Roger’s blog post yesterday on Australian Bushfire Damage and Climate Change is a bit of a giveaway as to where my main interest lies in the report, the section on ‘Extreme events’. In this post, I will focus only on the sub-section dedicated to ‘Bushfire intensity and frequency’.
My main issue is the report’s use of a key reference, the study by Cai et al. (2009c, full citation below) entitled “Positive Indian Ocean dipole events precondition southeast Australia bushfires”, to support the statement that
“the intensity and seasonality of large bushfires in southeast Australia appears to be changing, with climate change a possible contributing factor”While I have no issue with the Cai et al. study itself (we cited this in our recent bushfire paper), at best, the use of it in the Commission’s report is clumsy, and at worst, misleading.
The first thing that has been lost in translation (some may argue I am splitting hairs here) is while the Cai et al. paper has the words ‘southeast Australia bushfires’ in its title, it is actually focused exclusively on Victorian bushfires. Thus, it does not fully support the statement above, nor does it discuss the 2003 Canberra bushfires.
More important is that the definition used in Cai et al. to categorise historical Victorian bushfire seasons (1950-2009) as ‘significant’ incorporates historical impacts (fatalities, property, livestock losses) rather than meteorological variables. If the purpose of the bushfire sub-section of the Commission’s report is to discuss the bushfire hazard, which I believe to be the case based on my reading of other Extreme events sub-sections, then it makes no sense to refer to a paper that incorporates impacts.
In other words, it is nonsensical to report on possible changes in bushfire hazard intensity using a measure of bushfire intensity that incorporates impacts.
If instead the statement in the report was referring to impacts, then why was the conclusion from our research not cited here – that there is no discernable evidence that the normalized Australian bushfire building damage (1925-2009) is being influenced by climate change due to the emission of greenhouse gases (PDF)?
While it may not materially change the results of Cai et al., it is also worth mentioning that the impacts used to classify historically significant Victorian summer bushfire seasons were not normalized.
Lastly, the Cai et al. conclusions relating to climate change focus on the possibility of bushfire risk increasing in the future and do not relate to the influence climate change has had to date.
In sum, as far as the bushfire sub-section of the Climate Commission’s report is concerned, it seems that both accuracy and clarity have been sacrificed for economy. And that, unfortunately, will always do far more harm than good.
References
Cai, W., T. Cowan, and M. Raupach, 2009c: Positive Indian Ocean dipole events precondition southeast Australia bushfires. Geophys. Res. Lett., 36, L19710, doi:10.1029/2009GL039902.
Crompton, R. P., K. J. McAneney, K. Chen, R. A. Pielke Jr., and K. Haynes, 2010. Influence of Location, Population and Climate on Building Damage and Fatalities due to Australian Bushfire: 1925-2009. Weather, Climate, and Society, 2:300-310.