Environmental Science and Engineering Seminar

Plant physiological responses to increasing atmospheric CO2 concentration (iCO2) have been extensively explored using in-situ experiments and ecosystem models. However, the coupling of this mechanism with the climate system has only been explored using Earth system models (ESMs) more recently. Important questions emerge, such as how large the feedback from plant physiological response to iCO2 is compared to changed climate caused by greenhouse gas effects and whether this feedback generates new climate-carbon feedback both regionally and globally. In this presentation, I will review the current understanding of model-simulated temperature and hydrological changes induced by plant physiological responses to iCO2. Idealized CMIP5 and CMIP6 model simulations of a non-linear 1 % per year iCO2 show widespread decreases in stomatal conductance and transpiration, which, in turn, amplify climate warming and alter precipitation patterns across tropical continents. Taking Amazonia as an example, I provide evidence that plant physiology accounting for regional precipitation decline, decrease in surface relative humidity, and warming can be large enough to cause the loss of the aboveground carbon storage through increased water stress, enhanced fire risks, and increased thermal stress of tropical forests. Though multiple sources of uncertainty make it challenging to robustly quantify the magnitude of these effects or their subsequent impact on vegetation carbon storage, these model results provide insight into the next step of quantifying ecosystem impacts of plant physiological responses to iCO2. This is particularly important to be discussed in the context of natural climate solutions such as avoiding deforestation and reforestation programs as the carbon consequences of these efforts may be different under varied CO2 levels.