“An exceptionally prolonged autumn warm spell,” is what the Bureau of Meteorology calls it in a Special Climate Statement released today on the extended warm spell in May 2014 that affected most of Australia. These special statements are reserved for weather/climate events which are unusual in the context of the climatology of the affected region. Their purpose, says the Bureau, is to document major events. In doing so, they serve as a historical record, inform the public on the broader historical and climatological context for events, and give easy access to data and information which is in high demand from the media and the public.
So what’s the data that made May special?
Maximum temperature anomalies (from 1961–1990 average) for period 8 to 26 May 2014.
And the broader historical and climatological context for these events? Nothing in this explanation, relegated to page nine just above the appendices, that should upset a global warming sceptical Prime Minister:
The warm spell has been driven by persistent blocking in the Tasman, resulting in northwesterly winds over the southeast of the continent. While all exceptional climate events are driven by antecedent and concurrent weather
conditions, long-term trends also very likely play a role when significant climatological records are broken.
Australian annually averaged temperature has warmed by 0.9 °C since 1910, and the month of May has warmed by a similar amount. The annual warming trend is consistent with that observed for the globe.
The current warm event is the latest in a sequence of prolonged or intense warm spells that have affected a large part of the continent roughly every six weeks since the end of 2012. This coincides with record-breaking or well-above-average temperatures that have persisted across Australia for the past 22 months. The 12 months ending January 2014, February 2014, March 2014, April 2014 and May 2014 have all been record-warm for Australia. The year-to-date (January to May) temperature anomaly for Australia at 31 May 2014 was +0.84 °C. This will mean that 2014 ranks in the top five warmest starts to a year on record behind 2005 (+1.17 °C), 1998 (+1.05 °C), 2013 (+1.04 °C) and 2007 (+0.96 °C).