First and foremost, people must have sufficient food, simply to sustain themselves; and the rise in the atmosphere's CO2 concentration that has occurred since the inception of the Industrial Revolution (an increase of approximately 100 ppm) has done wonders for humanity in this regard.
In a revealing study of the beneficial impact of mankind's historical CO2 emissions on world food production, Mayeux et al. (1997) grew two cultivars of commercial wheat in a 38-meter-long soil container topped with a transparent tunnel-like polyethylene cover within which a CO2 gradient was created that varied from approximately 350 ppm at one end of the tunnel to about 200 ppm at the other end. Both of the wheat cultivars were irrigated weekly over the first half of the 100-day growing season, so as to maintain soil water contents near optimum conditions. Over the last half of the season, however, this regimen was maintained on only half of the wheat of each cultivar, in order to create both water-stressed and 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 adequate and less-than-adequate soil water regimes. Based on the linear regression equations they developed for grain yield in these situations, it can be calculated 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 the two wheat cultivars by about 72% under well-watered conditions and 48% under water-stressed conditions, for a mean yield increase on the order of 60% under the full range of moisture conditions likely to have existed throughout the entire real world.
It is also important to note that this CO2-induced yield enhancement was not restricted to wheat. Based on the voluminous amount of data summarized by Idso and Idso (2000) for the world's major food crops, the calculations made for wheat can be scaled to determine what the past 150-year increase in atmospheric CO2 concentration likely did for the productivity of other agricultural staples. Doing so, one finds that the Industrial Revolution's flooding of the air with CO2 resulted in mean yield increases on the order 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.