Elevated CO2 and the Sensitivity of Simulated Crop Yield to Variability in Climate

It is known that the response of crop yields to elevated carbon dioxide (CO₂) concentrations ('CO₂ fertilization') can vary with climatic conditions (e.g., precipitation and soil moisture). Likewise, the sensitivity of crop yield to changes in climate may vary with atmospheric CO₂ concentrations. The latter is an important consideration when extrapolating crop sensitivities derived from historical climate variability to a future world with higher levels of atmospheric CO₂. Here we report on our investigation of how climate sensitivity of model simulated crop yield is influenced by rising and elevated CO₂. Initial results from the EPIC crop model for simulated cotton yield at a site in southeastern Texas show very little if any difference in sensitivity to annual precipitation with static versus rising CO₂ concentrations. These model results are consistent with experimental results from the Maricopa, Arizona Free Air CO₂ Enrichment (FACE) experiment in which there was little or no difference in the productivity response of cotton under ample versus limited supplies of water. This contrasts with experimental results for wheat and sorghum, especially sorghum, in which the response to elevated CO₂ was larger when water supply was limited. We report on the interaction between CO₂ and the sensitivity of yield to climate with comparisons for different crops, between the EPIC and DSSAT crop models, across different indices of climate change, and between wet and dry climatic domains of the southern United States of America. This investigation is part of our ongoing effort better understand the sensitivity of crop yield to climate in order to inform regional integrated assessment modeling and considerations of adaption to climate change in the Gulf Coastal region of the southern United States.