We tested the hypothesis that the effect of the role of CO2 change and soil moisture availability are interactively linked for all the GCM based vegetation types globally. A 1D atmospheric model dynamically coupled with a prognostic soil moisture / soil temperature scheme with a photosynthesis based vegetation / stomatal resistance submodel was used in this study. The objective was to analyze the effects of CO2 doubling, under high as well as limiting soil moisture conditions, over different terrestrial biomes. Results for all the nine global biomes, as defined through the SiB2 land cover classification, were analyzed for responses such as evapotranspiration, NPP or net carbon assimilation, stomatal resistance, and air temperature. Results confirm the observations that CO2 and soil moisture related effects are critical for both the C3 and C4 plants. In particular the study highlights the role of soil moisture and CO2 interactions as a key component of the terrestrial ecosystem. Our results also indicate that (a) explicit resolution of the direct and interactive effects associated with the input variable changes are useful measures for assessing the effects due to CO2 changes; (b) resolving the interactions explicitly, both C3 and C4 vegetation will be significantly affected by the CO2 changes; and not support a conclusion that C4 may not be significantly affected; (c) studies linking CO2 effects in a sensitivity - type analysis both in observational as well as numerical experiments should explicitly resolve the interactions. Thus, impacts associated with CO2 doubling cannot be assessed without considering the soil moisture status. As that, each vegetation type has a different strategy to account for CO2 changes with regard to soil moisture availability. Events such as drought or high soil moisture availability can enhance, or completely balance, or even reverse the effects associated with CO2 doubling by itself, and needs to be considered in any comprehensive future assessment. Often, despite dramatic leaf level impacts due to climate changes, the natural ecosystem tends to buffer and does not show a dramatic response. Our analysis suggests that the interactions between the biotic and abiotic changes tend to have a compensatory / antagonistic response. This reduces the effect of the variable change on the overall system response.