A Comparison of Scenarios for the Effect of Global Climate Change on Cotton Growth and Yield

If global surface temperatures change as projected because of radiative and physiological effects of a changing environment, we should expect important changes in crop production in the 21st Century. Experiments were conducted at ambient and twice ambient atmospheric CO2 concentrations at five temperatures. The 1995 temperature in Mississippi was used as a reference with the other temperatures being 1995 minus 2˚C, and 1995 plus 2, 5 and 7˚C. Daily and seasonal variation and amplitudes were maintained. Seedlings had 4–6 times as much leaf area and dry weight at 20 d after emergence when grown at 28˚C as at 23˚C (1995 ambient) average temperature during that growth period. Number of days to first square, flower, and open boll decreased as temperature increased. Double atmospheric CO2 did not affect these developmental rates. Temperatures above 28˚C, or 1995 average whole-season temperatures, were detrimental to mid- and late-season boll retention and growth. No fruits were retained to maturity at 1995 plus 5 or 7˚C. However, whole season vegetative growth was not significantly reduced by temperature 5–7˚C above the 1995 ambient conditions. Twice ambient CO2 caused about 40% increase in vegetative dry matter accumulation across temperatures. In a separate experiment, similar results were obtained on fruiting cotton grown at a range of temperatures based on long-term average US Midsouth July temperatures. Therefore, if global warming occurs as predicted, food and fibre production in such high-temperature and humid environments may be more limited to vegetative structures and the animals that consume vegetative structures.