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Projecting the Impacts of Rising CO2 on Future Crop Yields in Germany

Paper Reviewed
Degener, J.F. 2015. Atmospheric CO2 fertilization effects on biomass yields of 10 crops in northern Germany. Frontiers in Environmental Science 3: 48, doi: 10.3389/fenvs.2015.00048.

Noting that the influence of atmospheric CO2 on crop growth is "still a matter of debate," and that "to date, no comprehensive approach exists that would represent all related aspects and interactions [of elevated CO2 and climate change on crop yields] within a single modeling environment," Degener (2015) set out to accomplish just that by estimating the influence of elevated CO2 on the biomass yields of ten different crops in the area of Niedersachsen, Germany over the course of the 21st century.

To accomplish this lofty objective the German researcher combined soil and projected future climate data (temperature and precipitation) into the BIOSTAR crop model and examined the annual difference in yield outputs for each of the ten crops (winter wheat, barley, rye, triticale, three maize varieties, sunflower, sorghum and spring wheat) under a constant CO2 regime of 390 ppm and a second scenario in which atmospheric CO2 increased annually through the year 2100 according to the IPCC's SRES A1B scenario. Degener then calculated the difference between the two model runs so as to estimate the quantitative influence of elevated CO2 on projected future crop yields. And what did that difference reveal?

As shown in the figure below, Degener reports that "rising [CO2] concentrations will play a central role in keeping future yields of all crops above or around today's level." Such a central, overall finding is significant considering Degener notes that future temperatures and precipitation within the model both changed in a way that was "detrimental to the growth of crops" (higher temperatures and less precipitation). Yet despite an increasingly hostile growing environment, according to the German researcher, not only was the "negative climatic effect balanced out, it [was] reversed by a rise in CO2" (emphasis added), leading to yield increases on the order of 25 to 60 percent.

Figure 1. Biomass yield difference (percent change) between model runs of constant and changing atmospheric CO2 concentration. A value of +20% indicates biomass yields are 20% higher when modeled using increasing CO2 values with time (according to the SRES A1B scenario of the IPCC) instead of a fixed 390 ppm for the entire run.

The results of this model-based study fall in line with the previous work of Idso (2013), who calculated similar CO2-induced benefits on global crop production by mid-century based on real-world experimental data, both of which studies reveal that any policy prescription designed to limit the upward trajectory of atmospheric CO2 concentrations will have very real, and potentially serious, repercussions for global food security.

Idso, C.D. 2013. The Positive Externalities of Carbon Dioxide: Estimating the Monetary Benefits of Rising Atmospheric CO2 Concentrations on Global Food Production. Center for the Study of Carbon Dioxide and Global Change, Tempe, AZ.

Posted 29 April 2016