Pacific shift may accelerate warming

30 Dec, 2014 08:20 AM
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26
 
This could be the start of another ramping up of warming

WITH 2014 likely to be declared the world's hottest year on record, the last thing the planet needs is a climate shift to turbo-charge the global warming already under way.

While it's an early call, a measure of surface temperature differences in the Pacific shifted to a positive reading in the five months of November, according to the US National Oceanic and Atmospheric Administration – the longest such run in almost 12 years.

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  • Known as the Pacific Decadal Oscillation, the El Nino-like pattern typically lasts 15-30 years and is understood to operate as an accelerator on global surface temperatures during its positive phase – and a brake during its negative phase – as the ocean takes up fluctuating amounts of the extra heat being trapped by rising greenhouse gas emissions.

    "It certainly could be an early sign of a change but you'd probably want to see another year or two before it's a genuine phase shift," Matthew England, a professor at the University of NSW's Climate Change Research Centre, said. "This could be the start of another ramping up of warming."

    The last positive phase of the PDO, also known as the Interdecadal Pacific Oscillation, ran from about 1978 to 1998, a period of a rapid increase of surface temperatures. Since then, temperature increases have flattened out, despite an increase in greenhouse gases, as oceans have taken up more of the excess heat.

    Even with the negative-PDO drag - worth about 0.2 degrees in global average air temperatures a decade - 2005 and 2010 both topped the 1998 record annual global temperatures. The first 11 months of 2014 were the warmest on record and with ocean temperatures remaining exceptionally warm, this year is very likely to set a fresh high, according to NOAA, the Bureau of Meteorology and other agencies.

    In positive-PDO periods, the tropical Pacific is relatively warm and north of about 20 degrees latitude, it should be cool, said Shayne McGregor, a UNSW research fellow, said: "It's definitely consistent with what we've seen in tropics."

    "During a positive PDO phase, you'd expect temperatures to keep climbing again as they did in the 1980s and 1990s," Dr McGregor said, adding that as PDOs are measured by rolling 11-year averages, it will be a while before any shift becomes clear.

    Cai Wenju, a principal scientist with the CSIRO, agreed it will take time before any index shift is clear. Still, the next positive phase would likely bring faster warming at the surface and worsening drought conditions for Australia and much the region, he said.

    "When it is positive, it tends to give us less rainfall because convection is shifting away from the western Pacific," Dr Cai said, adding that floods worsen in Ecuador, Peru and elsewhere on the Pacific's eastern rim.

    While 0.2 degrees either way can set new global records or stall the march higher of surface temperatures – about 0.05 currently separates the five warmest years – over the longer term, global warming will swamp even interdecadal fluctuations, Professor England said.

    "If we stay with relatively flat temperatures for another five years, it means nothing for global warming projections for the end of the century," Professor England said, noting temperatures may then be 4-7 degrees hotter on current greenhouse gas trajectories.

    "The chance of that tiny 0.2-degree decadal signature overwhelming the greenhouse warming becomes vanishingly small."

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    READER COMMENTS

    Matti
    30/12/2014 9:23:08 PM

    As for "a rapid increase of surface temperatures", the planet warmed by a whopping 0.3 degrees over 20 years. Hardly rapid! There is no statistically significant difference in the warming rates between the late 1800's, early 1900's and between 1978 and 1998. There is no "signature" for CO2 "forcing" in the temperature record. This fact is acknowledged by Professor Phil Jones of CRU East Anglia. The recent warming was not "rapid" nor "accelerating" as climate alarmists would have us believe.
    Albert Einstein
    31/12/2014 6:14:11 AM

    Thank you Matti for some common sense, its about time the CO2 myth died.
    nico
    31/12/2014 9:35:26 AM

    Qlander, if your education had included high-school science you would be aware that science deals in probabilities. First comes the observation and measurement, then the theory, then the prediction. Prof England is simply using normal scientific language.
    Qlander
    31/12/2014 10:23:10 AM

    Most scientific models are presented in a straightforward way, and it’s not difficult to see how they can be falsified. If a model is so vague and all-encompassing that is compatible with all possible evidence, then it cannot be falsifiable. It cannot, therefore, be scientific.
    Gumtree
    31/12/2014 10:57:49 AM

    And if the predictions end up being wrong Nico , which they have been so far then we go back to the observation and evidence and start again . We don't stubbornly stick to the predictions when they are clearly incorrect . As you say there are a lot of probabilities , so nothing is set in concrete. We need to be a little flexible.
    nico
    31/12/2014 11:28:37 AM

    Which predictions did you have in mind, Gumtree? Of course, climate predictions have been wrong on occasion, and have accordingly been corrected. That's how science works. When something is shown to be wrong, the next step is to look for a reason. Climate does not "just happen".
    Matti
    31/12/2014 11:49:12 AM

    This is AGW/CO2 theory: "Another thing I must point out is that you cannot prove a vague theory wrong. If the guess that you make is poorly expressed and rather vague, and the method that you use for figuring out the consequences is a little vague – you are not sure, and you say, ‘I think everything’s right because it’s all due to so and so, and such and such, do this and that more or less, and I can sort of explain how this works’, then you see that this theory is good, because it cannot be proved wrong!" - Richard Feynman
    Qlander
    31/12/2014 1:57:29 PM

    nico you, Prof England, and the rest of the climate 'faithful' would do well to watch this. - Take particular note from 16:50 to 24:00, this is a real scientist talking.https://www.youtube.com/w atch?v=MIN_-Flswy0
    nico
    31/12/2014 3:02:02 PM

    Poor Richard Feynman, who died in 1988. He has been taken up by the anti-science denialists, but few of them realise that he was a most rigorous scientific thinker. "Nature cannot be fooled" he said.
    Matti
    31/12/2014 9:56:09 PM

    Nico - all predictions have been wildly wrong using climate models. Let me just explain all the "Hottest evah!!!" temperatures we constantly hear about, apart from all the "adjustments" and "homogenisation". Modern electronic thermometers will instantly record brief fluctuations in temperature (eg. a momentary hot breeze, common with UHI) whereas the old style bulb thermometers would not register this. All modern temperature readings need to be adjusted down due to this, not up as they have been.
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