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No increase in hot days at Bathurst

By Jennifer Marohasy - posted Monday, 28 October 2013

When a cause is incorrectly attributed to a misfortune, we forgo the opportunity to learn, we forgo the chance to plan so that we can avoid making the same mistakes into the future. In the wake of the February 2009 Victorian bushfires, a book by Roger Franklin,Inferno, The Day Victoria Burned, explains that we are losing ground when it comes to managing fire. This may have a lot to do with willfully ignoring the well-documented mistakes of the past, in favor of popular politics.

The cost of continuing to ignore the evidence is enormous, not just the loss of human life – 173 people died in Victoria on February 7, 2009 – but the bush could be so much healthier, and safer for native animals. Watercourses would be protected from erosion so common immediately after ferocious fires, and also from the regrowth that has significantly reduced water runoff into the Murray Darling.

Instead of implementing the well-documented solution of prescribed burning, as a community we are distracted with commentary about a ‘clear link’ between climate change and bushfires.  Such commentary often ends with the recommendation that we need to invest much more as a nation, not in prescribed burning, but in ‘climate change’.  This entire discussion is prefaced on an assumption that temperatures are actually increasing in Australia. The technical literature specifically claims that the impact of increasing carbon dioxide concentrations will be manifested through an increase in maximum temperatures.


This last week bushfires have been raging in the Blue Mountains. Just to the west of the Blue Mountains is the town of Bathurst. Bathurst has one of the longest temperature records of any locality in Australia, with daily maximum and minimum temperature measurements recorded at the jail from 1858, and from the agricultural research station since 1909.  This temperature record shows that contrary to popular perceptions, it has not been getting hotter at Bathurst.

If we consider the longest temperature record, which is the daily mean maximum temperatures for Bathurst jail from 1858 to 1983, the hottest day was January 12, 1878, see Chart 1. On that day, 135 years ago, a mean maximum temperature of 44.7 degree C was recorded.

There are no temperature recordings for the jail after 1983, but recording started at Bathurst airport in 1990. The airport data indicates that the hottest day during recent times was on February 15, 2004 with a mean maximum of 40.7 degree C, see Chart 2.

The Bureau of Meteorology uses the data as recorded at the Bathurst Agricultural Research Station since 1909 for its Acorn-Sat program. This is a program where data is ‘adjusted’ and ‘homogenized’ and then particular localities are chosen in the development of an average temperature for the entire Australian continent. Such an average value, while practically useless, has political interest, and is used, for example, to develop temperature trends for Intergovernmental Panel on Climate Change (IPCC) reports.

The adjusted and homogenized data for Bathurst indicates that the hottest days on record are January 11, 1939, followed by January 14, 1939 at 40.7 and 40.6 degree C, respectively. January 12, 2013 was also hot, with a mean maximum of 40.2 degree C recorded at the Research Station, see Chart 3.



In summary, even using the adjusted and official data for Bathurst, Chart 3, temperatures are not exceptionally or unusually hot now. If we consider the longer record and the ‘unadjusted’ data, it was much hotter in the late 1870s and then again in late 1930s than it is now, Charts 1 and 2.  This is consistent with what we know about natural climate cycles.

It is fashionable to make a link between global warming and the recent bushfires in the Blue Mountains. But such claims of a causal connection are not supported by the available evidence. In particular, if the technical literature specifically claims that the impact of increasing carbon dioxide concentrations will be manifested through an increase in maximum temperatures, but there has been no increase in the maximum temperature, then the theory, in the end, is nothing more than a myth.

Public policy is best based on evidence and logic, not popular politics, however emotionally engaging and personally compelling. Indeed, blaming the bushfires on global warming won’t save one home or one watercourse from catastrophe.

Bushfires cannot be entirely prevented, but periodic mild, patchy fires alleviate the build-up of heavy fuels, so that when a fire does start it is easier and safer to suppress and does less damage. A regime of prescribed burning also produces a healthier and more vigorous forest and is better for biodiversity.

PS. It has been suggested that writing articles like this, and presenting evidence by way of the above charts, is akin to pouring a single bottle of water on a fire dance of raging global warming alarmists. Perhaps, but help me increase the humidity a little, by sharing this article with your friends and colleagues… its not exactly patch burning but it can perhaps help reduce connectivity through sowing a little healthy scepticism.

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This article was first published on Myth and the Murray.

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About the Author

Jennifer Marohasy is a senior fellow with the Institute for Public Affairs.

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