Impacts of leaf traits on vegetation optical properties in Earth system modeling

Quantifying surface energy and carbon budgets is essential for projecting Earth's climate. Earth System Models (ESMs) typically simulate land surface processes based on plant functional types (PFTs), neglecting the diversity of plant functional traits or characteristics (PFCs; e.g., chlorophyll content and leaf mass per area). Here, we demonstrate substantial differences in modeled leaf optical properties (LOP) and surface albedo between traditional PFT-based and PFC-based approaches, particularly in tropical and boreal forests. We configure the canopy radiative transfer scheme in the Community Earth System Model using PFC-based LOP. This new configuration produces lower shortwave surface albedo in the tropics but higher albedo in boreal regions (>5 W m^-2 radiative flux differences), and a weaker tropical but stronger boreal carbon sink. Through land-atmosphere coupling, the PFC-based configuration further alters atmospheric processes, leading to different temperature, cloud cover, and precipitation patterns. Our findings highlight the need to move beyond traditional PFT-based approaches in ESMs.