In climate change science, detection is the demonstration that climate
has changed in some defined statistical sense. A change is detected
in observations if its likelihood of occurrence by random chance
due to internal, natural climate variability is small. Attribution
is the process of establishing the most likely causes for the detected
change with some defined level of confidence. Evidence of a human
influence on the global climate has accumulated steadily during the
past two decades, based on such detection and attribution studies.
This paper is a review of detection and attribution studies of Australian
climate trends. The major Australian climate trends observed over
the past 50 years or so are: Mean maximum (daytime) temperature has
increased over most of Australia, with cooling in the northwest (very
strong in summer) and along the south coast of Western Australia
(in most seasons). Mean minimum (night-time) temperature has increased
over nearly all of the country except for cooling in some parts in
the inland northwest (in all seasons except spring, although the
location of the cooling varies between seasons). Annual rainfall
has increased in the northwest (a summer phenomenon), decreased in
the southwest (a winter phenomenon) and along and inland from the
east coast (Queensland in summer; New South Wales in winter). Pan
evaporation has declined about three per cent since the mid-1970s.
Detection and attribution studies of Australian climate indicate
that: The widespread warming is very likely to be due to increased
greenhouse gas concentrations. The rainfall decrease in southwest
Western Australia is likely due to a combination of increased greenhouse
gas concentrations, natural climate variability and land-use change.
The increased summer rainfall in northwest Australia may be due to
increased aerosols resulting from human activity, especially in Asia.
The apparent decline in pan evaporation is mainly due to changes
in instrumental exposure. No study has attributed a cause to the
rainfall decrease along the east coast. The highest priority for
new detection and attribution studies would appear to be the decline
in east coast rainfall, because of the large population and high
economic value of this region, the dearth of relevant studies, and
the magnitude of the apparent change. A more comprehensive, Australia-wide,
formal detection and attribution study to determine bow firmly we
can conclude that human activity has affected Australian rainfall
in general, is also a high priority.
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