The carbon cycle in the Australian Community Climate and Earth System Simulator (ACCESS-ESM1) – Part 1: Model description and pre-industrial simulation

Abstract

Abstract. Earth system models (ESMs) that incorporate carbon-climate feedbacks represent the present state of the art in climate modelling. Here, we describe the Australian Community Climate and Earth System Simulator (ACCESS)-ESM1, which comprises atmosphere (UM7.3), land (CABLE), ocean (MOM4p1), and sea-ice (CICE4.1) components with OASIS-MCT coupling, to which ocean and land carbon modules have been added. The land carbon model (as part of CABLE) can optionally include both nitrogen and phosphorous limitation on the land carbon uptake. The ocean carbon model (WOMBAT, added to MOM) simulates the evolution of phosphate, oxygen, dissolved inorganic carbon, alkalinity and iron with one class of phytoplankton and zooplankton. We perform multi-centennial preindustrial simulations with a fixed atmospheric CO 2 concentration and different land carbon model configurations (prescribed or prognostic leaf area index). We evaluate the equilibration of the carbon cycle and present the spatial and temporal variability in key carbon exchanges. Simulating leaf area index results in a slight warming of the atmosphere relative to the prescribed leaf area index case. Seasonal and interannual variations in land carbon exchange are sensitive to whether leaf area index is simulated, with interannual variations driven by variability in precipitation and temperature. We find that the response of the ocean carbon cycle shows reasonable agreement with observations. While our model overestimates surface phosphate values, the global primary productivity agrees well with observations. Our analysis highlights some deficiencies inherent in the carbon models and where the carbon simulation is negatively impacted by known biases in the underlying physical model and consequent limits on the applicability of this model version. We conclude the study with a brief discussion of key developments required to further improve the realism of our model simulation.

The carbon cycle in the Australian Community Climate and Earth System Simulator (ACCESS-ESM1) – Part 2: Historical simulations

“…1). Law et al (2017) also showed that the climate simulations of the three model versions are very similar.…”

“…A selection of CMIP5 simulations have now been performed with the ESM version of AC-CESS, ACCESS-ESM1 (Law et al, 2017). Here, we present the performance of the land and ocean carbon cycle components of ACCESS-ESM1 over the historical period .…”

“…The climate model version underlying the ESM version is ACCESS1.4, a minor update of the AC-CESS1.3 version submitted to CMIP5 Dix et al, 2013). The relationship between the ACCESS1.3, AC-CESS1.4 and ACCESS-ESM1 versions is illustrated in Law et al (2017, Fig. 1).…”

“…As in Law et al (2017), two model configurations are used, differing in their treatment of LAI. LAI is an important variable in climate models for describing the biophysical and biogeochemical properties of the land cover and in CABLE it can either be prescribed or simulated.…”

“…ACCESS-ESM1 is based on the ACCESS climate model , but with the addition of biogeochemical components for ocean and land as described in Part 1 of this paper (Law et al, 2017). The climate model version underlying the ESM version is ACCESS1.4, a minor update of the AC-CESS1.3 version submitted to CMIP5 Dix et al, 2013).…”