Don't wave goodbye just yet.

In the days leading up to the time when I sat down to write this, news outlets have been full of stories and images of the destruction and loss of life cause by a tsunami which struck parts of Indonesia. Just prior, however, the same media outlets had been giving publicity to a prediction that Sydney would be wiped out by a tsunami on September 20th. I was able to joke about this by saying that as I live 1100 metres above sea level I wouldn't be directly affected but it might spoil the party for my birthday two days later when my friends and relatives were washed out to sea.

For many people though it might not have been a joking matter. The fact that some television shows which purport to cover news had covered the story could have given it credibility, and had the Indonesian disaster happened a few days earlier it would have been easier to imagine the damage to Sydney of a huge wave rushing up the harbour and across the beaches.

Apocalyptic predictions have been around for a very long time, and inductive reasoning would suggest that it is a safe bet to assume that things that have never happened will continue to not happen, just as things that always happen can be assumed to keep happening. (Yes, I am aware of Hume's criticism of inductive reasoning, as are all those people who thought that the managers of their superannuation funds would continue to back winners in the stock exchange.)

Maybe formal logic isn't required here, just an application of some simple critical thinking. How could a tsunami be so focussed that it would only affect Sydney and not Newcastle and Wollongong? What geological event could trigger it? (The North Island of New Zealand collapsing into the ocean would do it, but that would certainly affect more of the Australian coast than Bondi and in any case would have been even more predictable if predictions of disaster were reliable.)

This sort of prediction usually arises from someone misreading or misunderstanding  some religious text, but if God had wanted to punish Sydney why on that date and why use total destruction? If he objected to the Gay and Lesbian Mardi Gras why wait until September rather than blitzing the place in March? If the problem was excessive gambling, why not just symbolic lightning strikes on the casinos and Randwick Racecourse? After all, God promised in Genesis 9 not to use a flood as a means of destroying everything ever again, although strictly speaking Sydney is not all the world despite what its residents might think.

So, what's the real harm in these predictions?

There are two harmful effects. The first is that people might believe that what is predicted might actually come to pass. When the world was gripped by predictions of the end of times a few years ago, NASA, for example, had to divert resources from its real business to explaining why the earth can't instantaneously reverse its direction of spin, why the magnetic poles cant flip at a moment's notice and why there can't be a massive planet moving through the solar system without being detected. On a more serious matter, people sold or gave away all their possessions and in some parts of the world there were large numbers of suicides when the predictions didn't come true.

There is also the danger that people apply the induction I mentioned above and think that because these predictions were vacuous that all predictions can be ignored. In the middle of a drought Sydney's water consumption has increased because the city has never actually run out of water. Some residents of the Blue Mountains aren't prepared for bushfires because there isn't a big fire every time the Rural Fire Service issues a total fire ban. People drive while drugged or drunk because they have done it before without any problem.

A little critical thinking can go a long way.

To end on a lighter note, here is something to remember for trivia night at your local pub. The English language has unashamedly borrowed words from other languages  when those words express ideas which take a lot of words to say in English. Think schadenfreude from German, trio from Italian or algebra from Arabic. When I was young big destructive waves were called "tidal waves" but as they had nothing to do with tides a better word was needed for big waves caused by geophysical events so "tsunami" entered English from Japanese. Here's where the trivia part comes in. The initial phoneme (the first sound) in the Japanese pronunciation of the word does not occur in any dialect of English, so when we use a word that we all understand we mispronounce it because we really have no choice. I always knew the linguistics I studied at university would come in handy one day.

This article was published as the Naked Skeptic column in the November/December 2018 edition of Australasian Science