by cellphones, by pop-ups, whatever - and especially when looking at a screen. We don't have the patience to read to the end of a long article to get the point. 

If you have in mind an Advanced version that is even longer than this, I suggest splitting it into two parts. 

But I still think this is too long for Intermediate.

2010-10-08 07:28:27
Shirley Pulawski

I think links to the plant nutrient charts would be enough - they take up a lot of room on the page, and I don't think they really help the argument. Also, I don't understand the connection with this aprt:

It’s worth knowing that Abutilon theophrasti, introduced in the 1700s, is an invasive species in some agricultural regions of the US causing decreases of up to 34% of corn yield if not controlled.

This example indicates the incredibly complex unintended consequences of a change in atmospheric CO2 concentration can produce.


I don't understand what CO2 has to do with corn or invasive species??? If it's about unintended consequences, I'd leave it out. It is long. It's also informative, but there are probably some paragraphs that could be reduced without losing their message or dumbing-down.


2010-11-13 18:23:15
Glenn Tamblyn



Just some general comments about subject areas that might be useful for inclusion in this - Basic, Intermediate or Advanced. These are just snippets I have heard here and there.

How much of the yield improvements observed in Greenhouse studies is attributable to adding CO2 to counter CO2 depletion in greenhouses.

What do the various FACE (Free Air CO2 Enriched - I think) studies around the world tell us?

What is the impact of CO2 on protein content as distinct from total biomass. How does this differ between planst with the C3 & C4 photosynthesis pathway.

How else do plants respond to CO2. Paleoclimatologists use stomata counts on fossil leaves to estimate ancient CO2 levels. With more CO2, do plants need fewer stomata to satisfy their CO2 needs. Since Stomata are also used for thermal regulation, how does reduced stomata numbers impact on their capacity for thermal regulation.

With easier access to CO2, can plants devote more resources to things like self-defense. What happens to self-defense toxin levels in plants in a CO2 enriched environment. I saw a program suggesting something like this in Cassava Plants a while back.

What are the intersections between CO2 levels and Temp rise. Does the temp rise from CO2 have a greater impact on plants than the impact of the CO2 alone. Lester Brown from the Earth Policy Institute suggested something like this in an article in SciAm a year or so ago. 1DegC reduces yields by 10%. This might be tracked back to the International Rice Research Institute, I'm not sure.

My take on the impact of CO2 & Temps on plants is that it is more likely to be bad than good for us and the ecosystem. However, the effect will be complex with some benefits. The point of a rebuttal of this argument is less that it will be all bad - we can't justify that. But rather that the simple statement that more CO2 is good for plants is wrong BECAUSE it is simplistic.

This sceptic argument is one to be negated, but it can't be turned into a strong pro AGW position apart from the precautionary principle which is hard to argue strongly to a general audience.  The best we can really say about this is its more likely to be bad than good, but we can't be sure. But bad on this front means really bad. Food Supply!