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Growth and Yield Responses of Peanuts to Increases in Air Temperature and CO2 Concentration
Prasad, P.V.V., Boote, K.J., Allen Jr., L.H. and Thomas, J.M.G. 2003. Super-optimal temperatures are detrimental to peanut (Arachis hypogaea L.) reproductive processes and yield at both ambient and elevated carbon dioxide. Global Change Biology 9: 1775-1787.

What was done
In sunlit controlled-environment growth chambers maintained at atmospheric CO2 concentrations of 350 and 700 ppm and daytime-maximum/nighttime-minimum air temperatures of 32/22, 36/26, 40/30 and 44/34C, the authors grew peanuts (Arachis hypogaea L. cv. Georgia Green, of the Virginia Runner type) from seed to maturity, assessing various aspects of vegetative and reproductive growth along the way.

What was learned
(1) Leaf photosynthetic rates were unaffected by air temperature over the range studied; but they rose by approximately 27% in response to the experimental doubling of the air's CO2 content.

(2) Vegetative biomass increased by 51% and 54% in ambient-air and CO2-enriched air, respectively, as temperatures rose from 32/22 to 40/30C. A further temperature increase to 44/34C, however, caused moderate to slight declines in vegetative biomass in ambient and CO2-enriched air, respectively, so that the final biomass increase over the entire temperature range investigated was 27% in the ambient air and 53% in the CO2-enriched air. When going from the lowest temperature ambient CO2 treatment to the highest temperature elevated CO2 treatment, on the other hand, there was a whopping 106% increase in vegetative biomass.

(3) In contrast, seed yields in both ambient and CO2-enriched air dropped dramatically with each of the three temperature increases studied, declining at the highest temperature regime to but a small percentage of what they were at the lowest temperature regime. Nevertheless, Prasad et al. report that "seed yields at 36.4/26.4C under elevated CO2 were similar to those obtained at 32/22C under ambient CO2," the latter pair of which temperatures they describe as "present-day seasonal temperatures."

What it means
When all is said and done, it is clear that an unrealistically-large warming of 4.4C above present-day seasonal temperatures for peanut production would have essentially no effect on peanut seed yields, as long as the atmosphere's CO2 concentration rose concurrently, by something on the order of 350 ppm. It is also important to note, according to Prasad et al., that "maximum/minimum air temperatures of 32/22C and higher [our italics] are common [our italics] in many [our italics] peanut-producing countries across the globe." In fact, they note that "the Anantapur district in Andhra Pradesh, which is one of the largest peanut-producing regions in India, experiences season-long temperatures considerably greater [our italics] than 32/22C from planting to maturity [our italics]."

In light of these real-world observations, i.e., that some of the best peanut-producing regions in the world currently experience air temperatures considerably greater than what Prasad et al. suggest is optimum for peanuts (something less than 32/22C), it would appear that real-world declines in peanut seed yields in response to a degree or two of warming, even in air of ambient CO2 concentration, must be very slight or even non-existent (for how else could the places that commonly experience these considerably higher temperatures remain some of the best peanut-producing areas in the world?), which in turn suggests that for more realistic values of CO2-induced global warming, i.e., temperature increases on the order of 0.4C or less for a doubling of the air's CO2 content (Idso, 1998), there would likely be a significant increase in real-world peanut production.

Idso, S.B. 1998. CO2-induced global warming: a skeptic's view of potential climate change. Climate Research 10: 69-82.

Reviewed 3 March 2004