Dynamic vegetation reveals unavoidable climate feedbacks and their dependence on climate mean state

Abstract. We investigate seasonal vegetation feedbacks considering mid-Holocene and pre-industrial simulations with the IPSL climate models for which dynamic vegetation is switch on. We consider four different settings for the land surface model designed to improve the representation of boreal forest. They combine different choices for bare soil evaporation, photosynthesis and associated parameters, and tree mortality. Whatever the model set up, the major seasonal differences expected between the mid Holocene and preindustrial climates remain similar, and consistent with the mid Holocene greening of the Sahara and northward shift of the northern limit of forest in the northern hemisphere. However, the way vegetation-climate interactions trigger unavoidable radiative surface albedo and water vapor feedbacks depend on the model content. Cascading feedbacks involve local snow-vegetation interactions, as well as remote water vapor and long wave radiative feedbacks in the tropics, which are needed to fulfill the global energy conservation constraint of the climate system. We show that the parameterization of bare soil evaporation is a key factor that control tree growth in mid and high latitudes. Photosynthesis parameterization appears to be critical in controlling the functioning of vegetation and vegetation-climate interactions. It affects the seasonal evolution of the vegetation and leaf area index, as well as their effect on radiative feedbacks and the sensitivity of the vegetation feedback to the climate mean state. This sensitivity needs to be considered when developing and tuning climate models.