The Bureau of Meteorology has officially declared that we are in an El Niño, shifting its tracker from ALERT (a greater than 70% chance of El Niño forming) to an actual event.
Speculation began in early 2014 that the world would see an El Niño, possibly a significant “super” event, by the end of that year. However the event development hit a few setbacks, and many thought the El Niño was already dead.
In March this year, US National Oceanic and Atmospheric Administration officially declared that the “most-watched” 2014-15 El Niño had finally arrived. Now our own Bureau has followed suit.
So what’s going on? And how severe could the 2015-16 El Niño turn out to be?
Ghosts of El Niño past
El Niño usually develops over the southern autumn-winter, peaks around Christmas, and decays in the southern autumn.
So this event is unusual as an El Niño would generally be decaying by this time of the year, but observations over recent weeks show otherwise. Sea surface temperatures in the El Niño core region (eastern equatorial Pacific) are actually still warming and the pattern is now looking more like a classic El Niño.
In fact, the warm anomaly over the eastern equatorial Pacific – the typical indicator for an El Niño – has in the past three weeks exceeded 1C. Assuming this El Niño peaks at Christmas of 2015, this recent 1C temperature anomaly is unprecedented during the autumn of all developing El Niño years since at least the early 80s.
We’ve seen a similar size temperature anomaly in the autumn of 1987, but that was in the middle of two, back-to-back El Niño events: the summers of 1986-87 and 1987-88. At that time ocean heat under the surface was already on the decline following the peak of El Niño on Christmas 1986, while sea surface temperatures received a second boost to peak in August of 1987.
This year though it looks like the 2014-15 El Niño is yet to reach its peak. Both the temperature anomaly and amount of ocean subsurface heat are still building. The ocean heat has in fact surpassed last year’s massive value and is now rivalling that during the development of the 1997 super El Niño.
Read more: The Conversation