Regional Climate Response to Physiological Forcing of Carbon Dioxide in a Radiative-Convective Model

Distinct from its radiative forcing of the climate system, elevated carbon dioxide is likely to result in reduced stomatal conductance and transpiration over land surfaces - a biophysical effect that has been termed physiological forcing. Most studies done to quantify the magnitude of the climate response to physiological forcing have utilized 3D Global Atmosphere-Land Models; recently several have concluded that amplification due to cloud feedbacks could cause the surface air warming over some land regions due to physiological forcing to be as large as 20-30% of the total warming due to doubled CO2. Here, we use versions of a Radiative-Convective model with a very simple representation of a land surface in single- and multiple- column modes to broadly investigate the effect of surface conductance to water vapor on the overlying atmosphere. Due to the uncertainty of the magnitude of physiological forcing for a given change in CO2, we model simple land surfaces of varying wetness, from saturated to nearly completely dry. Reduced surface conductance to water vapor (e.g. physiological forcing) generally results in warming of the near-surface atmosphere, but the warming is not necessarily monotonic, and is sensitive to assumptions about clouds. Implications of our results for estimation of regional climate response to physiological forcing are discussed.