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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
doi:10.5194/gmd-2016-14
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Model evaluation paper
10 May 2016
Review status
A revision of this discussion paper is under review for the journal Geoscientific Model Development (GMD).
The carbon cycle in the Australian Community Climate and Earth System Simulator (ACCESS-ESM1). 2. Historical simulations
Tilo Ziehn1, Andrew Lenton2, Rachel M. Law1, Richard J. Matear2, and Matthew A. Chamberlain2 1CSIRO Oceans and Atmosphere, PMB 1, Aspendale, Victoria, Australia
2CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia
Abstract. Over the last decade many climate models have evolved into earth system models (ESMs), which are able to simulate both physical and biogeochemical processes through the inclusion of additional components such as the carbon cycle. The Australian Community Climate and Earth System Simulator (ACCESS) has been recently extended to include land and ocean carbon cycle components in its ACCESS-ESM1 version. A detailed description of ACCESS-ESM1 components including results from pre-industrial simulations is provided in Part 1. Here, we focus on the evaluation of ACCESS-ESM1 over the historical period (1850–2005) in terms of its capability to reproduce climate and carbon related variables. Comparisons are performed with observations, if available, but also with other ESMs to highlight common weaknesses. We find that climate variables controlling the exchange of carbon are well reproduced, however ACCESS-ESM1 is somewhat over-sensitive to anthropogenic aerosols which leads to an overly strong cooling response in the land from about 1960 onwards. The land carbon cycle is evaluated for two scenarios: running with a prescribed leaf area index (LAI) and running with a prognostic LAI. We overestimate the seasonal amplitude of the prognostic LAI at the global scale, which is common amongst CMIP5 ESMs. However, the prognostic LAI is our preferred choice, because it allows for the vegetation feedback through the coupling between LAI and the leaf carbon pool. Globally integrated land-atmosphere and ocean-atmosphere fluxes and flux patterns are well reproduced and show good agreement with most recent observations. The seasonal cycle of simulated atmospheric CO2 is close to the observed seasonal cycle, but shows a larger amplitude in the high northern latitudes. Overall, ACCESS-ESM1 performs well over the historical period, making it a useful tool to explore the change in land and oceanic carbon uptake in the future.

Citation: Ziehn, T., Lenton, A., Law, R. M., Matear, R. J., and Chamberlain, M. A.: The carbon cycle in the Australian Community Climate and Earth System Simulator (ACCESS-ESM1). 2. Historical simulations, Geosci. Model Dev. Discuss., doi:10.5194/gmd-2016-14, in review, 2016.
Tilo Ziehn et al.
Tilo Ziehn et al.
Tilo Ziehn et al.

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Our work presents the evaluation of the Australian Community Climate and Earth System Simulator (ACCESS-ESM1) over the historical period (1850–2005). The main focus is on climate and carbon related variables. Globally integrated land-atmosphere and ocean-atmosphere fluxes and flux patterns are well reproduced and show good agreement with most recent observations. This makes ACCESS-ESM1 a useful tool to explore the change in land and oceanic carbon uptake in the future.
Our work presents the evaluation of the Australian Community Climate and Earth System Simulator...
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