Quantitative estimates of anthropogenic contributions to extreme national and State monthly, seasonal and annual average temperatures for Australia

Abstract

Extreme event attribution studies can provide valuable information for assessing the risks and costs of future climate change. However, the utility of such information for adaptive decision-making depends on reliable information being provided in a timely manner. Here, we present pre-computed Fraction of Attributable Risk (FAR) tables for various Australian temperature records, as an estimate of the change in likelihood of exceeding defined temperature thresholds that can be attributed to anthropogenic influences, such as long-lived greenhouse gases. Australian and State-based area-average mean, maximum and minimum temperature anomalies are considered. The likelihoods of extreme annual, seasonal and monthly temperatures occurring in a suite of Coupled Model Intercomparison Project phase 5 (CMIP5) simulations incorporating only natural forcings (solar and volcanic aerosols) are compared with the likelihoods from simulations including both natural and anthropogenic (greenhouse gases, aerosols and ozone) forcings. This approach provides a simple tool for the timely assessment of the contribution of anthropogenic factors to record-setting temperatures for different Australian regions. In the case when an existing national or State-wide temperature record is exceeded, the FAR 'look-up' data tables presented here provide an immediate source of information about the change in risk of such an event occurring that can be attributed to anthropogenic influences. In all regions, the FAR values demonstrate that the likelihood of warmer conditions on various timescales has increased due to anthropogenic forcings. The FAR values presented here will be most useful if updated to reflect future changes in anthropogenic forcings and using new record-setting temperature anomalies.