Feature Stories | Feb 16 2011
Download related file: El-Nino-La-Nina
(This story was originally published on 8th February, 2011. It has now been re-published to make it available to non-paying members at FNArena and readers elsewhere).
By Greg Peel
As a financial journalist, it is not my place to take sides on the climate change debate. However, I have no qualms in stating my own, honest opinion, taken from a position of simply not being a scientist.
The way I see there are two arguments, and I am not including arguments put forward by industry lobbyists: (1) the earth is warming; (2) the earth is not warming and indeed may be cooling. On the assumption (1) is correct, then: (a) man-made carbon emissions are the cause; or (b) the cycle is natural and while made-made emissions don't help they don't actually make much difference.
My opinion is that which ever of these variations proves to be true, where is the downside in easing the plundering the world's finite natural resources and shifting towards commercially viable alternative and renewable forms of energy? Where is the downside in curbing pollution? I have not heard a viable argument (outside of short term profits and jobs) that suggests why such pursuits are foolish, and many an argument as to why they are not. However, it would seem that in order to achieve such a transition there simply has to be a government mandated price applied to carbon. Exactly how that can best work…well…that's another debate.
So it is from this relatively neutral stance that I make note of a scientific theory that has been gaining some traction of late – that of the Pacific Decadal Oscillation (PDO). I qualify this report straight away by noting the Australian Bureau of Meteorology is so far undecided on the theory's validity but would like to pursue further research before arriving at any opinion.
We are all now familiar with the incidences of El Nino and La Nina. We understand they are related to periods of warming and cooling in the Pacific and other ocean waters. These cycles can be weak or strong, and the recent drought in Australia coincided with strong El Nino periods and the current “wet” coincides with a particularly strong La Nina.
On average, these cycles last six to eighteen months and occur every three to seven years. There are nevertheless no hard and fast rules, and long range prediction is as good as impossible. The best we can do at the moment is see a cycle coming only when it's basically right on top of us, and then monitor when it is the temperature variations begin to turn back again. Meteorologists were able to tell us that a La Nina was apparently beginning late last year but they have only subsequently been able to note that this is a particularly severe cycle.
With the benefit of historical records, research and modelling, the theory of the PDO has arisen. This suggests that overlaying the shorter, sharper El Nino and La Nina cycles are longer wet/dry cycles which last 20-30 years. Both the opposing short cycles come and go within each longer cycle, but typically if the longer PDO cycle is “dry” then El Ninos are more severe and La Ninas are less severe, and vice versa for “wet” PDO periods.
Looking at the data for the twentieth century through to today, 1900 fell in a wet PDO which lasted until 1924, a dry PDO occurred from 1925-46, another wet from 1947-76, and a dry from 1977 on. But given the severity of the current La Nina, which has coincided with the breaking of one of Australia's most severe drought periods, the question is: have we now cycled into the next wet period? The timing is certainly right given a wet period is due. If so, we could be in such a period for another 20-30 years.
Now let me reiterate – I am not a scientist. But out of curiosity, I thought I would create a table to explore the implications of the PDO for Australia back to 1900. It's lengthy, but the table appears at the top of this article (in excel format, for download).
Using data from scientific websites (not Wikipedia) I have created four columns in my table. Column one is each year from 1900 rounded to six-moth intervals. Column two is the periods of PDO, with dry periods represented as red and wet as blue. Column three shows the periods of El Nino (red) and La Nina (blue). Column four shows periods of drought (red) and what the Bureau of Meteorology lists as “severe” flood incidents (blue).
The first impression is that the results are not “perfect”. Droughts have occurred in PDO wet periods and floods in PDO dry periods. There was even one flood (1940) right in the middle of a long drought and El Nino period. According to records, this flood confounded meteorologists at the time but was correctly predicted by aboriginal elders.
What is striking, however, are what I call the “triple red” and “triple blue” periods. Australia's longest droughts have occurred when the PDO is dry and El Nino is occurring. Note the periods 1937-47, 1991-95 and 2000-10 compared to other drought periods. Also note that while all the floods here are noted as “severe”, the most severe floods Australia has experienced prior to 2011 were in 1974 (Brisbane, of which we have all been reminded), 1955 (Hunter Valley, made famous by the movie Newsfront), and 1916 (Clermont Qld, inland from Mackay). Notably the Clermont flood occurred as a result of a cyclone which passed through Townsville. The most severe floods have occurred as “triple blues”, when La Nina has arrived during a PDO wet.
What one can draw from my table, I believe, were the PDO theory to be granted scientific currency, is that if an El Nino occurs during a PDO dry the chance of severe drought is amplified (but not guaranteed) and if a La Nina occurs during a PDO wet the chance of severe flood is amplified (but not guaranteed).
As I suggested earlier, scientists are now considering that the strong La Nina that is now upon us, subsequent to the breaking of the long drought, may signal the beginning of a new PDO wet cycle. If so, farmers can rest a little easier about the question of water supply to crops, but may face more episodes of flooding. The Murray-Darling Basin may rejuvenate itself long before politicians come up with a viable solution. Miners may well be in for more regular incidents of lost production from flooded mines.
I personally am not endorsing anything here – just throwing the subject up for discussion. It is, however, interesting to note that what one might call a “skeptical” school of scientists (and again I don't mean any on the payroll of Exxon etc) points to the PDO as a possible explanation for global warming beyond that of man-made emissions.
I also note, again without qualification, that to jump on Australia's recent weather as “confirmation” of the impact of man-made emissions is to ignore the wider sample set. For example, the 2011 Brisbane flood did not quite reach the height of the 1974 Brisbane flood. Cyclone Yasi did not quite prove more severe than Cyclone Tracy, which also hit in 1974. Back in the seventies scientists were actually worried the earth was cooling, such that a new Ice Age may be upon us.
Food for thought.
