Most of us who follow climate science closely have been watching with interest the developing situation in the Pacific Ocean with the Southern Oscillation and the predictions that we are headed for an El Nino..and a big one at that. First, for anyone unaware of what I’m talking about, this short video explains things very nicely and simply.
What this video doesn’t discuss are the implications for the global climate of the Southern Oscillation and in particular what the relative strength of an El Nino does. It is hypothesised that during neutral and La Nina years, energy from the sun accumulates in the deep ocean and as the Southern Oscillation switches to an El Nino phase, surplus energy is released at the ocean surface/air interface, raising the average surface air temperature. With the enhanced greenhouse effect caused by anthropogenic emissions of CO2 and other greenhouse gases, more of this heat is trapped and over time, the temperature goes up.
What becomes obvious when looking at global surface air temperature data is the difference in the highs between El Nino years, La Nina years and neutral years.
What this graph shows quite clearly is that in any given period El Nino years are relatively hotter than La Nina and neutral years. 1998, the year that AGW deniers like to cherrypick was an exceptional year as the preceding El Nino was an extremely strong one. An explanation for how the Southern Oscillation Index (SOI) works and what constitutes an El Nino, a La Nina and a neutral state is provided by the BOM.
Sustained positive values of the SOI above +8 may indicate a La Niña event, while sustained negative values below −8 may indicate an El Niño event. Values of between about +8 and −8 generally indicate neutral conditions.
The following graph shows the SOI for the period 1994-1997. Take note of the values for the very strong El Nino of 1997-98. The strength of that El Nino was reflected in the average global surface temperature of 1998 as mentioned previously.
While the tropical Pacific Ocean remains El Niño–Southern Oscillation (ENSO) neutral, the chance of an El Niño occurring in 2014 has increased. The latest climate model survey by the Bureau shows that the tropical Pacific is likely to warm in the coming months, with most models showing sea surface temperatures reaching El Niño thresholds during the southern hemisphere winter.
Observations indicate that the tropical Pacific Ocean is currently warming. Following two strong westerly wind bursts since the start of the year, waters below the surface of the tropical Pacific have warmed significantly over the past two months. This has led to some warming at the surface, with further warming expected in the coming weeks. The Southern Oscillation Index (SOI) has dropped to –13—the lowest 30-day value since March 2010—but would need to remain firmly negative for several weeks to indicate the atmosphere and ocean are reinforcing each other.
A month or so ago, researchers, using a different data set predicted an El Nino for this year giving a 76% likelihood of one developing and a big one at that. It is now being reported that US atmospheric scientists are also predicting a very large El Nino.
The sub surface temperature of the eastern Pacific Ocean is measuring an ‘astounding’ six degrees warmer than normal for this time of year.
A team of US atmospheric scientists says that points to a major El Nino event forming to rival the record event nearly 20 years ago.
El Nino is associated with dry conditions and reduced monsoons in Australia and Indonesia, but wetter weather in Central America.
Paul E. Roundy, associate professor of atmospheric science at the University at Albany, New York, says there’s been a series of westerly winds that amplify waves, moving warm currents of water thousands of kilometres and moving a surge of warm water from west to east.
That pushes the warm water to considerable depths.
“It’s close to a 70 or 80 per cent chance of a major event,” Associate Professor Roundy said.
“The Climate Prediction Centre would disagree and set the rates lower.
“But I’m thinking in the context of what we observe in the ocean right now, is consistent with that kind of major event developing.
“No guarantee! But it is consistent.
“The only time that (the six-degree warming) has ever happened before, this time of the year, was in that March of 1997 event. So it highlights the risk, even though there’s only one event like that.
Indications are that a huge Kelvin Wave has been developing and a large pool of very warm water is popping up close to South America, both indicators of a major El Nino event.
This Kelvin Wave is of historic strength, clocking in at roughly +5.64º C above normal as of March 20th. It was at +5.35º C on March 13th, marking a +0.29º C change in just 7 days. Even more concerning is the push to the surface, and how the KW continues to strengthen. As we look to see westerly winds continue from the western Pacific, I have little doubt we’ll see an El Nino be declared in the next 4-10 weeks.
So, I guess time will really tell but all the indicators are pointing to a large El Nino this year and we are probably due for one anyway. If I was living in southeastern Australia in a bushfire prone area, I’d be thinking about planning for the worst. As for our farmers, I’m not sure what they can do about the likely super-drought conditions that will result from the El Nino overlaid on the already long-term diminishing rainfall conditions experienced across most of southern Australia.