Incorporating a modern understanding of soil carbon dynamics into Earth system model simulations

Over the past 20 years the understanding of carbon cycling within soils has radically advanced. However, the representation of soil carbon within Earth System Models has remained based on outdated models which do not reflect our current understanding of soil carbon processes. The Millennial version 2 soil carbon module was developed to allow Earth System Models to represent soil carbon processes such as microbial decomposition, aggregation, and mineral sorption. Millennial consists of five interacting soil carbon pools: particulate organic carbon, mineral-associated organic carbon, aggregate carbon, microbial biomass, and low molecular weight carbon, all of which can be measured in natural soils.

Here we have incorporated Millennial into the University of Victoria Earth System Climate model, an Earth system model of intermediate complexity, with a simplified atmosphere and full complexity land surface and ocean modules. Preliminary results suggest that Millennial generates soil carbon pools consistent with observations across regional climates and ecosystems. A series of model experiments have been devised to explore how soil carbon as simulated by Millennial behaves relative to traditional methods for simulating soil carbon.  Our experiments will show how much this higher fidelity soil carbon model structure will change projections of future climate change and remaining carbon budgets.