On the CO2 Fertilization Effect (real science for EPA)

By Robert Bradley Jr. -- August 11, 2025

“What would happen if CO2 doubled from the current approximately 400 ppm in the atmosphere to 800 ppm? Crop yields worldwide would increase by about 40%, based on empirical findings of how CO2 concentrations affect crop yields.” (Lindzen and Happer, below)

“Greenhouse Gases and Fossil Fuels Climate Science” by Richard Lindzen (MIT) and William Happer (Princeton University) contains many arguments against climate alarmism and thus the U.S. Environmental Protection Agency’s 2009 Endangerment Finding, now subject to reversal. This particular section of the recent Lindzen/Happer study (April 2025) concerns real science, CO2 science, versus non-testable, causality-errant climate models. This testimony in regard to the repeal of the CO2 endangerment finding will be important.

Lindzen/Happer’s general conclusion is (p. 43): “The common belief that CO2 is the main driver of climate change and the EPA Endangerment Finding assertion that ‘elevated concentrations of greenhouse gases in the atmosphere may reasonably be anticipated’ to endanger the public health and welfare are scientifically false.” A key argument concerns the undeniable benefits of CO2, stated as follows.

Increasing CO2 in the atmosphere increases the amount of food that plants produce, a phenomenon called “fertilization.” Thousands of experimental results demonstrate that more CO2 usually increases the amount of food that plants produce.⁴⁶ A graphic illustration of the response of plants to increases in CO2 is shown below. Dr. Sherwood Idso grew Eldarica (Afghan) pine trees with increasing amounts of CO2 in experiments, starting with an ambient CO2 concentration of 385 ppm. He showed what happens when CO2 is increased from 385 ppm to 535 ppm, 685 ppm and 835 ppm over 10 years: ⁴⁷ (Page 18)

The “fertilization” effect varies significantly by type of plant. Dr. Craig Idso reported, “[s]ince the start of the Industrial Revolution, it can be calculated … that the 120-ppm increase in atmospheric CO2 concentration increased agricultural production per unit land area” for various crops ranging from 28% to 70%, and averaging 46%.⁴⁸ He also reported “CO2–induced activity productivity increase[d]” one of the varieties of rice by 263%,⁴⁹ and that a 300 ppm increase in CO2 resulted in an average increase of 46%.⁵⁰

What would happen if CO2 doubled from the current approximately 400 ppm in the atmosphere to 800 ppm? Crop yields worldwide would increase by about 40%, based on empirical findings of how CO2 concentrations affect crop yields.51

What if the Net Zero Theory went into effect now and CO2 does not double to 800 ppm? There would be 40% less food worldwide. Thus, more CO2 means more food for people worldwide. Reducing CO2 to Net Zero means less food for people worldwide, but with only a negligible effect on temperature.

Sylvan Wittwer, the father of agricultural research on this topic, eloquently emphasized the enormous benefits of providing more food to people worldwide by rising CO2:

“The rising level of atmospheric CO2 could be the one global natural resource that is progressively increasing food production and total biological output … The effects know no boundaries, and both developing and developed countries are, and will be, sharing equally.”52

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46 See, e.g., NIPCC, Climate Change Reconsidered II: Biological Impacts (2014); Craig Idso, “What Rising CO2 Means For Global Food Security” CO2 Coalition (2019); Plant Growth Database, Center for the Study of Carbon Dioxide and Global Change.
47 Craig Idso, Increased Plant Productivity: The First Key Benefit of Atmospheric CO2 Enrichment, Master Resource (Apr. 21, 2022).
48 Nongovernmental International Panel on Climate Change (NIPCC), Climate Change Reconsidered II: Biological Impacts (2014) p. 322.

49 Craig Idso, Estimates of Global Food Production in The Year 2050: Will We Produce Enough to Adequately Feed the World?, p. 31 (2011).
50 Craig Idso, The Positive Externalities of Carbon Dioxide, CO2 COALITION (2013) p. 3 (discussed in Wrightstone, supra, p. 19).
51 One of the authors (Happer) explained that experiments with CO2 fertilization show that many crop yields increase by a factor x with adequate water and other nutrients, where x is the ratio of the current CO2 ppm level to the former level. Doubling from 400 to 800 ppm means x = 800/400 = 2, and √2 = 1.41, implying approximately a 40% increase. (Note it would take more than a century for CO2 to reach 800 ppm).
52 Quoted in NIPCC, Climate Change Reconsidered II: Fossil Fuels (2019), pp. 322–23.