A new modeling method to quantify aerosol-induced vegetation-climate biophysical feedbacks

Atmospheric aerosols can strongly affect vegetation through their cooling effect and changing diffuse radiation. The changes of vegetation further alter the climate through biophysical and biochemical feedbacks. Previous studies either investigate aerosol impacts in offline simulations to understand the vegetation response, or in fully coupled simulations to quantify the full impacts on the climate, including through atmospheric physics. So far there has been no experiment designed to separate the aerosol-induced vegetation-climate feedback from the aerosol impact itself. Existing studies on vegetation-climate feedbacks (not necessarily due to aerosol) often prescribe vegetation properties, so that the climate altered by vegetation can no longer affect the vegetation, leading to an incomplete feedback estimation. To quantify the full vegetation-climate feedback due to aerosols, we propose a new modeling framework in coupled Earth system models (ESM). In this new framework, the atmosphere module simulates the climate under both preindustrial and historical aerosol scenarios at each time step. The climates simulated under the two scenarios are both passed to the land surface module. All processes in the land surface module are separated into an organic (vegetation, part of soil) and an inorganic (energy budget, hydrology) part. The organic part is driven by the preindustrial aerosol climate, while the inorganic part is driven by the historical aerosol climate and affected by the organic part. The land surface processes provide the feedback variables for atmosphere to simulate the next time step. The feedback can be evaluated by comparing this experiment to fully coupled simulations under preindustrial and historical aerosol scenarios. Here we first introduce this framework and apply it to IPSL-CM6A-LR ESM. This new framework can have more general usages and provide opportunities to understand the land surface feedbacks in the Earth system.