Analysing CO2 and soil moisture Variability in a Climatological Perspective

One of the most uncertain factors in assessing climate change is understanding the impact associated with enhanced carbon dioxide availability. In recent years, there has been significant data on the effect of CO2 changes on the terrestrial ecosystem. The datasets provide contradictory evidence on the role increased CO2 will have on the climate, particularly on surface temperature (warming or cooling), water use efficiency (drought), and regional productivity (through altered photosynthetic capacity). We hypothesize that, one of the reasons for this contradictory evidence is the highly interactive nature of the CO2 related effects. For instance, the enhanced CO2 level can cause reduction in the evapotranspirative loss from the vegetation while the high soil moisture availability will induce the plant to adopt a more liberal and less efficient water use strategy resulting in higher evapotranspiration. In addition to these first order effects of the terrestrial components, there can be conflicting nonlinear or second order effects (aiding or precluding evapotranspiration) antagonistically apropos the direct effects. Using GEM, a coupled gas exchange evapotranspiration model with a high resolution PBL model, a statistical experiment is designed to investigate explicit interactions between differential soil moisture availability with varying carbon dioxide levels in a fully coupled mode (two way coupling between the surface and the atmosphere). The implications of this type of analysis and the resulting explicit direct and indirect forcing on climate change simulations will be presented.