Digital Diatribes

A presentation of data on climate and other stuff

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.

enso-overall

The overall ENSO data are presented here. There is a slight linear trend upward over time, which does show a general rise in the index. However, more important than this is the persistence in Index values above and below the line. General observation seems to indicate that prior to the 1970s much more time was spent in La Nina territory, and since then more time has been spent in El Nino territory.

enso-overall

The same basic picture is presented here with 12-month smoothing. It's a little clearer to see with the jagged edges removed, but there are still a lot of cycles apparent.

enso-overall

With 36-month smoothing we can begin to see the persistence a little better. There seems to have been a flip in the mid-70s that took us from a persistent cool state in the ENSO index to a persistent warm state in the ENSO index. This corresponds with the switch in thinking in the scientific community that we were heading into an ice age to a shift in concerns about human caused global warming.

enso-overall

With 5-year smoothing, the persistence becomes very apparent. The data index starts in 1950, so that's my starting point. The period from that time to the average ending 1979 are below the zero line with two brief and low-magnitude exceptions. Suddenly, it's as if things were flipped upside-down and we see a continuous 5-year average index value above zero for nearly a 25 year period. We finally saw a single, relatively low-magnitude dip (on a five year basis) for the period ending in 2003. With the recent La Nina period and current lower values, it looks like we may breach the zero point again soon.

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.

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6 Responses to “A Quick Look At the ENSO Index (Another La Niña on the Way?)”

  1. docattheautopsy said

    I love data! Your site is a tremendous resource! Thanks for all the updates!

  2. […] Diatribes (whom I’ve now blogrolled).  The most significant of this information is the from this post, which seems to indicate another La Nina event is underway.  He’s spot on when talking about […]

  3. […] on Arctic…Jeff Id on November 2008 Update on Arctic…Global Warming Round… on A Quick Look At the ENSO Index…Bob Tisdale on 2008 Update on Antarctic Tempe…Overall temperature … on 2008 Update on […]

  4. […] Manns, Ph.D., P… on Pacific Decadal Oscillation (P…Pacific Decadal Osci… on A Quick Look At the ENSO Index…Jeff Id on November 2008 Update on Arctic…Environment and natu… on November 2008 […]

  5. […] I also took a look at the ENSO index over timeand showed that, while the ENSO cycle is much shorter-term, it also has been in a persistently warm state since the late 70s. I was one of the first I am aware of to point out the very recent readings in the Index pointing to another La Nina (there is some debate as to whether or not it is a “true” La Nina, since the cooler PDO could be driving this measure down. That seems silly to me. If you’re going to start arguing about influences to the index, then you can’t stop at the PDO.) In any case, the ENSO index is also running into recent negatives, and the persistent warm state appears to have finally come to an end. […]

  6. […] I’ve taken a look at the ENSO index, and the longer-term persistency of it. I’ve done the same with the PDO, and also with sunspot counts. All these cases tend to point to the persistence of cyclical events. These are also the kinds of things that can change suddenly. Carbon Dioxide may be a nice theory for long=term, gradual trends, but it makes no sense at all as an explanation for a step function. A review of the Mauna Loa Carbon Dioxide data, for example, simply shows no great leaps and bounds in the concentration of carbon dioxide in our atmosphere. […]

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