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One of the major issues of global concern today is rapidly increasing levels of CO2 in the atmosphere and its potential to change the world climate. It is important to understand how different agricultural cultivars will respond to different projected future levels of elevated CO2 and its association with increasing temperatures. In this experiment, there were examined single and combined effects of different CO2 levels (ambient 350 ppm, 700, 1 500 and 3 000 ppm) and elevated temperature (ambient +4 °C-day/5 °C-night) on barley (Hordeum vulgare L. cv. 'Aura') and tomato (Lycopersicon esculentum Mill. cv. 'Svara') growth characteristics. Experiments were conducted in the closed environment-controlled chambers. The results showed that the current ambient level of atmospheric CO2 concentration was a growth limiting factor for the investigated agricultural species. Under single CO2 effect the greatest biomass accumulation of both plants was observed at 1 500 ppm concentration. However the highest investigated concentration of CO2 (3 000 ppm) significantly stimulated only biomass of barley. The highest biomass accumulation was detected under combined effect of elevated CO2 and temperature, when the increases were 43.0 and 37.6% (p < 0.05) for barley and tomato respectively, compared to reference treatment. The factorial Anova analysis of all measured indices of investigated plants showed that the prior climate factor for barley was elevated CO2 (700 ppm) while the effect of increased temperature (ambient +4 °C-day/5 °C-night) was much weaker. Whereas for tomato, which is considered as warmth-loving plant, substantial climate factor was elevated temperature, and the effect of 700 ppm CO2 had a markedly weaker input. [ABSTRACT FROM AUTHOR]