Global climate model simulations used for these projections come from the international Coupled Model Intercomparison Project Phase 5 (CMIP5 ). A list of the global climate models used in these projections can be found here .
Model results from the CMIP5 ensemble are complemented here with some fine resolution downscaled data. Two new sets of downscaling (one statistical and one dynamical) results are used, and downscaled results from some previous regional studies are also consulted. The downscaled data do not play a major role in these projections, with their role confined to the assessment of confidence in the global climate model-based projections (Technical Report Section 7.2), and as sources for (projected climate change data applied to observations) in some circumstances where the added value was clearly established (Technical Report Section 6.3.2). This site contains more information on the use of and on .
Climate models were assessed as to how well they simulated aspects of current climate (). Although models varied considerably in their skill, no subset of climate models performed well across all metrics and there was not a strong link between model evaluation results and projected changes ( ). Consequently, a skill-based weighting was not applied and all available simulations were considered in preparing quantitative ranges of projected change. However, model evaluation results were used in informing selection of individual models for the development of application-ready data sets.
A sample of eight CMIP5 models, from a total of 40, has been selected for use in climate change impact assessments, ensuring that the range of change in the smaller sample is representative of the broader range of results for Australia, while also considering model skill and model genealogy.The method used for selection of these models is described in Chapter 9 of the Technical Report and here .
Projected changes are given for a range of emission scenarios as defined by the(RCPs) used by the IPCC. These scenarios range from RCP2.6 with low emissions and ambitious and sustained global emissions reduction, to RCP8.5, a high-emission scenario with ongoing increase in emissions beyond the 21st century.
Projected changes are calculated based on area-averaged data for each of Technical Report Section 6.2.2). In addition to model ranges, changes for individual models are also available on the website. of simulated climate change (1901 to 2099) against a longer baseline (1950-2005) are also presented within this work to illustrate the interplay between the slowly emerging climate change signal and natural internal variability.covering the entire nation. These projections are presented as ranges of change for different 20-year time periods in the future with respect to the reference period (1986-2005). Generally, the 10th to 90th percentile range of the distribution of CMIP5 global climate model results is used to characterise the projections (
The approach used here differs from that used in the 2007 Climate Change in Australia projections () in a number of technical aspects mainly related to how natural climatic variability is represented in the projections. Projected ranges of change presented here include differences from the baseline due to natural variability as well as changes due to enhanced greenhouse conditions, whereas this was not the case in CCIA 2007.
A list of climate variables available from this website can be found here . For some variables, selected measures of frequency or intensity of extremes are included as well as mean conditions. A range of products is available for most of the variables. However, in some cases only qualitative information (e.g. direction of change) is highlighted, as confidence in the reliability of quantitative information from the climate models was low.
Page updated 20th December 2020