A Quick Look At the ENSO Index (Another La Niña on the Way?)
Posted by The Diatribe Guy on November 21, 2008
Don’t look now, but the ENSO Index is once again entering “La Niña” territory, which is generally recognized as the point where the ENSO index falls below a deviation of -0.5.
If this continues, we are sure to see the effects of it manifest in the way of cooler weather and varying precipitation events by regions affected in one way or another by the phenomenon. And if this occurs, then we can expect to see a perpetuation of the negative trend lines we have seen in recent years. This will be met with a predictable response by AGW supporters whenever they see a chart of negative trend lines: “Well, of course it’s negative! It’s because of La Niña on the heels of that really big El Niño a decade ago!”
Of course, they may well be right in that, so I will give credit where credit is due. The only problem with the argument seems to be this belief that prior to 1998 the ENSO Index either fluctuated perfectly between cool and warm, or didn’t fluctuate at all. Therefore, the 30 year warming trend is really because of people and has nothing much to do with the ENSO index, and only the cooling of the last decade is a reflection of aberrations in the ENSO swings.
I decided to take a quick look at the index with some simple charts. The presentation isn’t rocket science. Just plot the values, and then take a look at what happens when you collapse them into 12-month, 36-month, and 60-month periods. These collapsed periods will provide insight into not just short-term ENSO fluctuations, but longer term variations.
Why is that important? It’s simple physics. Suppose you have a heating source that gets very warm. The energy emitted from that source warms the surrounding area. Now, cool that heating source down. The surrounding area, depending on insulatory effects and the like, will cool down also, but at a slower rate. If you warm that heating source up again before things cool back down to “normal” then you are now transmitting more heat energy into your area but starting at a warmer base. If you keep doing this over an extended period of time, you will continue to reach higher and higher temperatures.
Contrast this to a perfectly cyclical situation. Your heating source warms, gets turned off, then an A/C unit turns on, gets turned off, then the heating source starts again, and so on. While short-term temperatures will rise and fall in your area, the overall average will be fairly constant.
If the ENSO index shows a persistent positive or negative value when smoothed over longer-period averages, then it is an indication that temperatures have been – at least in part – driven upward or downward by that persistent activity.
So, let’s take a gander at the charts.
The main point here is not to suggest that recent La Niña activity doesn’t play a part in the recent cooling trends. In fact, I strongly believe it plays an important part in that. But when this argument is applied as a way of disregarding recent cooling trends but is not similarly considered for the previous 25 year period of significantly and persistently positive ENSO indices, then it is a disingenuous criticism of the validity of recent trends.
Also, to reiterate, the other point I wish to make clear is that you cannot simply say that the ENSO Index at a given time simply contributes to temperature from the base average. Persistence in either a high or low state will continue to affect current temperatures relative to previous temperatures, not average temperatures. This is an important point in understanding why a simple trend line on contributing factors don’t tell the whole story. The same is true of a similar exercise I did with regard to sunspots.