Climate change to turn up heat

27 Jan, 2015 07:08 AM
It means more occurrences of devastating weather events

GLOBAL climate is likely to become increasingly prone to extremes with super La Nina and El Nino events in the Pacific to almost double in frequency this century, according to Australian-led research.

In a study published on Monday in the journal Nature Climate Change, an international team led by the Commonwealth Scientific and Industrial Research Organisation's (CSIRO) Cai Wenju found extreme La Nina events forming in the Pacific would increase from about one in 23 years to one every 13 years because of rising greenhouse gas concentrations in the atmosphere.

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  • The work, based on 21 climate models, comes a year after a team led by Dr Cai published a paper finding extreme El Nino events would double in frequency from once every 20 years to once per decade. Total event numbers remain little changed but their intensity increases.

    About three-quarters of the additional super La Ninas would follow in the year after an extreme El Nino event, potentially adding severe strains to societies and ecosystems.

    "It means more occurrences of devastating weather events, and more frequent swings of opposite extremes from one year to the next, with profound socio-economic consequences," the paper concludes.

    The El Nino-Southern Oscillation is a major driver of climate variations. In El Nino years, the eastern equatorial Pacific warms relative to the west, slowing easterly trade winds and drawing rainfall away from eastern Australia and parts of South East Asia with droughts common.

    La Nina years involve the reverse process, with heavy rain and floods in the western Pacific but drier conditions prevailing in the east. The ocean also tends to absorb more heat during those years, placing a drag on surface warming.

    Global records count four extreme La Ninas in 1877, 1972-73, 1988-89 and 1998-99. The latter event followed a year after a super El Nino, and in the future such back-to-back extremes will double in frequency to happen every other time, Dr Cai said: "Climate change is going to increase the sequence in which you have an extreme El Nino followed by an extreme La Nina."

    The eastern equatorial Pacific – where El Ninos form – is warming faster than the western Pacific and both are heating up faster than the central Pacific.

    "In a warming world it takes smaller temperatures to generate those kinds of shifts (to either an extreme El Nino or La Nina) because the warming is not uniform," Dr Cai said.

    The tendency towards more extreme conditions has been noted in the latest climate projections released this week by the CSIRO and the Bureau of Meteorology (BoM).

    While droughts can be devastating the impacts tend to be slower to build compared with floods.

    "While wet years are typically good for agriculture and for topping up our dams, the extreme La Ninas tend to lead to more flooding and damage," said Kevin Hennessy, group leader of CSIRO's climate unit. "We find that there's a significant increase in the one-in-20 year extreme daily rainfall events right across Australia in the future."

    Dr Cai and his team noted that in the super La Nina event of 1998-99, Bangladesh suffered one of its worst floods, with about 50 per cent of the nation and 30 million people affected. China also reported floods and storms that killed thousands and displaced more than 200 million.

    The Atlantic hurricane season also tends to be more active than usual in La Nina years, as it was during the extreme event.

    Dr Cai said the modelling of extreme Pacific conditions was based on the current high greenhouse gas emissions trajectory.

    "If we do nothing, this is what happens," Dr Cai said. "It's an awful result."

    The next big area of study in the field is likely to focus on how the size of regions affected by floods and their intensity will change, he said.

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    3/02/2015 6:54:10 AM

    Silly Susan, it's very worrying that you cannot accept the science that the warming stopped 20 years back! Silly Susan, it's also worrying you cannot accept the science that the warming we had till then was normal and GOOD. Silly Susan, it's even more worrying that you think that maybe cooling is better than warming. Silly Susan.
    3/02/2015 7:07:39 AM

    Susan, can you tell us (because your close cousin Nico seems to have no idea ) how much warming has there been in the last 18 years?
    3/02/2015 12:47:35 PM

    Susan, check out the temp graphs at CRU UEA & also NASA GISS which both show a number of graphs all with similar plots ie rising temps up to around 2000, thence a slight reduction. Perhaps those that claim temps are still rising would care to explain & give their source/s that differ from the 2 given above.
    3/02/2015 7:02:05 PM

    Gumtree & FB - you are unable to comprehend that I am only interested here in the science involved which does not support your contention that the globe has stopped warming. You are denying the rising sea level data which are abundantly clear. You just go on concluding that global warming has stopped, a conclusion you base on the current pause is global air temperature rise The situation now is that proportionately more heat is going into the oceans than into the air. To understand this google "Ocean depths heating steadily despite global warming ‘pause’.
    4/02/2015 5:17:39 AM

    Susan, where are you? Can you please answer my question? Tell us all exactly in deg C how much warming has there been in the last 18 years? Your silence tells me there has been....... NONE. And who cares if there was, warm is good and cold is bad. But of course, Susan, we all know you don't really believe your own scaremongering bunk. Do you, Susan?
    4/02/2015 5:27:09 AM

    And yet even more proof, Susan, that you are wrong with news of record cold and snowfalls hitting the US today. /us/weather/index.html
    4/02/2015 6:05:20 AM

    Sure Susan, and all this hidden heat in the oceans is being caused by a piddly amount of anthropogenic plant food? I think not. I think you have a real problem dealing with reality.
    4/02/2015 6:43:12 AM

    Susan, why is it you insist that the very small sea level rises, not the devastating rises predicted by the alarmists, can only be because of ocean warming. There are many possible causes and I will list a few. Silt washed down rivers and into the oceans all around the world must cause a certain amount of sea level rise. The amounts of rubbish and REAL pollution continually dumped into the seas must cause a certain amount of sea level rise. The increase in ships transporting cargo all around the world and the reclaiming of coastal areas (sea) for human habitation must cause levels to rise.
    4/02/2015 7:47:24 AM

    What are you looking at, daw? The various datasets, which are derived from different instruments in different locations (meaning that they give slightly different readings), all show a slowing of the *rate* of surface warming during the past two decades, but the graph continues to rise. There has been no "pause". And more than 90% of the increased energy is being absorbed by the oceans. See: /graphs_v3/
    4/02/2015 8:17:56 AM

    "A slowing of the rate" surely if global warming was directly connected to GHG emissions there would be a fastening of the rate of warming like the models predicted but got so horribly wrong. There is something very wrong with the whole CAGW idea.
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