Climate change will have a major bearing on survival and development of insects as a result of increase in CO₂ and temperature. Therefore, we studied the direct effects of CO₂ and temperature on larval development and metabolism in cotton bollworm, Helicoverpa armigera (Hübner). The larvae were reared under a range of CO₂ (350, 550, and 750 ppm) and temperature (15, 25, 35, and 45°C) regimes on artificial diet. Elevated CO₂ negatively affected the larval survival, larval weight, larval period, pupation, and adult emergence, but showed a positive effect on pupal weight, pupal period, and fecundity. Increase in temperature exhibited a negative effect on larval survival, larval period, pupal weights, and pupal period, but a positive effect on larval growth. Pupation and adult emergence were optimum at 25°C. Elevated CO₂ and temperature increased food consumption and metabolism of larvae by enhancing the activity of midgut proteases, carbohydrases (amylase and cellulase), and mitochondrial enzymes and therefore may cause more damage to crop production. Elevated CO₂ and global warming will affect insect growth and development, which will change the interactions between the insect pests and their crop hosts. Therefore, there is need to gain an understanding of these interactions to develop strategies for mitigating the effects of climate change.