Fires are raging across New South Wales, building on an already aggressive early start to the fire season. An obvious question looms: is this unprecedented and does this have the fingerprints of climate change? With the support of NASA funding, my lab at the University of Tasmania has been studying fire season starts across Australia with a view to settling these questions. Unfortunately, this work, spearhead by an extraordinary amount of number crunching by geospatial analyst Dr Grant Williamson, has drawn many blanks. It isn’t yet possible to clearly define the factors that trigger an early fire season, their duration and intensity. Why? A cluster of reasons. First, we do not have highly reliable fire records in the epoch before satellites (around 1980). Without place and time specific data it isn't possible to detect a slight shift in fire season, particularly to answer the question of climate change. Second, unlike in North America we cannot easily reconstruct fire activity using historical proxies, calibrated against the instrumental record of meteorological observations. In the western part of the United States the pine trees have superb tree rings enabling reconstructions of the year and geographic extent of both droughts and past fire activity. Australia’s gum trees are useless for such reconstructions, and in any case our climate is notorious fickle being driven by the ENSO system that gives us the El Nino and La Nina weather patterns, making us a "sunburnt country" with "droughts and flooding rains". In sum we have insufficient data, and the time depth of the high quality records is too shallow. Despite this we can use synthetic thinking to understanding fire activity and fire risk. An important model proposed by Ross Bradstock at Wollongong University is that fires are triggered when four climate switches are all "on":
- Having enough unburnt biomass or bushland to burn
- The fuel to be dry, ready to burn
- Hot, windy weather
- Ignitions are in the landscape to start and spread the fires.