26 September 2007

Bushfires and climate change in SE Australia

A bit of self-promotion...

The Climate Institute of Australia today released a report entitled “Bushfire Weather in Southeast Australia: Recent trends and projected climate change impacts”. I am proud to say that I am the lead author on the report. I will briefly summarize the results.

The basic idea of the study was 1.) to evaluate the potential changes to weather conducive to bushfires in 2020 and 2050 using two CSIRO climate models made for the IPCC 4th Assessment, and 2.) compare these changes predicted by the model to what has been observed to evaluate how well the model is doing.

The first part was fairly straightforward, and follows on from a similar study we did a couple of years ago using the IPCC 3rd Assessment. The results were also similar. Broadly speaking, we found a 10-30% increase in fire danger across southeast Australia (NSW, VIC, TAS,ACT, SA and southern QLD) for the worse case scenarios by 2050. This was accompanied by a doubling of high-risk 'extreme' days, where wildfires are generally uncontrollable. We also looked at some of the extreme upper ranges, where much of the house loss and other types of damage occur, finding a similar increase.

Pretty scary stuff, but wait for the other shoe to drop...

Looking at the observations revealed that over the past 5 fire seasons in southeast Australia, we have consistently exceeded the fire danger predictions the model made for 2050. In other words, we are already there! The 2006-7 fire season was, by many measures, the worse fire weather we have experienced in our records at many of the stations. The 2002-3 season was also quite bad (Canberra bushfires), but unlike previous times, there hasn't really been much of a break between these two extreme seasons, which is unprecedented. Our records are limited. For example, the few long time series we were able to gather only extend back to the 1940s, and so fail to encompass some historically bad events like the 1939 Black Friday bushfires in Victoria. There are, as always, a few issues with the data, but we have done our best to work around those and we openly acknowledge what and where the problems exist.

Now, of course we cannot absolutely attribute all of that change to climate change, and we were very careful in the report not to do so. We cannot rule out interdecadal variability, for example. We did detect apparent 20-year cycles in the weather data, and we are currently in an upswing (apparently) in recent years. But, the peaks we are seeing now are higher than those in the past. We hypothesized that what we are seeing is some combination of climate change and interdecadal variability. The test of our hypothesis comes in the next 5-10 years of observations. If natural variability is playing a large role, the we will see a decline in the upcoming years, with a retreat towards conditions more like the 2020 model projections. If we don't see this decrease, the conclusion must be that the climate models are too conservative in this instance, and we are underestimating the impacts of climate change.

This last point is akin to the recent situation with the polar ice caps, wherein the melting is proceeding at a much faster pace than what was previously predicted. We don't have a complete understanding of the climate system (nor does anyone claim we do) and the models may be wrong. Unfortunately, not wrong in our favor. It all points to the fact that the time to act on mitigation of and adaptation to climate change is now (which is the point the Climate Institute is making with our report).

With this report, we have hit the major media outlets in Australia. We were the lead story on the 7:30 Report, a national news magazine. Transcripts and videos here (your humble blog author is featured in these interviews). I saw the report this evening, and I feel they did a pretty good job of reflecting the uncertainties and not exaggerating too much. We have also stories in most of the major newspapers in Australia. Will try to update with links to a few of these stories in the near future...

For those interested in the progress of this year's bushfire season in Australia, I encourage you to visit my other blog, the Australia Bushfire Monitor. There, I keep tabs on the major bushfire developments and events as they occur throughout the country.

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