Attribution of record high daily temperatures in Australia in 2013 and 2014

There has been increasing scientific interest in understanding the climate factors associated with extreme weather and climate events. This has led to the series of special supplements in the Bulletin of the American Meteorological Society over the last three years on “Explaining Extreme Events from a Climate Perspective”. A wide range of extreme events has been considered in the studies included in these supplements, ranging from heavy rainfall and drought events to record hot and cold seasons. However, there have been no studies so far on the attribution of record high daily temperatures at single sites.

Here we present analysis of the contribution of human-caused climate change to the frequency of events such as the record high temperatures that occurred across Australia on 7 January 2013, in Sydney on 18 January 2013, and the record 5-day spell of maximum temperatures above 42C in January 2014 . The recently launched citizen science distributed computing project weather@home ANZ ( http://www.climateprediction.net/weatherathome/australia-new-zealand-heat-waves/ ) has generated very large ensembles of simulated regional daily weather data needed for the attribution of extreme events. By comparing the frequency of extreme daily temperatures in the model simulations for 2013 and 2014 and for a counter-factual world without any human influences on the regional climate, we assess the role of human influences on the likelihood of these cases of record high daily temperatures in Australia in 2013 and 2014.