The strange truth about El Nino

Illustration of changes in the height of the sea surface during an El Nino Event. It's hard to know exatly what to make of this graphic, but it does look nice. Courtesy of the BBC

Satellite data showing changes in the height of the sea surface. The large straight red band just to the left (West) of South America represents a region of warmer water which has expanded and caused an increase in the height of the sea surface. This picture was stolen from the BBC web site.

You will probably hearing a lot about El Niño this year because the Australian Bureau of Meteorology have predicted that El Niño conditions will build through the coming year.

The news stories will all look like something like this:

  • Yada Yada Yada
  • Drought/Flood somewhere because of El Niño and Climate Change.
  • Isn’t it terrible

There will be nothing you can do except to experience a sense of vulnerability. And if you are of a similar disposition to me, you may also experience an increased sense of general anxiety.

However the amazing fact, which I have never seen mentioned in all my years of reading about this stuff is that, collectively, we have no idea what causes El Niño  events.

And we certainly can’t predict the events: the current ‘prediction’ is only being made because the El Niño has already begun!

So what do we know?

An Australian Bureau of Meteorology graphic describing the weather patterns in the Pacific Ocean as being either neutral, La Nina or El Nino

An Australian Bureau of Meteorology graphic describing the weather patterns in the Pacific Ocean as being either neutral, La Nina or El Nino

The term El Niño describes a set of linked atmospheric and oceanic conditions. And we understand that the weather patterns in the Pacific Ocean oscillate between three states.

  • Neutral (about 50% of the time)
  • La Niña
  • El Niño (Every 4 to 7 years)

These patterns are so large that they affect the weather right around the globe, and the oscillation between these ‘phases’ is called the El Niño Southern Oscillation (ENSO).

The Australian Bureau of Meteorology have an excellent video description of the phenomenon and its consequences for Australia.

And what don’t we know?

We don’t know what causes the oscillation from one phase of ENSO to another. And so we can’t predict changes from one phase to another.

And importantly, although it is quite conceivable that future Climate Change could affect the transitions from one phase of ENSO to another, we have no idea whether there will be any effect.

And why don’t we know it?

Well obviously, I don’t know the answer to this question. But I think it is this.

ENSO is a linked oceanic and atmospheric phenomenon.

Each of the three phases is self-sustaining i.e. changes in the wind patterns reinforce changes in the location of warm water. And changes in the location of the warmer water reinforce the changes in the wind patterns.

But the variability of the weather is such that it can move the weather patterns from one self-reinforcing phase to another.

And so these planetary scale weather events are triggered by some as yet unknown ‘local’ or ‘short-term’ variability in weather.

Things may improve. As I wrote in my review of Climate Models in the IPCC’s 5th Assessment Report, some models now spontaneously predict ENSO-like behaviour that was not programmed into the model.

And as models of the atmosphere and ocean improve, they will become better able to simulate weather on both the small scale and on the largest scales.

So as our understanding develops it seems likely that changes of ENSO phase will eventually become predictable.

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