Responding to the CO2 Coalition's "Facts #8 and #9" on US and Plant Growth with More CO2

CO2 Coalition's "Fact #8" and "Fact #9" want us to believe that more CO2 means more plant growth (Fact 8) and allow crops to feed more people globally (Fact 9). The claims here are not really new compared to other claims in this list of "facts," and we've already seen why these claims are misleading at best. We've seen in two posts (here and here) that increasing CO2 doesn't just cause greening through CO2 fertilization but also warming through the greenhouse effect. The latter increases heat stress for plants and limit their ability to make use of additional CO2 for photosynthesis. We've also seen here that CO2 Coalition just assumes that increases in corn yields are due to increased CO2 when the sources they cite actually attribute increases in crop yields to better hybrid corn and better technology. The logic of these facts is very similar. In "fact 9," we're shown a graph of grain production with CO2 and temperature, and we're left to assume that the CO2 is responsible for the increases in crop production. At no point is any attribution shown. And at no point to they consider the amount of crop production that would occur without increases in CO2 and temperature. That is, they don't even consider the possibility that CO2 and temperature are reducing crop yields with respect to a world without GHG-induced warming. Multiple studies (see below) show that crop production is already being reduced with respect to production expected without AGW.

And below they show a graph summarizing "270 laboratory studies (Idso, 2013) of 83 food crops showed that increasing CO2 concentrations by 300 ppm will increase plant growth by an average of 46% across all crops studied." But every single one of these are "laboratory studies," meaning that they are controlled experiments in which CO2 is increased and all other factors that could impact crop yields controlled for. These factors include temperature, water, pests, disease, and competition from other plants. All of these have a potential to limit crop production in the real world outside of greenhouses. We cannot feed the planet in greenhouses. We have to grow crops in open fields that are subject to temperature changes, droughts, floods, pests, disease, and weeds.

Numerous open air studies confirm that we simply cannot assume that greenhouse experiments will translate into increases in crop yields similar to those experienced in greenhouses. Here are a few examples:

1. Ziska 2000[1] showed that soybean yield increases under higher CO2 concentrations when grown in a weedless environment, but soybean yield decreases under higher CO2 levels when in the presence of weeds. The presence of weeds is compounded by the fact that some weeds are developing a resistance to pesticides like RoundUp.
2. Rumbidzai et al 2017[2] shows that increased CO2 can also benefit weeds, pests, and disease, which can outcompete crops and limit the response of crops to increased CO2.
3. Zhu et al 2018[3] shows that any increase in yield likely comes at the deficit of other nutrients, meaning that you'll need to eat more volume of crops to get the same amount of protein, vitamins and minerals. This makes sense to me because the benefit of more CO2 is basically just more photosynthesis, so it's going to be basically all carbs. 
4. Ortiz-Bobea et al 2021[4] has shown that climate change have already hurt farm productivity by about 21% since the 1961.
5. Lesk 2016[5] found that drought and extreme heat reduced crop yields by as much as 10% between 1964 and 2007.

CO2 Coalition is quite obviously cherry picking controlled lab experiments in greenhouses so that they can isolate benefits from CO2 fertilization and then hide from their readers the other challenges that plants (including our crops) can face as global warming continues.


References:

[1] Ziska, L.H. (2000), The impact of elevated CO2 on yield loss from a C3 and C4 weed in field-grown soybean. Global Change Biology, 6: 899-905. https://doi.org/10.1046/j.1365-2486.2000.00364.x

[2] Rumbidzai D. Katsaruware-Chapoto et al, "Responses of Insect Pests and Plant Diseases to Changing and Variable Climate: A Review." Journal of Agricultural Science Vol. 9, No. 12 (2017). https://www.ccsenet.org/journal/index.php/jas/article/view/66504

[3] Zhu et al (2018). Carbon dioxide (CO2) levels this century will alter the protein, micronutrients, and vitamin content of rice grains with potential health consequences for the poorest rice-dependent countries. Science Advances 23 May 2018: Vol. 4, no. 5, eaaq1012.
DOI: 10.1126/sciadv.aaq1012 https://doi.org/10.1126/sciadv.aaq1012

[4] Ortiz-Bobea, A., Ault, T.R., Carrillo, C.M. et al. Anthropogenic climate change has slowed global agricultural productivity growth. Nat. Clim. Chang. 11, 306–312 (2021). https://doi.org/10.1038/s41558-021-01000-1

[5] Lesk, C., Rowhani, P. & Ramankutty, N. Influence of extreme weather disasters on global crop production. Nature 529, 84–87 (2016). https://doi.org/10.1038/nature16467