General circulation models (GCMs) project increases of the earth's surface air temperatures and other climate changes in the middle or latter part of the 21st century, and therefore crops such as cotton (Gossypium hirsutum L.) will be grown in a much different environment than today. To understand the implications of climate change on cotton production in the Mississippi Delta, 30 years (1964 to1993) of cotton growth and yield at Stoneville, Mississippi, USA, were simulated using the cotton simulation model GOSSYM. The GCM projections showed a nearly 4°C rise in average temperature and a decrease in precipitation during the crop growing season. The fertilization effect of an increase in atmospheric CO 2 concentrations from 360 to 540 ppm, without the change in other climatic variables, increased yields by 10% from 1563 to 1713 kg ha -1 , but when all projected climatic changes were included, yields decreased by 9% from 1563 to 1429 kg ha -1 . The rate of plant growth and development was higher in the future because of enhanced metabolic rates at higher temperatures combined with increased carbon availability. The effect of climate change on cotton production was more drastic in a hot and dry year. Since most of the days with average temperatures above 32°C will likely occur during the reproductive phase, irrigation will be needed to satisfy the high water demand, and this reduces boll abscission by lowering canopy temperatures. Therefore, if global warming occurs as projected, fiber production in the future environment will be reduced, and breeding heat-cold-tolerant cultivars will be necessary to sustain cotton production in the US mid-South. Cultural practices such as earlier planting may be used to avoid the flowering of cotton in the high temperatures that occur during mid to late summer.