Climate change and its impact on crop productivity is a burning issue of the day .according to predictions of international panel on climate change (IPCC) and Pakistan Meteorological Department (PMD) these changes are taking place very rapidly on global level and affecting crop productivity. Their predictions are based on long term past climate data analysis with the help of general circulation models (GCMS).The aim of present study was to calibrate and validate CSM-Crop-Grow Cotton Model in DSSAT V 4.0.2. to simulate development, growth, and yield of cotton (Gossypium hirsutum L) under increased CO 2 concentration, elevated temperatures and varying rainfall scenarios. For these purpose field trials at three locations were conducted with two sowing dates, four cotton cultivars and four nitrogen levels with split-split plot design having three replications during year 2005 and 2006. The data on phenology, growth and yield were recorded and used for model calibration during 2005 (Genetic co-efficient of four cotton cultivars were determined).The model was then validated with independent set of data collected during year 2006 with same set of coefficient, long term past historic climate data of three locations (1974-2006), soil and crop management data used as input data for model and environmental modification sub menu of seasonal tool selected various climate change scenarios viz current i-e no change in environment. Elevated temperatures of + 0.9 O C and 1.8 O C, increased concentrations of CO 2 from 360 ppm to 550 ppm with no change in rainfall and increased / decreased 3% , 6% levels of rainfall expected in 2025 & 2050. The results indicated that model successfully simulated 80-90 % crop phenology and growth and 90-98 % yield accurately at various sites and can be used as reliable agronomic tool for strategy management in future. The elevated CO 2 levels would effect cotton crop growth and yield positively on all locations. Climate change analysis indicated strong influence of temperature on cotton production in Punjab, Pakistan. The yield will be substantially decreased with increasing temperature 1.8 O C and the effect was more severe at xviiilocations like Sahiwal. Increasing or decreasing 6% rainfall would affect cotton growth and yield negatively and drastic yield reductions were observed from the current. Selection of suitable cultivar, changing sowing time and nitrogen application are helpful in mitigation of adverse effects of changed climate of 2025-2050. Dominance analysis of different planting dates and cultivars at various locations suggested that 60 days early sowing of cotton crop from current at Faisalabad and Sahiwal with cultivar SLH-284, N applied @ 200 kg ha -1 is the best choice under changed climate scenarios (2050) whereas cultivar CIM -506 with nitrogen rate of 200 kg ha -1 out yielded all other cultivars when sown 15 days late from current at Multan location under changed climate scenario of 2050.