Strange Weather We're Having

We’ve just experienced two weeks of rain, drizzle, solid cloud, and thunderstorms in Johannesburg, and it’s raining right now.  I’m sure that this is not provoking any sympathy from people enjoying winter in the UK or the US.  But this is summer here!  Johannesburg’s normal summer weather involves rain – it’s our rainy season – but summer rain here means a thunderstorm rolls in late afternoon, gives us a good drench, and then rolls out again and the sun comes out.  Back to the swimming pool.  So a solid two weeks of European winter weather – in March – is extraordinary.  And that started me thinking about what I actually meant by that statement.

In the first place, we had a patch of weather like this last year – not as long or depressing, but the same sort of thing.  That was in winter which is usually our dry season here.  Rather more to the point, what sense does it make for me to talk about weather in Johannesburg being “unusual” on the basis of the time I’ve lived here?  Sure, I’ve been here for forty years, but the planet has been around for billions of years.  So what I really mean is that the weather has apparently changed from what has been normal over the last short time period.  Make that very short.

The recent climatic behavior has also provided a boost for the climate change naysayers.  “Global warming?  What nonsense!” we hear.  “Why I remember…”  Okay, so in the first place we’re back to the last twenty years or so that they remember.  In the second place there’s a reason that climatologists want it called climate change and not global warming.  Yes, the carbon dioxide increase will provide an overall increase in the earth’s temperature in the long run, but the effect might be a change in the jet stream southwards.  If that happens, northern Europe will enjoy another ice age…as a result of global warming.  This sort of comment usually leads to understandable frustration and disgusted cries of, “Well, can’t you people make up your minds and tell us then?  You claim to be the experts!”

Well, no.  I believe that the experts can’t tell us.  One of my applied mathematics colleagues at Wits University developed the idea of frame-based models for ecological systems.  The idea was that in an ecological system, there are regions of stability.  You have enough rainfall for the vegetation so that the herbivores have enough food so that the predators have more or less enough to eat and use behavioral constraints to control their population.  Then something big happens – prolonged drought, disease, whatever.  The system changes quite quickly to another situation and settles down there after a comparatively short time.  These relatively stable situations are the frames.  Between the frames anything goes.

In fact this is a local way of looking at the full behavior of these types of systems.  Highly complex dynamical systems – like weather – have regions of stability and regions of high instability.  Moving a little away from the stable region may take you somewhere completely different.  These types of systems produce very beautiful pictures of how a point would move around under the constraints of the system.  And the stable regions can look quite unstable in their way.  These are sometimes called strange attractors and are at the heart of such chaotic dynamical systems.

So I think we’ve started moving between climate frames.  And that means that right now anything goes.  The weather may get hotter or cooler or wetter or dryer, and that may change from year to year.  Could be an interesting ride.

Oh, by the way, these chaotic systems were discovered by a scientist by the name of Edward Lorentz in the early sixties.  He was trying to do weather prediction at the time…

Michael – Thursday.