Shedding light on El Niño uncertainty

28 May, 2015 02:00 AM
Comments
25
 
Photo: Chad Clark
Weigh the risks with the best tools available to you, and act accordingly
Photo: Chad Clark

“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.

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    FarmOnline
    Matthew Cawood

    Matthew Cawood

    is the national science and environment writer for Fairfax Agricultural Media
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    READER COMMENTS

    Qlander
    28/05/2015 9:14:30 AM

    Get back to me when 'could' becomes 'is'.
    nico
    28/05/2015 11:03:52 AM

    Poor Qlander. Not a clue. He (or she?) still doesn't understand that science is based on probabilities. Qlander, we might get back to you when you have done a little more reading and have gained some understanding, even just a glimmer, of the scientific process.
    Qlander
    28/05/2015 1:09:48 PM

    Some of us live in the real world of business, nico. Banks don't operate on the basis of 'if' or when I 'could' meet my commitments.
    John Carpenter
    28/05/2015 1:10:16 PM

    "Science is based on probabilities",is Nico an SP bookie?No science is based on certainties and theories that can accurately predict the physical world.
    Gumtree
    28/05/2015 1:11:11 PM

    " WE might get back to you " ? Since when Nico did you start working for the BOM or any other scientific body ? God help us all if you do , no wonder science is so screwed up these days.
    Qlander
    28/05/2015 2:39:59 PM

    John Carpenter - Nico is talking about the new 'political science' where you apply for a grant, to study a theory that can't be proven. In which case computer models become the new reality.
    nico
    28/05/2015 7:26:03 PM

    Qlander, do your homework. Have you never heard of the Stock Exchange? Or international exchange rates? Of course "the real world of business" operates on probabilities. The difference is that science also operates on rigorous observation and measurement, leading to logical predictions. And this is why predictions have degrees of certainty. Nothing is absolutely certain, but some things have a high degree of probability.
    Bill Pounder
    28/05/2015 11:18:17 PM

    The BoM might have a dud call here. The oceans were much warmer during the 1998 El Nino vs 2015, (with a blink comparison attached), also, as an aside, note the lack of data above India & in the Andes. The reason being is, that at 14,000 feet there is no atmosphere & therefore no data:- https://twitter.com/SteveSGoddard /status/603273184524242944 The blink maps are found here, but it's tricky:- http://www.remss.com/measurements /upper-air-temperature
    Logic
    29/05/2015 4:37:50 AM

    Nico, only weather science is based on probabilities.
    Bluey
    29/05/2015 4:54:41 AM

    Be great when BOM can get the next days forecast close to what actually arrives more often without telling us what they predict is going to happen months out
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