At last there has been some rain across the NSW grain belt. But what is the longer term forecast?
On the 23rd June on ABC Television's 7.30 Report, Dr Tim Flannery, a member of the Wentworth Group of environmental scientists, predicted global warming is going to "affect Australia sooner and harder than anywhere else on the planet". The impression was that we might be going to enter an "eternal drought".
Dr Flannery went on to suggest Perth may soon become a "ghost metropolis" as a consequence of water shortages induced by global warming.
My colleague, Professor Bob Carter, recently had a paper published in the influential American journal Science (Vol 304, pg 1659).
Professor Carter is a geologist who has been involved in the international ocean drilling program for many years. In the paper he interprets the climate record for the last 4 million years from a sediment core taken off the coast of New Zealand.
Four million years is a long time!
Carter's interpretation of the data, and the cycles evident in his sediment core, fit closely with what are known as the Milankovitch Cycles.
These cycles last about 20,000, 40,000 and 100,000 years, and reflect changes in the tilt of the earth's axis and the eccentricity of its orbit as it circumnavigates the sun.
These cycles, along with significant events on earth, including volcanic activity associated with the pulling apart and stitching together of continents, have been used to explain past ice ages.
At the moment we are enjoying an inter-glacial warm period.
Looking at the cycles in Professor Carter's paper it would be reasonable to conclude that we will enter another ice age sometime soon -- in the next few hundred or so years.
While atmospheric carbon dioxide levels are currently rising, associated with fossil fuels burning, it is worth noting that it is generally accepted that carbon dioxide levels 500 million years ago were approximately 20 times higher than they are today.
Dr Flannery's comments on television were really a gross exaggeration of results from CSIRO Atmospheric Research climate modelling based on scenario modeling developed by the Intergovernmental Panel on Climate Change (IPCC).
However, the IPCC takes the view that "a coherent picture of regional climate change via available regionalisation techniques cannot yet be drawn". CSIRO Atmospheric Research also acknowledges this, especially when predicting rainfall.
The Internet publication Coolwire has compared the Australian Bureau of Meteorology (BoM) three monthly rolling "Outlook" predictions for rainfall with the real world results.
Coolwire finds that even on a short three-month scale, the BoM modellers have problems getting the outlook to resemble the observation.
What reliability, then, for computer models which attempt to predict the whole planetary climate 100 years ahead?
Interestingly, on the same day that Flannery was telling Australia that Perth was in trouble, the city's dams were filling earlier than they have in the previous 4 years.
A couple of weeks later the Western Australian wheat belt was given a good soaking, raising the prospects of an above average season.
The only constant in the natural world is change. So, one other thing that you can be quite sure about is that if you haven't had rain yet, the drought will break for you one day.
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