This work revealed that the approximate 50% increase in the air's CO2 concentration employed in their several experiments reduced the Zn concentrations of the edible portions of the six crops they studied as follows: wheat (9.3%), rice (3.3%), field peas (6.8%), soybeans (5.1%), maize (5.2%) and sorghum (1.3%); and it also reduced the crops' Fe concentrations, in the same order, by 5.1%, 5.2%, 4.1%, 4.1% and 5.8%, although it actually increased the Fe concentration of sorghum by 1.6%.

Standing by themselves, these findings would pretty much support the 20 researchers' contention that "increasing CO2 threatens human nutrition," but not to any great degree. Furthermore, there is another side to this story that suggests just the opposite. And that is the well-established fact that atmospheric CO2 enrichment typically increases crop yields by even greater percentages, such that the total amounts of Zn and Fe made available to mankind by conventional agriculture is actually significantly increased by atmospheric CO2 enrichment.

To obtain some idea of the magnitude of this phenomenon, we turned to the Plant Growth Data section of our website, where we have tabulated the increases in numerous crop yields that have been documented in various CO2 enrichment experiments over the past couple of decades, which we have normalized to what would be expected for a 300-ppm increase in the atmosphere's CO2 concentration, while here we have reduced these percentage yield increases to what would be expected for the lesser CO2 enrichment of the air employed in the studies of Myers et al., obtaining the following downward-adjusted CO2-induced biomass increases: wheat (20.7%) based on 260 studies, rice (22.4%) based on 224 studies, field peas (18.1%) based on 29 studies, soybeans (28.2%) based on 190 studies, maize (15.9%) based on 27 studies, and sorghum (12.3%) based on 28 studies.

Clearly, the double-digit CO2-induced percent yield increases in the six studied crops far more than compensate for the single-digit CO2-induced nutrient decreases obtained by Myers et al. in their experiments. Yet when a reporter for the European Commission's Community Research and Development Information Service asked Myers about these yield increases, Myers merely said "there may be a little positive effect," when in reality this positive phenomenon more than overcomes whatever minor reductions in nutrient concentrations may be caused by increases in the air's CO2 content, to which Myers replied that "the people who work in this area would not want to hang their hat on that in the face of the many other negative effects of climate change, including heat waves, droughts and floods."

Here, again, Myers is wrong; for we are three of those people, and we do "hang our hats" on these demonstrable facts, whereas Myers feels the need to seek additional support for his stand on the matter; but he does so by merely mentioning "many other negative effects of climate change, including heat waves, droughts and floods." But here his approach is misguided on two additional counts. First, it presumes - without compelling real-world data to back it up - that atmospheric CO2 enrichment will indeed lead to "heat waves, droughts and floods," when this is mere speculation based on far-from-perfect climate models. And even if such things did occur, for whatever reason, Myers should know that (1) in CO2-enriched air, the optimum temperature for photosynthesis in most plants is generally higher than that which prevails at lower CO2 concentrations, as is the temperature at which heat-induced death occurs, which enables plants to better withstand potential negative effects of heat waves, and that (2) in high-CO2 air most plants also greatly increase their water use efficiency, which enables them to better withstand the negative effects of drought.

All things considered, therefore, it would appear that the ongoing rise in the air's CO2 content will enable mankind to produce much greater amounts of only slightly less nutritious food. And who of us is there that would rebel against eating just a couple more mouthfuls of the agricultural largesse provided by a truly CO2-enriched atmosphere?

Sherwood, Keith and Craig Idso

Reference
Myers, S.S., Zanobetti, A., Kloog, I., Huybers, P., Leakey, A.D.B., Bloom, A.J., Carlisle, E., Dietterich, L.H., Fitzgerald, G., Hasegawa, T., Holbrook, N.M., Nelson, R.L., Ottman, M.J., Raboy, V., Sakai, H., Sartor, K.A., Schwartz, J., Seneweera, S., Tausz, M. and Usui, Y. 2014. Increasing CO2 threatens human nutrition. Nature: 10.1038/nature13179.