ENSO Update – A Bounce Upward
Posted by The Diatribe Guy on June 8, 2009
The ENSO Index has been updated for May month-end, and we see a two-month average index value of 0.344.
This is the first reading that is positive since last July, but last year the positive index values barely reached above 0 for a short, two-month stay before dipping back into La Nina territory.
The new value, strangely enough, seems to have certain pro-AGW members of the blogosphere salivating about how it looks like there is a new El Nino on the way. Interestingly, the same people who wring their hands about what warming is going to do to us can’t seem to wait for higher temperatures driven by a new El Nino. They are as much as telegraphing the fact that they will use El Nino-driven elevated temperatures, should they occur, to assist in their case for the idea that CO2 is increasing temperatures. It is unfortunate that they will likely have a voice in this claim – reasonable or not – since there is no correlation between the ENSO cycles and Carbon Dioxide levels (at least that I am aware of).
In the meantime, we can look at the data to see what’s going on with the index. El Nino and La Nina have somewhat sketchy official designations, but I think it’s a fairly common rule of thumb to say that when the index reads above 0.5 for three consecutive months, we’ve got ourselves an El Nino. When the index goes below -0.5 for three consecutive months, it’s a La Nina. I have an interesting observation regarding that a little later on. Based on that rule of thumb, it looks like we’ve come out of a recent La Nina in March. The last one wasn’t particularly strong or lengthy, though it did come on the heels of a stronger one the year before.
In April, the index increased quite a bit, though the 2-month average was still negative. The May value increased again from that level. However, talk about a new El Nino, while entirely possible, is a bit premature. We’re not even at one data point that qualifies yet.
We know that both the upside and downside happens whether we’re in a cooling or warming cycle, so regardless of what side of the argument you are on, you can’t really make any wild claims about what the latest cycle means. It’s probably more accurate to assess the ENSO index over time.
I have updated the best-fit wave pattern against the available ENSO data and shown it below:
The best-fit cycle shows around a 60-year wave pattern. We are now entering the downside of that wave. One thing I noticed is that the best-fit requires a vertical shift upward of the wave. This means that the zero-point of the index should probably be higher than it is. The latest maximum, for example, reached a level of 0.4687 on the crest of the wave (meaning that El Nino will be elevated by nearly half a degree during that time) and the latest trough of the wave was -0.3966 (El Nino will be lowered by about 04 tenths of a degree). The index should really be calibrated down by about 0.05 of a degree. Otherwise, the significance of El Nino will be overstated while the corresponding La Nina will be understated.
The best-fit ENSO wave pattern actually has a negative linear trend that makes a longer-term extrapolation questionable. I didn’t particularly believe that element of it. It fits the current data well, but the gut-check test tells me it would be best to simply leave this parameter at zero. When I run that, the least-squares fit is only marginally worse, but the long-term, extrapolated values make a world more sense. The graph as shown is not much affected, and the same vertical effect is still shown. Just another lesson in modeling, where simpler is often superior. The chart above excludes a linear trend assumption.
According to the chart above, the cold phase of ENSO is just beginning. Yes, we will have El Ninos, but the next 25 years or so will probably look closer to the left half of the chart than the right half of the chart in terms of magnitude of the peaks in relation to a zero index value. In relation to the wave, the peaks seem to ride the wave nicely.