Cotton producers in the 21st century will be farming crops in different climates than today. Atmospheric CO₂ will likely exceed 700 ml l^-1 by the latter half of the next century, and the mean global temperature has been predicted to be 1.5 to 5.9°C higher than today. Further, the incidence of extreme weather events within a growing season has been predicated to increase. Extreme-weather events often limit crop yields even in today's environment; e.g., late spring frosts may severely limit citrus or winter wheat crops. Agricultural productivity is extremely sensitive to changes projected in the environment, particularly where crops are produced in marginal areas.

We conducted two experiments in which plants were grown in controlled environments with natural solar radiation. Temperature was varied in one experiment based on temperatures of the ambient environment during the whole season. In a second experiment, temperatures were referenced to long-term average July temperatures at Stoneville, MS. These temperatures were imposed only during the fruiting period. In both the experiments, CO₂ was also a variable while water and nutrients were supplied in abundance. Growth, development, and fruit production and retention were measured.

Seedling growth was considerably below the maximum at ambient temperature (23°C). Maximum seedling growth was at 30°C. Doubling atmospheric CO₂ concentration caused about 20% more dry matter to be produced in seedlings grown at near optimum temperature, but there was less CO₂ effect on seedlings grown at other temperatures. Developmental events: days to first square, flower, and open boll were very sensitive to temperature, but not to atmospheric CO₂ concentration. Developmental events were disproportionally slower at temperatures below 23°C. Flower and fruit production increased slightly as temperature increased, but fruit retention was very low or none at ambient plus 5°C and 7°C (31.3°C and 33°C). Production of cotton, and probably other seed-bearing crops, are predicted to be strongly damaged by temperatures above those presently found in the cottonbelt during the midsummer.