A jest that passes around the sceptical fraternity has it that when we have hot days, or a hot spell, that’s global warming, and it’s an example of ‘climate change’. If we have an unexpectedly cool spell, on the other hand, that’s just ‘weather’, and what you’d expect — natural variability of some kind, no need to explain it, move on, nothing new here. Another quip has it that ‘climate’ is the average of ‘weather’. A third, from Melbourne, says that if you don’t like the weather, just wait a while, because it’ll change later in the day.
There is of course some truth in all of those little summaries. Climate is indeed defined generally as the average of weather. My Shorter Oxford gives the primary meaning of the word ‘weather’ as ‘The condition of the atmosphere (at a given place and time) with respect to heat and cold, presence or absence of rain etc.’ That’s pretty straightforward. The word comes from a long, long way back in the history of language, and the root is the Indo-European verb to ‘blow’: if you articulate the beginning of the word weather, you’ll see that you do indeed blow the sound out. The entries for the word both as a noun and as a verb take up more than a column of tiny print, so you can see it is an important word in our language.
Now buildings and other things ‘weather’, which means that they change over time, and also survive storms and other aspects of weather, which leads us at once to ‘climate’, which is a much more recent word, Greek in origin (the root is the verb to’ slope’). Its meanings point to places with characteristic weather (‘climes’), and to the prevailing weather there (what we have in mind when we speak of ‘hot countries’). The words ‘climatography’ and ‘climatology’ are coinages of the middle of the 19th century. The dictionary doesn’t mention ‘climate science’.
The climates of Singapore and Sydney are rather different, though each of them can have similar weather from time to time, and we all understand that. I mention all this fascinating historical stuff partly because I’m interested in it, and partly because it emerged a day or so in testimony given to a House Committee on the Environment in Washington given by an academic who was once the US Navy’s Oceanographer and senior climate person. His name is David Titley, and this is what he said, in part:
I am frequently asked if a specific or extreme event (for example, typhoon Sandy, drought, snowstorm) is or is not “caused” by climate change. Frankly, that is the wrong question. It’s like asking someone if their childhood upbringing “caused” him or her to attend a specific college. It’s more useful to think of climate as the deck of cards from which our daily, specific weather events are dealt. And as the climate changes, so does our deck of cards. For every degree of warming, we add an extra Ace into the deck. So, over time, the unusual hands, like a Full House with Aces high, become more plausible – and more common – with time.
It’s the deck of cards analogy that caught my eye. It sounds plausible, but then — isn’t it the opposite of the conventional view that climate is the average of weather? In that case the deck of climate cards is created by weather, and only those cards can be played, as it were. For example, Canberra where I live has never had a temperature of minus 40 degrees Celsius, so that card could not be part of the climate deck. But Canada’s capital city Ottawa certainly has had minus 40 degrees in winter, so that temperature is part of its climate deck. The more I thought about it, the more I thought that this senior climate person did not seem to be at the sharp end of his ship.
As I see it, weather, our daily fare, is what defines climate, not the other way around. And Dr Titley’s climate deck of cards is a fundamentally flawed concept. We don’t in fact add an Ace into the deck for every extra degree of warming. We mightn’t be having an extra degree of warming where we are. What if we were to have a degree of cooling? What then happens to the deck of cards? Altogether, I was disappointed in the way he gave his evidence. He used a quip that I have seen before, to the effect that ‘absence of evidence is not evidence of absence’, and while this sounds portentous (and precautionary) it is not, if you look at it closely. The fact that there is no evidence that little green men have secretly been bottling atmospheric carbon dioxide and transport it to Mars does not mean that they haven’t been doing so.
Much better and more factual evidence was given by two luminaries in the data-analysis world of climate, Dr John Christy and Dr Roger Pielke Jnr, and you can read summaries of what they said in Judith Curry’s recent Climate etc post, which also has links to the full testimony in each case.
Why bother with what is said in Washington? First, global warming is global by definition, so what people say elsewhere has relevance to us. Second, we have no equivalents much in Australia of these Congressional appearances, so they are valuable in their own right.[Update: I came across another jest, this time from Mark Twain. ‘Climate is what we expect. Weather is what we get.’]