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

    Gumtree
    2/02/2015 7:41:35 AM

    And Nico chooses to ignore known history which the entire world excepts as fact.
    nico
    2/02/2015 7:17:47 AM

    If you accept Carter as a climate science reference, daw, you need to read more widely. But Carter's political associations are significant: eg the Heartland Institute, the IPA. These are right-wing political groups which no scientist should touch with a delingpole - not because they dispute climate science but because they are anti-science itself. I stand corrected on Carter as a mining geologist. (It was ocean drilling) but Carter seems to given up science for advocacy. Plimer is the mining geologist. I have given Gummy scientific references, which he ignores.
    Gumtree
    2/02/2015 6:32:44 AM

    BP, do try to be patient with Susan, after all the AGW crowd don't believe in history past 100 years ago so she would have no idea about the last ice age and sea level rise since then. Basically the AGW crowd are ignorant with their heads encased in concrete and impervious to any education at all.
    Old Crow
    31/01/2015 8:05:30 AM

    Susan and Oliver join Nico in confirming how out of touch they really are.
    daw
    30/01/2015 6:46:40 PM

    YES Nico Laws of motion! I'm not explaining them to you here. Your'e getting desperate now. Carter refutes the claim re Heartland Inst below the cartoon ( pp62). You fail to give ref to 'reviewed by genuine climate scientists' Perhaps they agree with him like his co authors do. Review by Skepticalscience Ian Enting pfffft. See Carter et al's response. ref. www.taxingair.com/review-response s-ian-enting.html I'm as interested as Gumtree to see your answer to his question. By the way he is not and never has been a mining geologist! Do try harder to get a few things right.
    Bill Pounder
    30/01/2015 6:10:33 PM

    Susan, there is no mystery at all regarding sea levels, how's 130 metres rise over 20,000 years sound. There was no Great Barrier Reef, Queensland's continental shelf was a coastal plain & rivers met the sea about 160 kms further east. http://digitalcommons.unl.edu/geo sciencefacpub/386/ Then, voilà, crazy melting started around 14,000 years ago & peaked about 1,000 years ago in the MWP. All this when there were no SUVs or A/C units or people in high rise. So get a grip, there are bigger forces at play & one of them is as oceans warm CO2 is released, which explains most of the increase seen.
    Susan
    30/01/2015 10:15:03 AM

    hi Bushie - the only point I want to make here is that claims that global warming has ceased are wrong . As long as global sea level continues to rise , as it has continued to do over the last 18 years , there must be global warming going on - no alternative explanation exists. Climate scientists are active in studying where in the ocean the extra heat is going - google "Mystery of Ocean Heat Deepens as Climate Changes".
    nico
    30/01/2015 6:19:32 AM

    Semantics, daw. Not worth arguing about. It is the nature of science to observe facts, propound a theory to account for the facts, and make predictions based on the facts. The fact in this case is that the graph of measured global temperature is going up. The prediction, (conjecture if you like, though a scientist would not use the word) is that it will continue to do so (unless there is an unexpected event such an an eruption.)
    Bill Pounder
    29/01/2015 7:50:51 PM

    Sheesh, Susan, where'd you dredge up that pile of ... Sure atmospheric CO2 has been increasing, however satellite temperature data (RSS, an accepted & unadultered set) shows no warming for 18+ years. Therefore, it is reasonable to conclude that the known logarithmic warming effect of CO2 in the atmosphere is pretty well "tuckered out". Meanwhile, cast your mind back to 1850 & recall that any warming since then can be easily attributed to the ending of the Little Ice Age, which, of course, was preceded by the Mediaeval Warm Period. So, yawn, sea levels have been increasing for 20,000 years.
    Oliver
    29/01/2015 4:55:09 PM

    Susan seems to have smoked out more yesterday's men viz. Old Crow & Gum Tree . They claim no global warming. They do this despite the fact that global sea level has continued to rise steadily even over the last 18yr. Those rises are due to global warming something the yesterday's men can't handle . Atmospheric temperature has failed to increase during periods of decades in the last 140 yr but the long term increase still prevails. For some reason more heat goes into the oceans at various times and this reduces the rate of atmospheric warming but the overall global warming continues.
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