Thus, CO2 literally is the “food” that sustains essentially all plants (and animals who consume plants, including humans) on the face of the Earth. And when that food supply is diminished, nature begins to diminish.
In my last post I shared the results of research findings demonstrating that rising atmospheric CO2 levels represent no current direct threat to human health and/or cognitive performance and decision making. Further, I explained that they present no realistic future threat either; for CO2 levels would need to increase some 36 times above the present concentration before they would even begin to pose a mild health concern.
That value (i.e., 15,000 ppm) will never occur, given it is a factor of ten above the approximate 1500 ppm atmospheric CO2 limit that scientists think is possible if society utilized all of the currently-known fossil fuel reserves on the planet.
But what about low CO2 concentrations? Might they pose a threat to humanity? In short, yes. The lower the CO2 concentration, the greater the risk. This certainly applies to net reductions in PPM, but it also applies to reductions in CO2 from government climate policies against market preferences for mineral energies, natural gas, coal, and oil. The more CO2 the better, in other words.
Carbon dioxide is the building block of nature. It is the primary raw material utilized by plants during the process of photosynthesis to build and construct their tissues. Thus, CO2 literally is the “food” that sustains essentially all plants (and animals who consume plants, including humans) on the face of the Earth. And when that food supply is diminished, nature begins to diminish.
Consider, for example, the work of Faltein et al. (2020), who examined the impact of low levels of CO2 (relative to present, ambient CO2 air) on African wood-sorrel (Oxakis pes-caprae). O. pes-caprae was a key carbohydrate source for humans during the Middle Pleistocene, being regularly harvested by human gatherers for its edible underground storage organs (USOs).
Given that atmospheric CO2 is a substrate of photosynthesis and growth, Faltein et al. were curious to learn how much the bulb biomass of African wood-sorrel would have been reduced (relative to the present) in the Middle Pleistocene and how such a reduction would have impacted efforts to harvest sufficient biomass to attain daily calorific requirements.
To accomplish their design, the four South African researchers grew specimens of O. pes-caprae for three months in mini open-top-chambers under average CO2 concentrations of 227, 285, 320 and 390 ppm. All plants received sufficient water and nutrients. Not surprisingly, Faltein et al. report that at the end of the experiment plants grown under reduced concentrations of CO2 exhibited “significantly decreased plant biomass and bulb yield” (Fig. 1).
Figure 1. Bulb biomass of Oxalis pes-caprae plants grown under sub-ambient atmospheric CO2 concentrations for three weeks. The letters denote significant differences between treatments at P < 0.05. Adapted from Faltein et al. (2020).
For example, the scientists say that under the lowest CO2 levels, “bulb biomass decreased by up to 80% compared to current ambient concentrations, while total plant biomass showed a two-fold decrease.” Naturally, such growth reductions were attributed to “the fundamental effects of low [CO2].”
With respect to the human impact of such growth reductions caused by low CO2, Faltein et al. note that lower CO2 concentrations “affect both the value of USOs as sources of carbohydrates and the effort that would have been required to harvest sufficient biomass to attain daily calorific requirements.” And in regard to the latter, they calculate “the time required to harvest 2000 calories was more than doubled when [CO2] was decreased from 400 to 180 ppm.”
The above findings (and others discussed here) demonstrate that humanity benefits from higher levels of atmospheric CO2, which increase plant yields and enhance available carbohydrate supply. On the other hand, reducing the current CO2 concentration of the atmosphere, which has become a platform of far too many politicians and activists, has the opposite effect. And the greater the reduction in atmospheric CO2, the more devastating the impacts will be, as research indicates plants begin to die at CO2 concentrations lower than 120 or 130 ppm.
Consequently, any reduction in the CO2 content of the atmosphere will negatively impact the current state of nature, reducing not only the growth of plants, but other benefits brought about by higher CO2 concentrations, including greater water use efficiencies and the ability to better withstand environmental stresses such as drought, disease, high soil salinity, low light intensity, ozone pollution, heat waves, UV-B radiation, etc. Reducing these benefits would most certainly decrease global food supplies, potentially leading to civil unrest and conflict if the reduction is significant enough.
So, yes, there are consequences to reducing the air’s CO2 content by any amount. To claim otherwise or ignore this scientifically-based truth demonstrates the ignorance (and arrogance) of those hell-bent on reducing the CO2 concentration of the atmosphere.
Faltein, Z., Esler, K.J., Midgley, G.F. and Ripley, B.S. 2020. Atmospheric CO2 concentrations restrict the growth of Oxalis pes-caprae bulbs used by human inhabitants of the Paleo-Agulhas plain during the Pleistocene glacials. Quaternary Science Reviews 235: 105731.