Bushfires

I have recently returned from a few weeks in Tasmania. Before I write up some trips there, I need to comment about the bushfires.

I spent my childhood in the Blue Mountains, so grew up familiar with bushfires. One summer a fire burnt out the gully behind our house. Another time, a very large fire had been burning way out in the Grose Valley but was slowly getting closer. It eventually approached the street where we lived – and was successfully fought and no houses were lost. Then a day or two later things changed. I can remember being at school, and the day finished early with a special assembly. Our headmaster advised us that the bushfire had suddenly become much worse. It had jumped the railway line and in one day had burnt out a huge area. A lot of houses had been burnt down, and consequently, students living in some towns would not be going home. Instead, their school bus would take them to the local civic centre which would provide emergency accomodation. Quite a number of students at the school found their homes had been burnt.

A few years later, when I had started bushwalking, I gained an appreciation of the extent of the Greater Blue Mountains. Local wisdom was that there was a bad bushfire every ten years or so. These fires would usually start from lightning strikes and then spread slowly, burn out an area, then stop when enough rain fell or they reached a natural boundary. Much has changed since.

The bushfires of 2019-20 started after a very long period of severe drought. I have been familiar with bad drought periods before – eg in the early 80’s and early 90’s, when rivers such as the Kowmung stopped flowing and became a series of pools. However the present drought, seems to me, much worse. I have never seen the bush in the Blue Mountains so dry. I have never seen the forest floor in areas of rainforest so dry with a carpet of leaves that crunch when you walk over them. I have never seen creeks downstream of hanging swamps dry up so severely. Hanging swamps act as a sponge and absorb rainwater and then slowly release it and usually ensure the downstream creek remains flowing. Now, the plants that make up those swamps are either dying because of the drought, or have been burnt out by fires.

The drought has been the reason the present fires have been so extensive. Nearly the whole Greater Blue Mountains have been burnt out – Kanangra Walls, The Kowmung River, The Blue Breaks, Jamison Valley, The Grose Valley and all the Northern Blue Mountains. In my experience, this has never happened before. Many of the burnt areas had been subject to hazard reduction burns in periods not long before the fire. This seems to have had little impact on the spread of the fire, although it may have reduced the fire’s impacts close to dwellings. It seems that most of the recent bushfires were started by lightning strikes. With very hot conditions, low humidity and strong winds, the fires can create their own weather. The burning vegetation sucks in air needed for  combustion. This can result in a positive feedback loop – the sucked in air creates more wind which makes the fire burn hotter. The heat can then ignite the vapour escaping from Eucalypt leaves causing the crown of the forest to burn at a very high intensity. More air is sucked in. This is a fire storm and is impossible to fight by firefighters.

What caused the fires? Arson? No. Ignition seems to have been due to lighting strikes, caused by thunderstorms without much rain. The drought has made the bush so much drier and prone to burning. What caused the drought? It is probably reasonable to attribute it to be largely due to climate change. But we have always had droughts? Yes, but… . Worldwide, the occurrences of severe weather including bad droughts in other places are far ahead of the normal statistical fluctuations you would expect. Several standard deviations in excess of what you would normally expect.

I can remember, former Prime Minister Tony Abbott making the comment –

At the time (2013), I can remember turning this quote into a timeline to show my students (I was then teaching high school science) how useful these graphs can be. This is how the quote now appears –

I think it easier with the timeline to see a worrying trend. It is also worrying to see senior politicians with no science training or immune from scientific advice.

I felt sorry for another politician a few days ago, when I heard her proclaim that how could the climate models be correct when they can’t even accurately predict the weather next week. Sad to see a politician so ignorant and limited.

The climate change models have proved to be  quite accurate is their predictions of key consequences of our increasing the carbon dioxide in the atmosphere. The models can’t predict things such as a bad Australian drought in 2017 – 19, but they do predict that such abnormal climate events are more likely. And that has been the case worldwide. More severe storms, more severe floods, more severe droughts.

Even more worrying is that the Earth’s climate may be approaching tipping points. Once these have been reached then the consequences are irreversible even if the amount of atmospheric carbon dioxide is later reduced.

For me – much of my bushwalking and canyoning is now on hold. For many others, things are a lot more serious – lives have been lost, people’s houses burnt down, livelihoods affected. Not good. And even more serious for countless animals and plants. It is likely that whole species have been wiped out.