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Over the last decade many climate models have evolved into Earth\udsystem models (ESMs), which are able to simulate both physical and\udbiogeochemical processes through the inclusion of additional components such\udas the carbon cycle. The Australian Community Climate and Earth System\udSimulator (ACCESS) has been recently extended to include land and ocean\udcarbon cycle components in its ACCESS-ESM1 version. A detailed description of\udACCESS-ESM1 components including results from pre-industrial simulations is\udprovided in Part 1. Here, we focus on the evaluation of ACCESS-ESM1 over the\udhistorical period (1850–2005) in terms of its capability to reproduce\udclimate and carbon-related variables. Comparisons are performed with\udobservations, if available, but also with other ESMs to highlight common\udweaknesses. We find that climate variables controlling the exchange of carbon\udare well reproduced. However, the aerosol forcing in ACCESS-ESM1 is somewhat\udlarger than in other models, which leads to an overly strong cooling response\udin the land from about 1960 onwards. The land carbon cycle is evaluated for\udtwo scenarios: running with a prescribed leaf area index (LAI) and running\udwith a prognostic LAI. We overestimate the seasonal mean (1.7 vs. 1.4) and\udpeak amplitude (2.0 vs. 1.8) of the prognostic LAI at the global scale, which\udis common amongst CMIP5 ESMs. However, the prognostic LAI is our preferred\udchoice, because it allows for the vegetation feedback through the coupling\udbetween LAI and the leaf carbon pool. Our globally integrated\udland–atmosphere flux over the historical period is 98 PgC for\udprescribed LAI and 137 PgC for prognostic LAI, which is in line with\udestimates of land use emissions (ACCESS-ESM1 does not include land use\udchange). The integrated ocean–atmosphere flux is 83 PgC, which is in\udagreement with a recent estimate of 82 PgC from the Global Carbon\udProject for the period 1959–2005. The seasonal cycle of simulated\udatmospheric CO<sub>2</sub> is close to the observed seasonal cycle (up to\ud1 ppm difference for the station at Mace Head and up to 2 ppm\udfor the station at Mauna Loa), but shows a larger amplitude (up to\ud6 ppm) in the high northern latitudes. Overall, ACCESS-ESM1 performs\udwell over the historical period, making it a useful tool to explore the\udchange in land and oceanic carbon uptake in the future

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