I recently wrote about the tragic bushfires in Australia and how it seems to me that it is reasonable to ask if this would have happened without anthropogenic climate changes.
Real Climate has the details on this in their latest post: Bushfires and extreme heat in south-east Australia.
The post is by David Karoly, Professor of Meteorology at the University of Melbourne in Australia. He identifies four factors in the fire’s ferocity – maximum temperatures, relative humidity, wind speeds and the ongoing drought – and discusses the possible role of climate change in each of them. For three of the four, climate change is either likely a factor or consistent with the observations. Wind speeds were not exceptional or related.
He begins this way:
There has been very high global media coverage of this natural disaster and, of course, speculation on the possible role of climate change in these fires. So, did climate change cause these fires? The simple answer is “No!” Climate change did not start the fires.
and I suppose it is important to state that clearly and plainly right up front, because “caused by” (wrong) is easily conflated with “would not have happened without” (my opinion).
What we had in Australia at the onset of these fires was a convergence of many extreme, and some unprecedented, conditions. Record breaking highs (like 47.5oC in Laverton), an extreme heatwave (“unprecedented in 154 years of Melbourne observations”), record low relative humidity (5%), a 12 year long drought and a record dry start to the year all conspired to create a huge tinderbox of bush. Lightening and arsonists were the triggers.
One very interesting thing Karoly discusses in the article is the Forest Fire Danger Index (FFDI) designed to gauge the weather conditions associated with fire danger. The scale was adjusted so that the weather during the infamous Black Friday fires in 1939 would have had a rating of 100. Ratings above 50 are considered extreme. At a number of sites in Victoria, Australia on February 7, 2009, the FFDI reached “unprecedented levels, ranging from 120 to 190.”
His conclusion is:
While it is difficult to separate the influences of climate variability, climate change, and changes in fire management strategies on the observed increases in fire activity, it is clear that climate change is increasing the likelihood of environmental conditions associated with extreme fire danger in south-east Australia and a number of other parts of the world
The article generally supports what I said, despite a couple of scolding comments I received, that it is not at all indefensible to say that this event was outside the natural range. Because he is a responsible scientist, he couches his conclusions in caveats and qualification. But, as I am an irresponsible blogger, I get to call a spade a spade.
This event would not have happened without the impacts of anthropogenic global warming.