Volume 10, Number 25: 20 June 2007
Much has been written of late about the legal technicalities associated with the attempts of climate alarmists and other radical environmentalists to brand carbon dioxide or CO2 an atmospheric pollutant, primarily for the purpose of regulating (actually, restricting) anthropogenic CO2 emissions. Perhaps the best way of determining if CO2 truly merits this designation is to perform a simple experiment to see what effects its partial removal from the air would have on something of great value to life on earth, such as a common food plant like the cucumber. Fortuitously, the results of just such an experiment were recently reported in the scientific literature; and it is to them that we turn for a resolution of this important issue.
Noting that greenhouses in northern countries are often not ventilated during autumn, winter and spring, Klaring et al. (2007) report that "in nearly airtight energy-saving greenhouses, this may result in CO2 concentrations dropping to very low levels due to the CO2 uptake by plants," which leads us to wonder: What effect does this reduction in greenhouse-air CO2 content have on the growth of greenhouse-raised cucumbers?
In an attempt to answer this question, the four researchers developed a system to maintain the CO2 concentration of the air within a greenhouse at the same concentration as that of the air outside the greenhouse. This they did by adding CO2 to the air of one of two identical greenhouses at approximately the same rate at which it was being removed by the photosynthetic activity of the cucumber plants it contained (and at approximately the same time), as estimated by two simple photosynthesis models.
Based on our visual inspection of Klaring et al.'s graphs of hourly atmospheric CO2 concentrations within a greenhouse treated in this manner and within another greenhouse where the CO2 removed by the photosynthesizing cucumber plants was not replenished, we calculate that over the daylight periods of two separate experiments they conducted, there was a mean daytime reduction of approximately 110 ppm (from approximately 395 ppm to about 285 ppm) in the greenhouse-air CO2 concentration caused by the growth of the plants in the non-CO2-replenished greenhouse. And this reduction in the air's CO2 concentration, according to what they report, led to a 28% decrease in cucumber fruit yield, which is the same percentage by which the greenhouse air's CO2 concentration was reduced by the photosynthesizing cucumber plants in the control or non-CO2-replenished greenhouse.
Now the partial removal of an atmospheric pollutant from the air would be expected to have a positive impact on important plant processes; but in the case of the perceptive cucumbers (which could not be fooled), just the opposite was observed: letting the cucumbers partially remove from the air what some people want to call a pollutant (CO2) and not replacing it actually harmed the cucumbers, by significantly reducing their productivity. Thinking of this experiment in reverse leads to the same conclusion: the 38% increase in the CO2-replenished greenhouse air's CO2 concentration significantly boosted cucumber fruit yield (by a similar 38%), which is not what an air pollutant does, but what an aerial fertilizer does.
Clearly, you don't have to consult a Supreme Court Justice to learn that CO2 is not an air pollutant. Just ask a cucumber.
Sherwood, Keith and Craig Idso
Reference
Klaring, H.-P., Hauschild, C., Heissner, A. and Bar-Yosef, B. 2007. Model-based control of CO2 concentration in greenhouses at ambient levels increases cucumber yield. Agricultural and Forest Meteorology 143: 208-216.