For months we have been told how this is a strong El Nino, similar to the “Super El Nino” of 1997-98. How does it really stack up?
As data for sea surface temperatures are not available before 1950, the Southern Oscillation Index (SOI) data from 1876 are the best for long term analysis. In this post I am using SOI data from the BOM archive.
The Bureau uses sustained (three month mean) SOI values of 7 or less as an indication of El Nino conditions. This plot shows three month mean SOI values from 1876:
Fig. 1: Three month mean SOI values from 1876
It is plain that as of November 2015 the three month mean is still nowhere near as low as it has been in several past El Ninos (and 1997-98 was not the lowest either!)
The next graph compares the length of El Ninos.
Fig. 2: El Nino length
Plainly 1941-42 was the one to beat, and El Nino conditions will need to persist for another 18 months to compare. Another four to six months is more likely, and of course there could be a double up of another El Nino next year (as happened in the 1990s).
I next calculate the relative strength of El Nino conditions, by summing the (inverted) SOI values of all months in El Nino i.e. that have a three month mean of -7 or less.
Fig. 3: El Nino cumulative strength
Unless we get another six months of values below -20 we won’t beat 1997-98 into fourth place.
Of course, we are only in the seventh month of this El Nino- how does it compare with this stage of previous El Ninos?
Fig. 4: Three month mean SOI value for seventh month of cycle
The November 2015 value is the black dot- in sixth place.
Compared with the strength of previous El Ninos, the seven month value of this one is also in sixth place:
Fig. 5: Cumulative strength in seventh month of cycle
Another interesting method of comparison is to change the definition of “El Nino” to “El Nino or Neutral” i.e. periods between La Ninas.
Fig. 6: Length of El Nino or Neutral conditions
Note the two periods of nearly seven years without La Ninas in the 1980s and 1990s, separated by a 12 month La Nina- immediately followed by the 1997-98 event, and then another five year period. 2014-15 is not unusual.
The integral of SOI values, as a measure of the strength of El Nino:
Fig. 7: Cumulative strength, El Nino or Neutral conditions
Currently this event is in 12th place, and if it runs strongly for another six months it could sneak into seventh place.
Compared with other events, at the 22nd month this event ranks fourth.
Fig. 8: Cumulative strength at 22nd month of cycle
The current El Nino event is not going to break any records, unless it continues for several years!
It is nowhere near the most intense, nor the longest, nor the strongest.
It cannot compare with the intensity of previous El Ninos, as measured by three month average values, such as in 1896, 1905, or 1983.
It cannot compare with the length of previous El Ninos, such as the 1941-42 event, or the series of years of El Nino and neutral conditions in the 1980s and 1990s.
Depending on the measure used, it is fourth or sixth strongest for this stage of the cycle. If it continues strongly, its final strength might reach seventh or perhaps even fourth place. But that is unlikely. According to the Bureau, this event will peak before the end of 2015, and finish by mid-Autumn.
Fig. 9: Model outlooks for El Nino end
Despite the hopes of the global warming enthusiasts, this is just another moderately strong El Nino which may cause a spike in world temperatures in the first half of next year, but is nothing to get excited about.
Tags: El Nino