Insights From CMIP6 for Australia's Future Climate

Abstract

Outputs from new state-of-the-art climate models under the Coupled Model Inter-comparison Project phase 6 (CMIP6) promise improvement and enhancement of climate change projections information for Australia. Here we focus on three key aspects of CMIP6: what is new in these models, how the available CMIP6 models evaluate compared to CMIP5, and their projections of the future Australian climate compared to CMIP5 focussing on the highest emissions scenario. The CMIP6 ensemble has several new features of relevance to policymakers and others, for example, the integrated matrix of socioeconomic and concentration pathways. The CMIP6 models show incremental improvements in the simulation of the climate in the Australian region, including a reduced equatorial Pacific cold tongue bias, slightly improved rainfall teleconnections with large-scale climate drivers, improved representation of atmosphere and ocean extreme heat events, as well as dynamic sea level. However, important regional biases remain, evident in the excessive rainfall over the Maritime Continent and rainfall pattern biases in the nearby tropical convergence zones. Projections of Australian temperature and rainfall from the available CMIP6 ensemble broadly agree with those from CMIP5, except for a group of CMIP6 models with higher climate sensitivity and greater warming and increase in some extremes after 2050. CMIP6 rainfall projections are similar to CMIP5, but the ensemble examined has a narrower range of rainfall change in austral summer in Northern Australia and austral winter in Southern Australia. Overall, future national projections are likely to be similar to previous versions but perhaps with some areas of improved confidence and clarity.

The differing role of weather systems in southern Australian rainfall between 1979–1996 and 1997–2015

“…Projections from global climate models consistently show a continued future decline in cool season rainfall in both SWWA and SEA (Grose et al 2020;Hope et al 2015). The frequency of cyclones is also expected to decline in Australian latitudes (Grieger et al 2014;Utsumi et al 2016), although projections of all fronts (both cold and warm) are less certain (Catto et al 2014).…”

Comparison of past and future simulations of ENSO in CMIP5/PMIP3 and CMIP6/PMIP4 models

“…Carré et al, 2014;Conroy et al, 2008;Donders et al, 2005;Koutavas and Joanides, 2012;Koutavas et al, 2006;McGregor and Gagan, 2004;McGregor et al, 2013;Rein et al, 2005;Riedinger et al, 2002;Tudhope et al, 2001;White et al, 2018). Cobb et al (2013) argued that coral records from the central Pacific do not show a statistically significant reduction in mid-Holocene ENSO variability but a new ensemble of central Pacific records (Grothe et al, 2019) provides evidence for a significant reduction from 3 to 5 ka. Some studies have suggested that disagreement between the magnitude of mid-Holocene ENSO reduction in different proxy records may be due to shifts in the spatial pattern of ENSO variability between the eastern and central Pacific (e.g.…”

Evaluation of Historical CMIP6 Model Simulations of Seasonal Mean Temperature over Pakistan during 1970–2014

“…The diagnostic, evaluation, and characterization of Klima (DECK) experiments and historical simulations are developed under different forcings scenarios of past climates. The five newly developed future scenarios of CMIP6, i.e., shared socioeconomic pathways (SSPs), follow the pre-industrial and CO 2 forcings of CMIP5-RCPs with new forcings included subsequent to industrial, socioeconomic policy, technological, and human-induced impacts on the climate [24][25][26].…”

“…The CMIP6 models exhibit higher sensitivity to greenhouse gases (GHG) emissions compared to CMIP5 [27]. Grose et al [26] observed CMIP6 has improved aerosols' effect, models' resolution, parameterization schemes, and more earth system models included. CMIP6 differs from CMIP5 with higher model climate sensitivity to GHG concentrations, contribution of different aerosols in GHGs, and aerosol forcing-based scenarios.…”