The CSIRO-QCCCE contribution to CMIP5 using the CSIRO Mk3.6 climate model

Fifth phase of the Climate Model Intercomparison Project (CMIP5) is the principal framework for coordinated climate modeling experimentation supporting the preparation of the IPCC 5 Assessment Report to be released in 2013. About 20 modeling groups from around the world are undertaking the CMIP5 experiments and model data is being hosted on the Earth System Grid which consists of international data nodes and gateways (see http://cmip-pcmdi.llnl. gov/cmip5/). The CMIP5 experimental design features a standard set of model simulations consisting of simulations based on historical concentration and emission changes, simulations along potential future pathways to 2100, and a range of idealised experiments to understand climate sensitivity and to quantify key feedbacks. Projections of future climate are based on the new generation of emission scenarios, which were developed by the research community (Moss et. al., 2010). The CMIP5 experimental protocol provides four emission scenarios based on the Representative Concentration Pathways (RCPs), which are identified with their amounts of net radiative forcing input into the Earth's climate system at the end of the 21 Century. They include following scenarios:• A "no policy" RCP8.5 W/m ; • Two "stabilization" RCP6 W/m and RCP4.5 W/m ; • A "peak and decline" RCP2.6 W/m . CSIRO Marine and Atmospheric Research and the Queensland Climate Change Centre of Excellence (QCCCE) are contributing to this international project using the CSIRO-Mk3.6 Atmosphere Ocean Global Climate Model (AOGCM). The Mk3.6 climate model is a substantial upgrade from its recent predecessors Mk3.0 and Mk3.5, which were used to contribute to CMIP3. Upgrades included addition of an interactive aerosol scheme, which explicitly treats sulfate, dust, sea salt and carbonaceous aerosol. It also includes an updated radiation scheme and other changes to the atmospheric physics component. The CSIRO Mk3.6 climate model has been used to perform most of the long-term simulations which include the "core" experiments plus a number of "tier1" and "tier2" experiments specified by the CMIP5 experimental protocol (Taylor et al., 2011a). This paper shows selected results from historical simulations for the period 1851 to 2005 using various combinations of radiative forcing (both natural and anthropogenic) and results from climate change projections for the period 2006 to 2100. The analysis quantifies the relative contribution of various radiative forcing factors to the simulated changes in mean annual surface temperature during the 1981 to 2005 period. Results from the analysis show that simulations with natural forcing only resulted in small changes in the surface temperature, whereas the simulations with all forcing show statistically significant changes in the surface temperature over most of the Earth surface and these changes have magnitude comparable to observed changes. Furthermore, the rate of warming is greatest in the experiment with greenhouse gases only, where the cooling impact of anthropogenic aerosols is not accounted for. Model simulations show continuing warming and drying in subtropical land areas during the early part of 21 century

Aerosol- and greenhouse gas-induced changes in summer rainfall and circulation in the Australasian region: a study using single-forcing climate simulations

We use a coupled atmosphere-ocean global climate model (CSIRO-Mk3.6) to investigate the drivers of trends in summer rainfall and circulation in the vicinity of northern Australia. As part of the Coupled Model Intercomparison Project Phase 5 (CMIP5), we perform a 10-member 21st century ensemble driven by Representative Concentration Pathway 4.5 (RCP4.5). To investigate the roles of different forcing agents, we also perform multiple 10-member ensembles of historical climate change, which are analysed for the period 1951-2010. The historical runs include ensembles driven by "all forcings" (HIST), all forcings except anthropogenic aerosols (NO-AA) and forcing only from long-lived greenhouse gases (GHGAS). Anthropogenic aerosol-induced effects in a warming climate are calculated from the difference of HIST minus NO-AA. CSIRO-Mk3.6 simulates a strong summer rainfall decrease over north-western Australia (NWA) in RCP4.5, whereas simulated trends in HIST are weakly positive (but insignificant) during 1951-2010. The weak rainfall trends in HIST are due to compensating effects of different forcing agents: there is a significant decrease in GHGAS, offset by an aerosol-induced increase. Observations show a significant increase of summer rainfall over NWA during the last few decades. The large magnitude of the observed NWA rainfall trend is not captured by 440 unforced 60-yr trends calculated from a 500-yr pre-industrial control run, even though the model's decadal variability appears to be realistic. This suggests that the observed trend includes a forced component, despite the fact that the model does not simulate the magnitude of the observed rainfall increase in response to "all forcings" (HIST). We investigate the mechanism of simulated and observed NWA rainfall changes by exploring changes in circulation over the Indo-Pacific region. The key circulation feature associated with the rainfall increase in reanalyses is a lower-tropospheric cyclonic circulation trend off the coast of NWA, which enhances the monsoonal flow. The model shows an aerosol-induced cyclonic circulation trend off the coast of NWA in HIST minus NO-AA, whereas GHGAS shows an anticyclonic circulation trend. This explains why the aerosol-induced effect is an increase of rainfall over NWA, and the greenhouse gas-induced effect is of opposite sign. Possible explanations for the cyclonic (anticyclonic) circulation trend in HIST minus NO-AA (GHGAS) involve changes in the Walker circulation or the local Hadley circulation. In either case, a plausible atmospheric mechanism is that the circulation anomaly is a Rossby wave response to convective heating anomalies south of the Equator. We also discuss the possible role of air-sea interactions, e.g. an increase (decrease) of sea-surface temperatures off the coast of NWA in HIST minus NO-AA (GHGAS). Further research is needed to better understand the mechanisms and the extent to which these are model-dependent. In summary, our results suggest that anthropogenic aerosols may have "masked" greenhouse gas-induced changes in rainfall over NWA and in circulation over the wider Indo-Pacific region. Due to the opposing effects of greenhouse gases and anthropogenic aerosols, future trends may be very different from trends observed over the last few decades

The CSIRO-Mk3.6.0 Atmosphere-Ocean GCM: Participation in CMIP5 and data publication

The participation of the CSIRO-Mk3.6.0 Atmosphere Ocean Global Climate Model (AOGCM) in the Coupled Model Intercomparison Project Phase 5 (CMIP5) is a joint initiative between the Queensland Climate Change Centre of Excellence and the Commonwealth Scientific and Industrial Research Organisation (CSIRO). It now has approximately 10 research and support scientists working on this project which first began in 2009. This on-going project consists of the following four main components:• A model design and testing period to ensure that the model had acceptable configuration for participation in CMIP5, in particular, exhibiting a realistic present-day climate and a stable preindustrial climate;• A model integration phase where CMIP5 experiments were performed. These were to include the so-called "core" experiments plus a number of "tier1" and "tier2" experiments, which will constitute a significant submission to CMIP5 and to address local climate modelling needs and applications;• Post-processing of the raw CSIRO-Mk3.6.0 model output into internationally recognised and standardized CMIP5 form; and • Quality control and publication phase of the CSIRO-Mk3.6.0 data to ensure entry into the Earth System Grid (ESG) Federation, allowing it to be disseminated to the CMIP5 international community. In this paper the four phases of this climate modelling project will be discussed in detail. The main emphasis is to make potentially interested researchers aware of the CSIRO-Mk3.6.0 climate model submission and to elucidate the range and features of the datasets that are now available. The CMIP5 datasets are being hosted on the ESG which consists of international data nodes and gateways, including Australia's own node hosted by the National Computing Infrastructure (NCI) National Facility in Canberra. A key outcome of our efforts is the generation of over 150, mostly high priority, uniquely defined parameters from the list of requested model output to understand climate processes and also produce new climate change projection data for impact assessment. Some preliminary results of the CSIRO-Mk3.6.0 model are presented to illustrate the usefulness of this dataset in this research area