Graph 1
© By Peter Burr, 15 June
2007
No part of the following may be reproduced for commercial purposes without prior
permission from the author.
There is no doubt that the climate is warming. Statistics show that over the last 50 years temperatures in Australia have been rising steadily. Whether this event is part of a natural warming cycle, or whether it has been brought on by human activities, remains to be accurately determined. It may well be a combination of both. The University of New England/Bureau of Meteorology weather station in East Armidale which has been in operation since 1981 shows some interesting trends over the last 26 years.
Maximum or daytime temperatures have shown a marked rising trend from an average of 19.0 degrees in the early 1980s to 20.4 degrees in 2006, an increase of 1.4 degrees (see Graph 1). The average annual number of hot summer days reaching 30 degrees or higher is also sharply on the rise with an increase from 9 days in the early 1980s to 17 days in 2006 (see Graph 3). Balancing this, cold winter days are showing a distinct decreasing trend. In the early 1980s Armidale was averaging 22 days per year with maximum temperatures below 10 degrees. By 2006 this had dropped to just 8 days (see Graph 4).
Minimum or overnight temperatures, however, are not on the increase as one would expect with a warming climate, but have been slowly decreasing over the 26 year period from a yearly average of 6.2 degrees to 5.9 degrees (see Graph 2). A possible reason for this could be an increase in cloud-free nights in more recent years. Overnight temperatures usually drop lower on clear nights than cloudy nights. This would also explain why the annual number of frosts has been gradually rising from an average of 92 in the early 1980’s to 105 in 2006.
Annual
rainfall totals have shown no noticeable increase or decrease since 1980 and
therefore are unlikely to have contributed to the warming temperature trends.
The UNE
weather station also measures daily pan evaporation which is directly affected
by temperature, humidity, wind and sunshine. Readings commenced in 1983, and
over the following 24 years there has been a slight increase in yearly
evaporation from an average of 1200 mm at the beginning of the period to 1240 mm
at the end of 2005. This rise is not large enough to be significant, but with
overall temperatures increasing it would be expected that evaporation would also
increase.
The figures
and trends discussed here have covered the last 25 years since the UNE weather
station has been in operation, but what of the longer term?
Although temperature recordings commenced at the post office in 1858, some
rather suspect extremes turned up in the first 30 years of these records, also
there were many gaps. More reliable continuous records appeared from 1891
onwards which show some interesting trends over the last 116 years. There was a
cool period from 1891 to 1935, then a general warming in the second half of the
thirties and throughout the forties and fifties. Another cooler period followed
in the sixties and seventies followed by the present warm period. The hottest
year was 1998 and the coolest was 1891. The Bureau of Meteorology which uses a
database from selected weather stations across Australia from 1910 onwards has
recorded 2005 as Australia’s hottest year. Over the 25 year period from 1981 it
was Armidale’s second hottest after 1998.
Climatologists predict that continued warming is highly likely, both in
Australia and globally. The next few years of data recorded in Armidale should
produce very interesting results. Will rainfall increase or decrease? Will
maximum temperatures continue to rise at the present rate, and will minimum
temperatures also commence to rise? A least a further five years of data will be
required to answer these questions.
Graph 1
Graph 2
Graph 3
Graph 4
Graph 5
