Global climate change the looming environmental threat is mainly due to the increase in atmospheric CO 2 levels, which was increasing earlier by about 1.55 ppm per year and currently by 2.76 ppm per year. Thus, CO 2 concentration has reached 400.16 ppm in 2015. To understand the response of various tropical tree species to such an elevated CO 2 , experiments were conducted in Automated Open Top Chambers (AOTC) facility at Institute of Forest Genetics and Tree Breeding (IFGTB), Coimbatore (India). The results of initial studies indicated the scope for exploring intraspecific variation in response of tropical trees to elevated CO 2 . Subsequently, experiments were carried out to assess intra-specific variation in Neem (Azadirachta indica). The selected phenotypes of Neem (varieties or clones) were exposed to four treatments viz., i) CO 2 of 600 ppm, ii) CO 2 of 900 ppm, iii) chamber control-without any CO 2 enrichment and iv) ambient conditions. The parameters studied were shoot length, root length, dry matter accumulation in shoot and root.