Following a brief reading of the World Weather Attribution report regarding the 2019 Australian bushfires, I felt the following extracts were worthy of comment:
“The study reveals the complexity of the 2019/20 bushfire event, with some, but not all drivers showing an imprint of anthropogenic climate change.”
That seems fair enough. But, of course, the press are only interested in those drivers that do show “an imprint of anthropogenic climate change”.
“In addition, ignition sources and type of vegetation as factors largely outside the meteorology play an important role. In this analysis we only consider the influence of weather and climate on the fire risk, excluding ignition sources.”
So they have conditioned their analysis with respect to “ignition sources and type of vegetation”. That’s one hell of a conditioning. It would have been nice to understand how the percentage risk changes when one conditions instead upon anthropogenic climate change and explores counterfactuals regarding ignition and combustion, e.g. forest management counterfactuals.
“Thus, while it is clear that climate change does play an important role in heat and fire weather risk overall, assessing the magnitude of this risk and the interplay with local factors has been difficult. Nevertheless it is crucial to prioritise adaptation and resilience measures to reduce the potential impacts of rising risks.”
Absolutely, it is crucial to prioritise. That is why it is so important to explore all factors, including the global and local, and the climatological and non-climatological.
“We therefore investigate the question how anthropogenic climate change influences the chances of an intense bushfire season, rather than focusing on a single episode of intense bushfires.”
That’s weird, because I got the distinct impression from the press that this report was all about a single episode of intense bushfires, i.e. Australia 2019. And for a report that didn’t focus on a single episode, it certainly had a lot to say about it! If the report wasn’t supposed to be about a single episode, perhaps the text ‘Australian Bushfire’ shouldn’t have appeared in its title.
“Attributing observed trends to anthropogenic climate change can only be done with physical climate models as they allow isolating different drivers.”
Further evidence here that the report is only interested in studying ‘observed trends to anthropogenic climate change’. Attributions for specific events can then made with little or no regard to local context, presumably.
“The attribution statements presented in this paper are for events defined as meeting or exceeding the threshold set by the 2019/20 fire season and thus assessing the overall effect of human-induced climate change on these kind of events. In individual years, however, large scale climate system drivers can have a higher influence on fire risk than the trend. Besides the influence of anthropogenic climate change, the particular 2019 event was made much more severe by a record excursion of the Indian Ocean Dipole and a very strong anomaly of the Southern Annular Mode, which together explain more than half of the amplitude of the meteorological drought (precipitation deficit). We did not find a connection of either mode to heat extremes.”
There you go! Buried deep in the report, an admission of the importance of the non-anthropogenic precipitation deficit, but no attempt to perform a counterfactual analysis that conditions upon the anthropogenic drivers so that the deficit’s impact in terms of percentage risk can be calculated. Could this be because no one was interested enough to do so, or was it because the factors were deemed too complicated? Either way, you will search in vain in the report for a statement along the lines of “A record excursion of the Indian Ocean Dipole and a very strong anomaly of the Southern Annular Mode increased the risk of the fire event by x percent.” All one can find is a strong hint that such a percentage would likely turn out to be a lot more impressive than the one attributed to anthropogenic climate change. As I have said before, when it comes to causal analysis, the storyline one creates depends largely upon the causal agents one conditions upon.
Caveat: I haven’t finished reading the report. I might yet change my position. There is also the possibility that someone like Jaime Jessop will upstage me by doing a lot more thorough job.