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> June
2005 was warmest year on record
AUSTRALIA has officially recorded its warmest year on record.
Data collected by the Bureau of Meteorology indicates 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 the country's 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 December 15, 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 south-east.
Preliminary data indicate that the average total rainfall throughout
Australia for 2005 was about 399mm, 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.
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