How extreme is our extreme weather?

There has been a deal of talk about ‘extreme weather’ in the mainstream media over the last year or two, and with unseasonable heat waves earlier this month followed quickly by snow in some parts I’ve no doubt there will be more. Indeed, the CSIRO put out a press release in August warning us that it was likely there would be more.

The problem with all that scary talk is that it is not always clear what anyone is talking about. ‘Extreme’ compared to when, or where? — is my usual response. I can remember snowflakes on a freezing Christmas Day in Armidale, and old-timers in Canberra will tell you it has happened there, too. As so often, it all depends on what you are measuring, and  how good the measurements are.

We have short memories, anyway, and we ought to rely not on personal memories or anecdote but on good data. Was the recent drought, the so-called Millennium Drought, the worst ever? In terms of what? Cost to farmers? Quantity of rainfall? River flows? Australian GDP? I think that trying to rank-order these events is misguided. We have had three great droughts in Eastern Australia in the time since my grandparents were born: in the early 20th century, in the 1940s and in the late 1990s and early 21st century. They all lasted several years, and they all had dreadful effects on people. The Bureau of Meteorology maintains rainfall data for the Murray/Darling river system, and you can see one aspect of the droughts, and the floods too, in these data.

Was the recent flood in Brisbane the worst ever? If you are measuring in terms of insurance pay-outs, then yes. But then property insurance was not a big deal in the 1890s. If you are measuring how high the river got to, the worst was the one in 1894. One reason we hear about extreme weather now, at least in my opinion, is that the scaremongers want to maintain apprehension in the public, and do their best to link ‘extreme weather’ with global warming.

The Inter-Governmental Panel on Climate Change has, rather unfortunately for the scaremongers, issued its own report earlier this year saying that there is no strong evidence to support such a link, but it did not bang the drum about it. It isn’t clear, in fact, that extreme weather is even increasing in frequency. We don’t have a comprehensive account for Australia, but in the USA there is a new study, by Professor Roger Pielke Jnr, on one aspect of extreme weather — tornadoes.

Tornadoes are storms which have a violently rotating column of air stretching from the cloud to the ground. Ever since I saw The Wizard of Oz they have terrified me, because of their  random movement and their sound, and they certainly terrify those who are in their path, who are mostly the Americans who live in a belt of countryside colloquially called ‘Tornado Alley’. In 2011 tornadoes killed more than 500 people, and caused more than $28 billion in property damage. So tornadoes and the damage they cause are certainly worth studying.

Roger Pielke Jnr started by ‘normalising’ the damage caused by these violent storms, that is, seeing what the damage would have cost in a common base year, with the social conditions that operated in it: ‘We normalise for changes in inflation and wealth at the national level, and changes in population, income and housing units at the county level.’ You have to do something like that, or your comparison of monetary costs will be meaningless.

What did he find? First, damage from tornadoes has decreased since 1950. He is careful to note that there must be uncertainty about whether or not a given tornado was recorded — but he can point to 56,457 tornadoes since 1950, of which 33,746 caused some recorded damage! He thinks it’s possible that the actual incidence of tornadoes has also declined, though the data don’t allow him to assert that strongly. Yes, that of 2011 was one of the three worst; the other two were half a century ago.

I doubt we have had anything like that number of high-powered storms in Australia, and the closest I’ve seen to a real tornado was a spectacular willy-willy that occurred on a a cloudless day in the bush, and lasted only a few minutes. Nonetheless, Roger Pielke Jnr’s careful study is a model for what we could do here — and he points out that we already normalise property damage from bushfires. If you’d like to read the article, I list his website in my blogroll. Just click on that, and explore.

My guess, from what I’ve read, is that we won’t find that the incidence of droughts and floods in Australia is increasing, and we have more than a century of good data to go on. Would somebody like to do the work?

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