The climate science community has tended to frame the attribution of individual extreme events through observed increases or decreases in the frequency of such events, where an observed change in frequency is consistent with background climate change. Typically, the community has also framed attribution questions by stating that it is not possible to attribute individual extreme events. Rather, extremes are caused by antecedent meteorological conditions and natural variability, as well as a likely contribution from climate change that is difficult to robustly quantify.

More recently, event attribution has sought to quantitatively deconstruct the contributions of various drivers of individual weather extremes, as well as determine the fraction attributable risk or likelihood of such events associated with the enhanced greenhouse effect.

We discuss various approaches for extreme event attribution and examine the record warm September experienced in Australia in 2013. Analysis using both multiple linear regression based on historical observational data and sensitivity experiments with a dynamical seasonal prediction system indicates that the record hot September 2013 in Australia arose from the apparently random occurrence of a strongly negative Southern Annular Mode (SAM) together with an anomalously deep low pressure cell situated to the southwest of the continent, the background warming trend and antecedent dry and warm land surface conditions. The results from the regression model indicate up to 15% of the record temperature anomaly in September 2013 can be explained by the global temperature changes over the 1982-2013 period analysed.