On Thursday the New South Wales Government officially declared the nine-year drought ended. The very next day the CSIRO released a report warning that the ‘current drought’ appears to be at least partly linked to ‘climate change’.
The CSIRO report entitled ‘Climate variability and change in south-eastern Australia’ is an initiative of the South Eastern Australian Climate Initiative, SEACI, lead by CSIRO with input from the Bureau of Meteorology and the Murray-Darling Basin Authority.
The report forecasts a future decline in rainfall and works from the assumption there is already long term decline.
The first diagram, Figure 1, however, only shows historical rainfall data for the period 1997 to 2009 excluding the last very wet ten months. The first graph, Figure 2, shows inflows, not rainfall, across the Murray Darling Basin without explaining that many variables impact inflows that have nothing to do with rainfall including changes in land management, salt interception and drainage schemes etcetera.
A scientific report of this kind might have begun with a discussion of the complete historical rainfall record and avoided confusing inflows with actual rainfall.
The report’s forecast of a drier future could come to pass, but the track record of Australian climate scientists for predicting rainfall even one season ahead is dismal. The Bureau incorrectly forecast below average rainfall for spring this year for the upper Murray catchments just before the region was flooded. Last year the forecast for a hot and dry summer resulted in drought breaking rains across the upper Murray Darling Basin.
Rainfall – the most significant climate variable – is spectacularly changeable and non-robust from one climate model to the next.
Professor Gareth Paltridge in his book ‘The Climate Caper’ (Connor Court, 2009, pg 21) makes reference to an Australian National University study of the various simulations of rainfall as produced by the IPCC models. The simulations of average Australian rainfall apparently range from less than 200mm per year to greater than 1000mm per year. The actual measured value is 450mm. Considering the forecasts for the late 21st Century, apparently more than half the models predict an increase in rainfall over Australia, and the rest predict a decrease. The most extreme decrease is from the CSIRO IPCC model which suggests that average rainfall over Australia 100 years from now will be 100mm per year less.
At the global scale, according to AGW theory, an increase in carbon dioxide should lead to an increase in water vapour concentrations and therefore more cloud. But there is some empirical evidence to suggest that water vapour feedback is in fact negative, not positive.
In summary, there is no reason to suggest that the new SEACI forecast for a decline in rainfall across south eastern Australia will be any more accurate that previous CSIRO and Bureau of Meteorology seasonal and long range forecasts that have proven unreliable. Furthermore it is of concern that the report purportedly about south eastern Australia, released in October 2010, makes continual reference to the ‘ongoing drought’ and ‘current drought’ when south eastern Australia is no longer in drought.