Issued 4^th January 2006

Australia's hottest year on record

Australia has officially recorded its warmest year on record. Data collected by the Bureau of Meteorology indicate that the nation’s annual mean temperature for 2005 was 1.09°C above the standard 1961-90 average, making it the warmest year since reliable, widespread temperature observations became available in 1910. The previous record of +0.84°C was set in 1998. While these temperature departures may seem relatively small, a 1°C increase in mean temperatures is equivalent to many southern Australian towns shifting northward by about 100km.

A record mean temperature was set because both daytime and night-time temperatures were high: the annual mean maximum temperature was 1.21°C above average (equal highest), while the mean minimum temperature was 0.97°C above average (2nd highest). Temperature anomalies varied throughout the year but autumn 2005 was particularly warm. April had the largest Australian mean monthly temperature anomaly ever recorded, with a monthly anomaly of +2.58°C breaking the previous record of +2.32°C set in June 1996.

Despite some regional variations, the warm conditions in 2005 were remarkably widespread. All States and Territories, apart from Victoria and Tasmania, recorded 2005 mean temperatures amongst their top two warmest years on record. The only region recording a cooler than normal year was a coastal strip of Western Australia extending from Cape Leeuwin to Carnarvon.

Many of Australia’s warmest years on record (such as 1988, 1998 and 2002) had temperatures boosted by significant El Niño events. However, no such event occurred in 2005, making the record warmth even more unusual. The 2005 record is yet another sign that our climate is changing. Since 1979, all but four years have been warmer than average in Australia.

Australian temperatures have increased by approximately 0.9ºC since 1910, consistent with global warming trends. Scientific studies have linked global and Australian temperature increases to the enhanced greenhouse effect. Whilst this warming trend is expected to continue into the decades ahead, annual temperatures are influenced by numerous factors, including natural variability, so 2006 will not necessarily be warmer than 2005.

Australian mean temperatures are calculated from a country-wide network of about 100 high-quality, mostly rural, observing stations. The Bureau of Meteorology Research Centre and National Climate Centre have undertaken extensive quality checking to ensure that the temperature records from these sites have not been compromised by changes in site location, exposure or instrumentation over time.

Warmer-than-normal temperatures were not confined to Australia in 2005, with many other regions reporting an exceptionally warm year. According to a preliminary estimate released by the World Meteorological Organization (WMO) on 15 December 2005, the global mean temperature for 2005 was about 0.48°C above normal, putting 2005 amongst the four warmest years globally since records commenced in 1861.

In addition to being warm, the early months of 2005 were also very dry over much of Australia. The January-May period was the 2nd driest on record. From June onwards rainfall reverted to near- to above-normal levels over much of Australia, but the lack of sustained above-normal rainfall led to the continuation of multi-year droughts in parts of Australia, particularly in the southeast.

Preliminary data indicate that the average total rainfall throughout Australia for 2005 was about 399 mm, compared with a long-term average of 472mm. Most regions recorded slightly-below or near-normal rainfall for the year.

Australia’s area-averaged rainfall is calculated from a network of around 5000 rainfall stations, most of which are staffed by volunteer observers. Observations from this network reveal that, when compared to their historical records, Tasmania was the wettest State in 2005, while Queensland and Western Australia were the driest.