Often you will hear idiotic climate change deniers such as Rupert Murdoch saying that carbon dioxide is ‘good for plants’. Of course, this is based on their limited school-level knowledge of plant physiology. At that level of understanding, plants ‘inhale’ carbon dioxide and ‘exhale’ oxygen. This is basically true, but it is a much more involved process than that. In plant photosynthesis, the energy of light is used to drive the oxidation of water (H2O), producing oxygen gas (O2), hydrogen ions (H+), and electrons. Most of the removed electrons and hydrogen ions ultimately are transferred to carbon dioxide (CO2), which produces organic compounds, such as carbohydrates (e.g., starch and sugar). Other electrons and hydrogen ions are used to reduce nitrate and sulphate to chemical groups used to construct amino acids, which are the building blocks of proteins.
In their simple-minded conception of the world, climate change deniers seem to believe that more carbon dioxide in the atmosphere means more growth for plants and therefore more food for humans. However, as you would expect, science has demolished this drivel.
A recent study by people at Stanford and Rice universities in which they tried to predict ecosystem responses given the likely changes in climate and atmospheric composition. Among approaches for predicting ecosystem responses, long-term observations and experiments can be powerful approaches for resolving single-factor and interactive effects on measurements of net primary production (NPP; i.e., plant growth). They undertook a 17-year study of California grassland exposed to warming, added precipitation, elevated carbon dioxide and nitrogen deposition. The single-factor and interactive effects were not time-dependent, which allowed them to analyse each year as a separate experiment and extract NPP as a continuous function of the various global-change factors. They found that when temperature and precipitation increase, when carbon dioxide and nitrogen are at ambient levels, NPP increased. However, when nitrogen was added NPP went up, and when carbon dioxide was added NPP increased, but only at lower temperatures. So, more carbon dioxide at higher temperatures will decrease NPP4,5.
On top of this, there has been another study by people from the US and Ireland on the physiology of plants with an increased level of carbon dioxide. Plant and human tissues (e.g., leaves, retina) both have a need for carotenoids to protect them against light-induced and other oxidative stresses. While plants synthesise carotenoids themselves, humans must obtain them primarily through consuming plant-based foods. In plants, elevated levels of atmospheric carbon dioxide have been shown to decrease the concentrations of essential minerals, including magnesium and zinc (essential for brain and eye health), but the overall effect of globally rising carbon dioxide levels on carotenoids has previously been unknown. This investigation is a meta-analysis (an analysis of other studies) examining how carbon dioxide affects carotenoids in plants. It used 1026 experimental observations from 37 studies and showed that carbon dioxide decreases plant carotenoid concentrations by an average of 15% (range: 26% to 6%). This raises a novel question about the potential effects of rising carbon dioxide on human health through its global effect on plant carotenoids6,7.
People like Murdoch seem to think that if they believe something strongly enough then it must be true, their complete ignorance of the topic at hand notwithstanding. It is a common problem among narcissists and the religious. However, if you want to find out what is true about the natural world, we have to resort to science, and not fairy stories from idiots.
- Zhu, K., Chiariello, N.R., Tobeck, T., Fukami, T. & Field, C.B., 2016. Nonlinear, interacting reponses to climate limit grassland production under global change. Proceedings of the National Academy of Sciences 113 (38), 10589-10594.
- Loladze, I., Nolan, J.M., Ziska, L.H. & Knobbe, A.R., 2019. Rising Atmospheric CO2 Lowers Concentrations of Plant Carotenoids Essential to Human Health: A Meta-Analysis. Molecular Nutrition and Food Research 63 (15), 9 p.