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Hey, CO2!  What Have You Done for Me Lately?
Volume 4, Number 28: 11 July 2001

From its pre-industrial level of 150 years ago (approximately 275 ppm), the air's CO2 concentration has risen to nearly 375 ppm today.  What has this extra 100 ppm of CO2 done for world agriculture?

Mayeux et al. (1997) analyzed this question with respect to wheat, which they studied in a 38-meter-long controlled environment chamber located in a ventilated glass house.  This chamber was composed of five 7.6-m lengths of a 0.76-m-deep and 0.45-m-wide soil container topped with a transparent and tunnel-shaped polyethylene cover that was attached to its upper edges.  Two day-neutral cultivars of spring wheat (Triticum aestivum L.) were grown in four 0.6-m-long soil compartments in each of the five 7.6-m-long sections of the tunnel.  In addition, a third spring wheat cultivar was seeded into the middle and two ends of each tunnel section prior to the planting of the two cultivars to be studied, i.e., Seri M82 (a semidwarf type representative of modern spring wheats) and Yaqui 54 (a traditional tall cultivar typical of what was used by American farmers 40 years ago).  The third wheat cultivar served as a photosynthetic "sink" for CO2 as air passed through the chamber sections, so that a CO2 gradient was created through the "long and winding tunnel," from near 350 ppm at its entrance to approximately 200 ppm at its end.

Both of the studied wheat cultivars were irrigated weekly over the first half of the
100-day growing season, so as to maintain soil water contents near field capacity in each of the chamber sections.  Over the last half of the growing season, however, this regimen was maintained on only half of the wheat of each cultivar, the other halves receiving no further additions of water in order to create droughted treatments in addition to the well-watered treatments.

At the conclusion of the experiment, the scientists determined that the growth response of the wheat was a linear function of atmospheric CO2 concentration in both cultivars under both soil water regimes.  Based on the four linear regression equations they developed for grain yield in these situations, we calculate that the 100-ppm increase in atmospheric CO2 concentration experienced over the past century and a half should have increased the mean grain yield of these two wheat cultivars by approximately 72% under well-watered conditions and by about 48% under the water-stressed scenario the scientists studied, for a mean cultivar/water scenario response on the order of 60%.

This CO2-induced increase in commercial wheat productivity is considerably larger than what is generally observed in studies that elevate the air's CO2 concentration to values above where it currently stands, due to the fact that the aerial fertilization effect of carbon dioxide is expressed much more strongly at lower atmospheric CO2 concentrations than it is at higher concentrations.  Hence, there has been a tendency for the past benefits of the historical increase in the air's CO2 content to be significantly underestimated, based on analyses of forward yield projections derived from atmospheric CO2 enrichment experiments.  As the backward yield projections derived from the results of the atmospheric CO2 depletion experiments of Mayeux et al. clearly indicate, however, the historical rise in the air's CO2 content has already increased real-world wheat yields by an astounding amount.

But the good "old" news is not restricted to wheat.  Based on the voluminous data summarized by Idso and Idso (2000) for the world's major food crops, the calculations we have made for wheat can be comparatively scaled to determine what the past 150-year increase in atmospheric CO2 concentration has likely done for other agricultural staples.  Doing so, we find that the Industrial Revolution's flooding of the air with CO2 has resulted in mean yield increases of 70% for other C3 cereals, 28% for C4 cereals, 33% for fruits and melons, 62% for legumes, 67% for root and tuber crops, and 51% for vegetables.

So the next time you hear someone spouting off about the evils of fossil fuels and the CO2 they emit to the atmosphere, tell them the other side of the story.  Tell them they might not even be here without what the burning of coal, gas and oil has done for the planet in providing a goodly portion of the food that has sustained our enormous population growth of the past 150 years.  Yes, there's more than just blood flowing through our veins; there's a bit of fossil fuel coursing through them as well.

Dr. Craig D. Idso
President
Dr. Keith E. Idso
Vice President

References
Idso, C.D. and Idso, K.E.  2000.  Forecasting world food supplies: The impact of the rising atmospheric CO2 concentration.  Technology 7S: 33-55.

Mayeux, H.S., Johnson, H.B., Polley, H.W. and Malone, S.R.  1997.  Yield of wheat across a subambient carbon dioxide gradient.  Global Change Biology 3: 269-278.