Geoscience Reference
In-Depth Information
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there is only low confidence that human influences have contributed to
changes in tropical cyclone activity.
Historical changes in Australian weather extremes
Extreme temperatures
Among the most statistically robust observations of changes to Australian
climate have been changes in maximum and minimum temperatures. Most of
the observed trend in temperatures has occurred since 1950, with both maximum
and minimum temperatures increasing by around 0.9°C (Fawcett et al., 2012).
Over the entire twentieth century, the increase in minimum temperatures has
exceeded that of maximum temperatures by 0.35°C. Australia's warmest year was
in 2005. The ten warmest years occurred after 1980, with six of those ten years
occurring after 1998.
This has been accompanied by a shift in both warm and cool temperature
extremes. Averaged over the entire continent, the frequency of extreme high
temperatures, in both daytime maximum and night time minimum temperatures,
has increased while the frequency of extreme low temperatures has decreased.
The frequency of days with maximum temperatures above the 90th percentile,
after remaining fairly stable until about 1980, has increased by about 40 per cent
in the last three decades, while the frequency of minimum temperatures below
the 10th percentile has declined steadily after 1950, and is now about 40 per cent
below pre-1950 averages (Trewin and Smalley, 2013).
Across Australia, there has been a slight increase in the duration of heatwaves
(defined as consecutive days above the 90th percentile of daily maximum
temperature) since the 1950s (Alexander and Arblaster, 2009). There have,
however, been marked regional variations in the occurrence of multi-day
heatwaves over that time, with decreases in parts of southern coastal Australia
(especially south-western Western Australia), and strong increases further north
(Trewin and Smalley, 2013). The decreases in southern coastal Australia contrast
with increases in the frequency of single-day high temperature extremes at many
of the same locations over the same period.
Figure 3.1
shows the increase in Australian annual mean temperature since
1910.
Figure 3.2
shows the frequency of record high (black) and record low
(grey) maximum temperatures from station data for 1910-2011.
Figure 3.3
shows
the frequency of record high (black) and record low (grey) minimum tempera-
tures from station data for 1910-2011.
While warming trends in mean temperature are well established over the
second half of the twentieth century, it was not until after 1990 that strong
trends emerged in the frequency of record high maxima and minima, with
particularly large numbers in the decade from 2001 onwards. Over the 2001-11
period record high maxima outnumbered record low maxima by a ratio of 2.8 to
1, while for minimum temperatures the ratio was 5.2 to 1 (Trewin and Smalley,
2013).
