No statistically significant increasing trend in summer fire weather conditions over eastern NSW
H. Clarke et al.(2012) found NO statistically significant increase in summer Forest Fire Danger Index(FFDI) between 1973 and 2010 over eastern New South Wales over the region that has been experiencing unprecedented fires recently.
In fact there was even a slight decreasing trend in FFDI at some stations but it was not statistically significant.
This pattern may reflect more frequent positive Southern Annular Mode(SAM) decreasing fire danger but increasing temperatures increasing fire danger thus the cumulative effect is not statistically significant.
There is however, a statistically significant increasing trend over South Australia and northwestern Victoria. During spring, there is also a statistically significant increasing trend over parts of eastern New South Wales but that is likely associated with the extension of the length of the bushfire season towards earlier in spring as temperatures increase.
Images from study:
Map of trends in summer Forest Fire Danger Index(FFDI) between 1973 and 2010. Marker size is proportional to the magnitude of trend. Reference sizes are shown in the legend.Filled markers represent trends that are statistically significant. The marker for Laverton has been moved west to avoid overlap with Melbourne Airport:
In fact there was even a slight decreasing trend in FFDI at some stations but it was not statistically significant.
This pattern may reflect more frequent positive Southern Annular Mode(SAM) decreasing fire danger but increasing temperatures increasing fire danger thus the cumulative effect is not statistically significant.
There is however, a statistically significant increasing trend over South Australia and northwestern Victoria. During spring, there is also a statistically significant increasing trend over parts of eastern New South Wales but that is likely associated with the extension of the length of the bushfire season towards earlier in spring as temperatures increase.
Images from study:
Map of trends in summer Forest Fire Danger Index(FFDI) between 1973 and 2010. Marker size is proportional to the magnitude of trend. Reference sizes are shown in the legend.Filled markers represent trends that are statistically significant. The marker for Laverton has been moved west to avoid overlap with Melbourne Airport:
Table of trends in Forest Fire Danger Index(FFDI) between 1973 and 2010 by season and 50th percentile(median) and 90th percentile.Shading indicates trends are significant at the 95% level:
Table of trends in Forest Fire Danger Index(FFDI) between 1973 and 2010 by season and 50th percentile(median) and 90th percentile.Shading indicates trends are significant at the 95% level:
You can read the study at http://images.smh.com.au/file/2013/09/14/4747251/fires1973.pdf
And this lack of statistically significant increase in FFDI is despite 1973 being the base year when the 1970s was a wet decade over NSW and it was relatively dry from the 1900s Federation Drought to the 1940s World War II drought.
If the trend was from 1900 there could even be a statistically significant decreasing trend in FFDI over those parts of NSW but I don't have access to such data.
NSW/ACT rainfall time series showing that it was dry from the 1900s to 1940s but wet in the 1970s(from BOM):
And this lack of statistically significant increase in FFDI is despite 1973 being the base year when the 1970s was a wet decade over NSW and it was relatively dry from the 1900s Federation Drought to the 1940s World War II drought.
If the trend was from 1900 there could even be a statistically significant decreasing trend in FFDI over those parts of NSW but I don't have access to such data.
NSW/ACT rainfall time series showing that it was dry from the 1900s to 1940s but wet in the 1970s(from BOM):
Observations analysed in (Dowdy 2017) also show a similar pattern (no statistically significant increase in mean FFDI and frequency of severe FFDI in summer).
Screenshot from study.
This analysis shows that it would be wrong to assume without prior study and analysis that a single or every single extreme fire event was made worse by climate change just because statistically on average, fires are expected to become more frequent and more intense over many parts of the world. This is because any individual event occurs due to a unique set of circumstances which led to it and these circumstances may be affected by different ways by global warming.
Hope, P. et al., (2018), a study on record fire weather across central-eastern Australia in February 2017 did not find a clear signal as to the influence of increasing atmospheric CO2 on fire weather.
It would even be wrong to assume that all extreme heat events were made more likely or all extreme cold events were made less likely by climate change just because that is the projected global pattern.
For example, climate change could have made frost over Southwestern Australia more likely because of the drying trend as well as changes in atmospheric circulation, location and behaviour of high pressure systems and ridges.etc.
Nevertheless regardless of the influence of climate change on the bushfires in late spring and early summer recently, it is likely that fire conditions are expected to become more common and intense over large parts of Australia and the world as temperatures increase with parts of Southern Australia also drying with climate change.
Irrelevant of whether or not climate change were to blame for the bushfire crisis in New South Wales the case for sensible climate action is extremely strong and has been made long before this intense bushfire season
It would be missing the forests for the trees to use these bushfires as an argument for or against sensible climate action.
This analysis shows that it would be wrong to assume without prior study and analysis that a single or every single extreme fire event was made worse by climate change just because statistically on average, fires are expected to become more frequent and more intense over many parts of the world. This is because any individual event occurs due to a unique set of circumstances which led to it and these circumstances may be affected by different ways by global warming.
Hope, P. et al., (2018), a study on record fire weather across central-eastern Australia in February 2017 did not find a clear signal as to the influence of increasing atmospheric CO2 on fire weather.
It would even be wrong to assume that all extreme heat events were made more likely or all extreme cold events were made less likely by climate change just because that is the projected global pattern.
For example, climate change could have made frost over Southwestern Australia more likely because of the drying trend as well as changes in atmospheric circulation, location and behaviour of high pressure systems and ridges.etc.
Nevertheless regardless of the influence of climate change on the bushfires in late spring and early summer recently, it is likely that fire conditions are expected to become more common and intense over large parts of Australia and the world as temperatures increase with parts of Southern Australia also drying with climate change.
Irrelevant of whether or not climate change were to blame for the bushfire crisis in New South Wales the case for sensible climate action is extremely strong and has been made long before this intense bushfire season
It would be missing the forests for the trees to use these bushfires as an argument for or against sensible climate action.