The Australian Community Climate and Earth System Simulator, ACCESS, has been developed over recent years for numerical weather prediction and for climate simulations. Following the successful submission of ACCESS climate simulations to the Coupled Model Intercomparison Project (CMIP5), the next major development for ACCESS is the inclusion of the carbon cycle. This will allow the feedback between the climate and the carbon cycle to be explored. The feedback is generally considered to be positive but with uncertain magnitude.
Component models for land and ocean carbon have been developed and tested in atmosphere-only and ocean-only simulations respectively, and in a low resolution coupled model. Land carbon is simulated as part of the Community Atmosphere Biosphere Land Exchange (CABLE) model with biogeochemistry that also includes nitrogen and phosphorus cycles. The ocean carbon model, WOMBAT (World Ocean Model of Biogeochemistry And Trophic-dynamics) includes a two-component plankton model (phytoplankton and zooplankton) where the phytoplankton growth is controlled by phosphate and iron concentrations, light and temperature.
Here we will present initial results from the fully coupled ACCESS-carbon cycle system. Simulations are run with prescribed atmospheric CO₂, firstly for pre-industrial conditions to ensure stability of the simulated carbon fluxes and secondly for historically increasing atmospheric CO₂. The simulated land and ocean carbon uptake over the last four decades, gross primary production, plant and soil carbon pools and atmospheric CO₂ will be compared with independent estimates.