Cotton lint yields in the 25 Texas High Plains counties have declined at a linear rate of 9.4 kg ha^-1 year^-1 for an estimated total decline from 1965-1985 of 197 kg ha^-1. Simulations using reduced input levels of 10.2 cm irrigation (4.0 inches) and of 12 kg N/ha (11 lbs,/acre) estimate a lint yield reduction of 161 kg ha during the same period. Simulated effects of weather, carbon dioxide, ozone, and herbicides indicated a potential yield increase of 37 kg ha. The input reductions of nitrogen and irrigation used in the simulations were estimated from historical data. The simulated effects of carbon dioxide, ozone, and especially herbicide involved considerable extrapolation of historical data and interpretation of research concerning the effect of these factors on cotton growth and development. Therefore, the simulated effects of nitrogen and irrigation were considered more reliable than those of the other factors.