A study was conducted in the Open Top Chambers (OTCs) to assess the influence of cool and warm season conditions on the response of sunflower (KBSH-1) to two elevated CO 2 levels (550 and 700 ppm) and compare them with the response to an ambient level (390 ppm). The effect of elevated CO 2 levels on biomass accumulation seed yield and yield components were quantified in two seasons. Apart from the main effects of CO 2 and different seasons a significant interaction effect between CO 2 levels and seasons was also observed. The CO 2 levels differed significantly in influencing biomass accumulation seed yield and number of seeds. Four Principal Components (PC) based on PC analysis explained about 85% of the variability in the response of traits influenced by CO 2 levels in winter and summer seasons. In order to predict total dry weight seed yield and harvest index obtained in winter and summer seasons regression models of these variables were also calibrated and used through PC scores of different components. The analysis indicated that significant predictions could be made at ambient level with 550 ppm compared to 700 ppm of CO 2 level. The plant traits with a significantly higher loading of more than ± 0.70 on PCs were identified and have been recommended for future research in genetic improvement of sunflower taking into account the change of climate due to elevated CO 2 and temperature levels.