labs_title

Caldeira Lab Research:Land Plants, Carbon, and Climate

Climate response to physiological forcing of carbon dioxide simulated by the coupled Community Atmosphere Model (CAM3.1) and Community Land Model (CLM3.0)

Long Cao, Govindasamy Bala, Ken Caldeira, Ramakrishna Nemani & George Ban-Weiss

An investigation of the physiological effects of doubled CO2 concentration on vegetation using the Community Atmospheric Model and the Community Land Model. The results are notably smaller than those produced in other simulations, possibly highlighting flaws in these models.


Cao, L., G. Bala, K. Caldeira, R. Nemani, and G. Ban-Weiss, 2009. Climate response to physiological forcing of carbon dioxide simulated by the coupled Community Atmosphere Model (CAM3.1) and Community Land Model (CLM3.0). Geophysical Research Letters, 36, L10402, doi:10.1029/2009GL037724.

Physiological effects of CO2 increase: Various effects of CO2 on vegetation graphed across the globe. Dotted areas represent parts of the world where the change is statistically significant.

Contributors to total evapotranspiration: The percentage contribution of various types of evaporation and transpiration to total global evapotranspiration. According to results from other models, this canopy transpiration is highly underestimated while the others are overestimated.

Abstract

Increasing concentrations of atmospheric CO2 decrease stomatal conductance of plants and thus suppress canopy transpiration. The climate response to this CO2-physiological forcing is investigated using the Community Atmosphere Model version 3.1 coupled to Community Land Model version 3.0. In response to the physiological effect of doubling CO2, simulations show a decrease in canopy transpiration of 8%, a mean warming of 0.1K over the land surface, and negligible changes in the hydrological cycle. These climate responses are much smaller than what were found in previous modeling studies. This is largely a result of unrealistic partitioning of evapotranspiration in our model control simulation with a greatly underestimated contribution from canopy transpiration and overestimated contributions from canopy and soil evaporation. This study highlights the importance of a realistic simulation of the hydrological cycle, especially the individual components of evapotranspiration, in reducing the uncertainty in our estimation of climatic response to CO2-physiological forcing.