The Australian Community Climate and Earth System Simulator (ACCESS) has contributed to the World Climate Research Programme’s Coupled Model Intercomparison Project Phase 6 (CMIP6) using two fully coupled model versions (ACCESS-CM2 and ACCESS-ESM1.5) and two ocean–sea-ice model versions (1° and 0.25° resolution versions of ACCESS-OM2). The fully coupled models differ primarily in the configuration and version of their atmosphere components (including the aerosol scheme), with smaller differences in their sea-ice and land model versions. Additionally, ACCESS-ESM1.5 includes biogeochemistry in the land and ocean components and can be run with an interactive carbon cycle. CMIP6 comprises core experiments and associated thematic Model Intercomparison Projects (MIPs). This paper provides an overview of the CMIP6 submission, including the methods used for the preparation of input forcing datasets and the post-processing of model output, along with a comprehensive list of experiments performed, detailing their initialisation, duration, ensemble number and computational cost. A small selection of model output is presented, focusing on idealised experiments and their variants at global scale. Differences in the climate simulation of the two coupled models are highlighted. ACCESS-CM2 produces a larger equilibrium climate sensitivity (4.7°C) than ACCESS-ESM1.5 (3.9°C), likely a result of updated atmospheric parameterisation in recent versions of the atmospheric component of ACCESS-CM2. The idealised experiments run with ACCESS-ESM1.5 show that land and ocean carbon fluxes respond to both changing atmospheric CO2 and to changing temperature. ACCESS data submitted to CMIP6 are available from the Earth System Grid Federation (https://doi.org/10.22033/ESGF/CMIP6.2281 and https://doi.org/10.22033/ESGF/CMIP6.2288). The information provided in this paper should facilitate easier use of these significant datasets by the broader climate community.

The tropical Pacific Ocean interacts with the tropical Atlantic Ocean on interannual time scales. However, most coupled climate models misrepresent and/or underestimate these teleconnections, which have important implications on the periodicity of the El Niño‐Southern Oscillation (ENSO). Imposing the observed sea surface temperature over the tropical Atlantic from 1970 onwards, a pacemaker experiment is constructed using the second version of the Australian Community Climate and Earth System Simulator Coupled Model (ACCESS‐CM2). Compared with control runs which reasonably simulate the interaction between ENSO and the north tropical Atlantic variability, the pacemaker experiment significantly improves the impact of the Atlantic Niño/Niña on ENSO. This enhanced teleconnection contributes to a more realistic ENSO periodicity compared with the control runs, thus suggesting that capturing the influence from equatorial Atlantic variability is important for an improved ENSO simulation.

The westerly wind burst (WWB) is an important triggering mechanism of El Niño and typically occurs in the western Pacific Ocean. The Fourier spectrum of the wind field over the western tropical Pacific is characterised by a large variety of peaks distributed from intra-seasonal to decadal time scales, suggesting that WWBs could be a result of nonlinear interactions on these time scales. Using a combination of observations and simulations with 15 coupled models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), we demonstrate that the main drivers initiating WWBs are quantifiable physical processes rather than atmospheric stochastic signals. In this study, ensemble empirical mode decomposition (EEMD) from the Holo-Hilbert spectral analysis (HHSA) is used to decompose daily zonal winds over the western equatorial Pacific into seasonal, interannual and decadal components. The seasonal element, with prominent spectral peaks of less than 12 months, is not ENSO related, and we find it to be strongly associated with the East Asian monsoon (EAM) and cross-equatorial flow (CEF) over the Australian monsoon region. The CEF is directly related to the intensity of the Australian subtropical ridge (STR-I). Both the EAM and CEF are essential sources of these high-frequency winds over the western Pacific. In contrast, the interannual wind component is closely related to El Niño occurrences and usually peaks approximately two months prior to a typical El Niño event. Finally, the decadal element merely represents a long-term trend and thus has little to no relation to El Niño. We identified EAM- and CEF-induced westerly wind anomalies in December–January–February (DJF) and September–October–November (SON). However, these anomalies fade in March–April–May (MAM), potentially undermining the usual absence of WWBs in the boreal spring. Similar results are found in CMIP6 historical scenario data.

Observations revealed notable discrepancies in the 2023/24 El Niño compared to earlier events, despite registering moderate Niño3.4 index magnitudes. Essential indicators such as the westerly wind burst, thermocline zonal tilting, and eastward propagation of oceanic Kelvin waves were conspicuously weak, indicating a weak air‐sea coupled in contrast to past occurrences, the 2023/24 El Niño coincided with unusually high North Atlantic Tripole and extratropical North Pacific sea surface temperatures (SSTs). The elevated North Atlantic Tripole SST triggered a strong negative Pacific meridional mode and easterly anomalies in the equatorial western‐central Pacific. At the same time, the extratropical North Pacific SST induced a negative Pacific Decadal Oscillation‐like pattern. These anomalies potentially dampened SST‐wind coupling during the developmental stages of El Niño. The negative Pacific meridional mode distinguished the 2023/24 El Niño from previous events and substantially altered its local and remote influences.