“IT takes a lot to make a Bureau climatologist go 'wow' these days, but on May 18, there were a lot of 'wows' round the office.”
At first glance it seems weather geeks are easily wowed, because the reaction that the Bureau of Meteorology’s Andrew Watkins is describing was to a figure, 2.4°C, to be exact.
That’s how much warmer than normal the central Pacific could be by spring 2015, according to an aggregation of predictions from the world’s main climate models.
Warming of the central Pacific drives the El Niño cycle. Climatologists consider 0.8°C to be the threshold warming necessary to produce an El Niño.
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That threshold was breached only a few weeks ago, when the Bureau decided that rising ocean warmth and shifting atmospheric cycles had linked to a degree that it could make the call that a 2015 El Niño was “on”.
Now the models are forecasting a rapid escalation of ocean temperatures to 2.4°C above average by spring, “the warmest model update most of us had ever seen”, Dr Watkins wrote in a blog post.
The big, infamous El Niños of the late 20th Century - 1982, 1997 - were driven by a similar magnitude of warming.
So, will 2015 be a year of drought, fire and heat? That’s a possibility, Dr Watkins said, but it’s by no means certain.
May is the month when the “skill” of global climate models in predicting El Niño conditions jumps from low to high.
And the models are now much more in agreement than when the confused messages about the onset of an El Niño were broadcast in 2014.
“This time last year the models were also warming up, but at least three models were not that sure it would amount to anything,” Dr Watkins said.
“And indeed they were right.
“This time we have far more warming too - at least double last year's numbers - and all models are emphatic about an event occurring.”
“Emphatic” is still not 100 per cent certainty. The models remain a guide to probabilities.
“As we move further into the southern winter, if models are still showing very high values then we will get greater and greater confidence that this could be a big event, such as a 1982 or 1997 in terms of strength.”
Then there are the variable impacts of El Niño events.
More often than not - 17 out of the 26 El Niños since 1900 - the phase is associated with drought in Australia. But there are those other years.
Every El Niño produces drier conditions somewhere in Australia, Dr Watkins said, so any land manager would be prudent to manage for this possibility.
But every El Niño is different, because around the globe a range of other atmospheric and ocean cycles are influencing climate, along with factors that never make it onto a weather map - things like soil moisture, Antarctic ice, aerosols from Asia.
Australia has experienced drought in weak El Niños (2006) as well as strong El Niños (1982); and reasonable rainfall has been recorded in strong El Niños (1997) as well as weak (1969).
Some models are also pointing to a positive Indian Ocean Dipole (IOD) later in 2015.
The IOD has greatest influence over rainfall in central and south-eastern Australia. A “positive” IOD - when the ocean is warmest to the west, on its African side - usually signals reduced rainfall in these parts of Australia.
However, Dr Watkins said there is some way to go before the Bureau can be sure that this possible reinforcement of El Niño’s drying effects is a reality.
His advice for farmers and others concerned with climate is not dissimilar to any other year: weigh the risks with the best tools available to you, and act accordingly.