Climate change to turn up heat

27 Jan, 2015 07:08 AM
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101
 
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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    READER COMMENTS

    FB
    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.
    FB
    3/02/2015 6:20:20 AM

    You have no idea what you are on about, Susan, the warming during the last century which has now stopped was mild, normal and beneficial. What is your problem?
    Bill Pounder
    2/02/2015 9:59:12 PM

    Back to to the drawing board Susan, the UN's IPCC accepts that approx. 97% of the increase in CO2 since 1850 is from nature & that at 95% water vapour is the principal Green House Gas (GHG). Further, RSS lower tropical mean satellite data shows no warming for 18+ years, & both UAH satellite data & HADCRUT4 global mean shows no warming for 14+ years. All are accepted temperature data sets. Where's your raging out-of-control CO2 of which you are so afraid? Hint, do some basics. http://climateaudit.org/2008/05/0 9/where-did-ipcc-1990-figure-7c-c ome-from-httpwwwclimateauditorgp3 072previewtrue
    Love the country
    2/02/2015 6:03:22 PM

    Nothing to do with what we do at ground level, it's the millions of lts of aviation fuel burning from the planes going around the world 24/7, that effecting the ozone, Big time
    Susan
    2/02/2015 4:32:58 PM

    FB and Gum Tree, everyone knows that great climatic changes have occurred through past geological ages. You should have understood that i was writing in the context of recent times - say the last 100 years. Over that time the globe has warmed and the warming is continuing - this cannot be disputed. However you seem unable to accept this and it is worrying that some people are unable to accept facts. Am I correct in assuming that you are unable to write in these columns that you believe the above warming is occurring. What is causing the warming is, of course, a separate matter.
    FB
    2/02/2015 1:35:10 PM

    No, your factually wrong, Susan. The earth has been cooling since the Holocene climate optimum some 9000 to 5000 years ago. So stop posting silly alarmist global warming rubbish from denialist blogs. Try to stick with real science and known history. That way we won't call you Silly Susan.
    Gumtree
    2/02/2015 12:09:39 PM

    Susan, don't be so silly, global warming and global cooling (climate change) has been going on since the earth formed an atmosphere 4 billion years ago, nothing has changed, the earth goes through warmings and coolings. Just because we are in a warm interglacial is not proof that its caused by anthropogenic CO2 nor is it proof that the warming is bad on the contrary its good as not much life exists when its cold like during an ice age or are you going to try to tell us that cooling and a cold climate would be better? I don't think you will Susan will you? Or are you that silly?
    Old Crow
    2/02/2015 11:50:55 AM

    Keep worrying, Susan.
    Susan
    2/02/2015 8:28:52 AM

    Bill, Gumtree, Daw and Old Crow - as I posted earlier I just wanted to make the point here that global warming was continuing. I did not need or want to get involved in the matter of long term possibilities re. climate. From your posts it is clear that you don't understand that most of the increase in global CO2 is anthropogenic CO2 in origin - that amount can be worked out from the level of radioactive C (viz C13) present. Are you able to accept that the globe is still warming and make a statement to that effect here? I worry that you are just unable to do that.
    Gumtree
    2/02/2015 8:09:09 AM

    A TYPO and that should say "accepts " in my last post.
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