School of Earth Sciences - Research Publications

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Author: Karoly, David × Author: Lewis, Sophie ×

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    THE ROLE OF ANTHROPOGENIC FORCING IN THE RECORD 2013 AUSTRALIA-WIDE ANNUAL AND SPRING TEMPERATURES
    Lewis, SC ; Karoly, DJ (AMER METEOROLOGICAL SOC, 2014-09)
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    Evaluation of Historical Diurnal Temperature Range Trends in CMIP5 Models
    Lewis, SC ; Karoly, DJ (AMER METEOROLOGICAL SOC, 2013-11)
    Abstract Diurnal temperature range (DTR) is a useful index of climatic change in addition to mean temperature changes. Observational records indicate that DTR has decreased over the last 50 yr because of differential changes in minimum and maximum temperatures. However, modeled changes in DTR in previous climate model simulations of this period are smaller than those observed, primarily because of an overestimate of changes in maximum temperatures. This present study examines DTR trends using the latest generation of global climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) and utilizes the novel CMIP5 detection and attribution experimental design of variously forced historical simulations (natural-only, greenhouse gas–only, and all anthropogenic and natural forcings). Comparison of observed and modeled changes in DTR over the period of 1951–2005 again reveals that global DTR trends are lower in model simulations than observed across the 27-member multimodel ensemble analyzed here. Modeled DTR trends are similar for both experiments incorporating all forcings and for the historical experiment with greenhouse gases only, while no DTR trend is discernible in the naturally forced historical experiment. The persistent underestimate of DTR changes in this latest multimodel evaluation appears to be related to ubiquitous model deficiencies in cloud cover and land surface processes that impact the accurate simulation of regional minimum or maximum temperatures changes observed during this period. Different model processes are likely responsible for subdued simulated DTR trends over the various analyzed regions.
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    Anthropogenic contributions to Australia's record summer temperatures of 2013
    Lewis, SC ; Karoly, DJ (AMER GEOPHYSICAL UNION, 2013-07-28)
    Abstract Anthropogenic contributions to the record hot 2013 Australian summer are investigated using a suite of climate model experiments. This was the hottest Australian summer in the observational record. Australian area‐average summer temperatures for simulations with natural forcings only were compared to simulations with anthropogenic and natural forcings for the period 1976–2005 and the RCP8.5 high emission simulation (2006–2020) from nine Coupled Model Intercomparison Project phase 5 models. Using fraction of attributable risk to compare the likelihood of extreme Australian summer temperatures between the experiments, it was very likely (>90% confidence) there was at least a 2.5 times increase in the odds of extreme heat due to human influences using simulations to 2005, and a fivefold increase in this risk using simulations for 2006–2020. The human contribution to the increased odds of Australian summer extremes like 2013 was substantial, while natural climate variations alone, including El Niño Southern Oscillation, are unlikely to explain the record temperature.
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