Study: natural variation still rules monsoons

From the University of Hawaii ‑ SOEST

Natural climate swings contribute more to increased monsoon rainfall than global warming

This is a three-layered cloud structure in a developing Madden-Julian Oscillation during the Indian Ocean DYNAMO field experiments (November 2011). The photo won first place in the DYNAMO photo contest. Credit: Owen Shieh, University of Hawaii

Natural swings in the climate have significantly intensified Northern Hemisphere monsoon rainfall, showing that these swings must be taken into account for climate predictions in the coming decades. The findings are published in the March 18 online publication of the Proceedings of the National Academy of Sciences.

Monsoon rainfall in the Northern Hemisphere impacts about 60% of the World population in Southeast Asia, West Africa and North America. Given the possible impacts of global warming, solid predictions of monsoon rainfall for the next decades are important for infrastructure planning and sustainable economic development. Such predictions, however, are very complex because they require not only pinning down how manmade greenhouse gas emissions will impact the monsoons and monsoon rainfall, but also a knowledge of natural long-term climate swings, about which little is known so far.

To tackle this problem an international team of scientists around Meteorology Professor Bin Wang at the International Pacific Research Center, University of Hawaii at Manoa, examined climate data to see what happened in the Northern Hemisphere during the last three decades, a time during which the global-mean surface-air temperature rose by about 0.4°C. Current theory predicts that the Northern Hemisphere summer monsoon circulation should weaken under anthropogenic global warming.

Wang and his colleagues, however, found that over the past 30 years, the summer monsoon circulation, as well as the Hadley and Walker circulations, have all substantially intensified. This intensification has resulted in significantly greater global summer monsoon rainfall in the Northern Hemisphere than predicted from greenhouse-gas-induced warming alone: namely a 9.5% increase, compared to the anthropogenic predicted contribution of 2.6% per degree of global warming.

Most of the recent intensification is attributable to a cooling of the eastern Pacific that began in 1998. This cooling is the result of natural long-term swings in ocean surface temperatures, particularly swings in the Interdecadal Pacific Oscillation or mega-El Niño-Southern Oscillation, which has lately been in a mega-La Niña or cool phase. Another natural climate swing, called the Atlantic Multidecadal Oscillation, also contributes to the intensification of monsoon rainfall.

“These natural swings in the climate system must be understood in order to make realistic predictions of monsoon rainfall and of other climate features in the coming decades,” says Wang. “We must be able to determine the relative contributions of greenhouse-gas emissions and of long-term natural swings to future climate change.”

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Citation: Bin Wang, Jian Liu, Hyung-Jin Kim, Peter J. Webster, So-Young Yim, and Baoqiang Xiang: Northern Hemisphere summer monsoon intensified by mega-El Niño/southern oscillation and Atlantic multidecadal oscillation. PNAS 2013; published ahead of print March 18, 2013, doi:10.1073/pnas.1219405110.

Funding for this work: B.W., S.-Y.Y., and B.X. acknowledge support from the International Pacific Research Center (IPRC) institutional support (JAMSTEC, NASA, and NOAA), Scientific Research Project of China Awards 2010CB950102 and XDA05080800 (to J.L. and B.W.), Korean Ministry of Education, Science and Technology Grant 2011-0021927 through Global Research Laboratory Program (to B.W.), National Science Foundation Awards AGS-1005599 (to B.W.) and ATM- 0965610 (to P.J.W.), Asian–Pacific Economic Cooperation Climate Center (B.X.), and the Program for Risk Information on Climate Change of Ministry of Education, Culture, Sports, Science and Technology, Japan (H.-J.K.).

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20 thoughts on “Study: natural variation still rules monsoons

  1. Is this surprising?

    Here’s what the AR4 says:

    “An increase in precipitation is projected in the Asian monsoon (along with an increase in interannual season-averaged precipitation variability) and the southern part of the west African monsoon with some decrease in the Sahel in northern summer, as well as an increase in the Australian monsoon in southern summer in a warmer climate. The monsoonal precipitation in Mexico and Central America is projected to decrease in association with increasing precipitation over the eastern equatorial Pacific through Walker Circulation and local Hadley Circulation changes. However, the uncertain role of aerosols in general, and carbon aerosols in particular, complicates the nature of future projections of monsoon precipitation, particularly in the Asian monsoon.”

  2. OOPS
    I’m sure if they spoke to Bob Tisdale he would be able to explain it to them. How the sea temp works to effect the weather. He has certainly explained it in a way I can get my head around, for which I thank him.
    James Bull

  3. “We must be able to determine the relative contributions of greenhouse-gas emissions and of long-term natural swings to future climate change.”

    No ****, Sherlock.

    The cooling of the Pacific that they refer to began when the jets and climate zones began to shift equatorward and become more meridional as the intensitry of solar activity declined from the peak of cycle 23.

    The change in solar activity altered atmospheric chemistry in the way I described some years ago to change the gradient of tropopause height between poles and equator.

    More clouds formed along the increased length of the lines of air mass mixing and less energy entered the oceans to fuel the climate system.

    At the same time the polar vortices became less vigorous vertically but spread out more across the surface with more outbreaks of cold air across middle latitudes.

    The advance of cooler air equatorward has increased temperature contrasts across the monsoonal regions to increase activity over the past 13 years or so.

    Prior to that the monsoons had been intensified by the high level of solar activity of the late 20th century causing less cloudiness and more energy into the oceans to fuel the climate system from the equator poleward hence the observation of poleward shifting jets and climate zones at that time.

    Interestingly, both a quiet sun and an active sun will intensify the monsoons if they succeed each other suddenly. The monsoons become less intense when there is a lengthy period of relatively stable solar activity.

    Change towards cooling or towards warming will always increase temperature differentials and intensify the monsoons and the faster the changes the more the intensity will increase.

    We have just shifted from a period of relatively rapid solar induced warming to a sudden halt and most likely soon a rapid solar induced cooling so we have the residual warmth from the earlier period coming up hard against the developing cooling from the current scenario.

    Looks like a bumpy ride for a while.

  4. 9.5 in data 2.6 in model, thus sensitivity has to be adjusted upwards to fit model. Reality cannot escape /sarc

  5. Stephen Wilde says: “The cooling of the Pacific that they refer to began when the jets and climate zones began to shift equatorward and become more meridional as the intensitry of solar activity declined from the peak of cycle 23.”

    The article reads, “Most of the recent intensification is attributable to a cooling of the eastern Pacific that began in 1998.”

    And the data says:

    The Eastern Pacific hasn’t warmed in 31 years. The “cooling” they’re referring to is simply an end to strong El Nino events and an increase in the frequencies of La Nina events, according to the data.

  6. The quotation from Prof. Wang in the last paragraph of the post says it all, really.
    Pity The Warmists don’t see it that way.
    (Funny, my spellchecker doesn’t like the word “warmists”.)

  7. Bob Tisdale said:

    “The “cooling” they’re referring to is simply an end to strong El Nino events and an increase in the frequencies of La Nina events, according to the data.”

    I agree, in part, but I think that the change in global cloudiness with less energy entering the oceans will enhance the change which you mention namely from a positive Pacific Multidecadal Oscillation (PMO not PDO) to a negative PMO.

    Over multidecadal periods of time I judge that variations in solar activity skew the balance between El Nino and La Nina events by changing the amount of energy entering the oceans to fuel the ENSO process.

    When did the PMO shift from positive to negative ?

    Was that in 1998 or somewhat later ?

  8. That could be interpreted as a rise for 15 years then a fall for 15 years leaving it flat overall.

    The point that I tried to address was why should the monsoon have intensified both during the rise and during the fall.

    It is a matter of the effect on temperature differentials (vertically and horizontally) caused by the competing effects of the sun operating from the poles and the oceans operating from the equator.

  9. Hi Anthony,

    This is a “headline alert”. Your headline can be interpreted as “Natural variations rule monsoons but do not rule climate change” which is hardly what I think you intended. Perhaps just leave off the “not climate change”? Or any of the other various ways of modifying the headline.

    I’m rereading the Fletch novels and hence am currently sensitive to the myriad ways of writing headlines so they have accidental antipodal meanings…;-)

    rgb

    REPLY: Yes, reading it now, you are correct. The intent was to say “not ruled by”. IIRC I was interrupted by a phone call when I posted this story. – I’ll fix. -Anthony

  10. Stephen Wilde says:
    March 21, 2013 at 2:31 am
    The cooling of the Pacific that they refer to began when the jets and climate zones began to shift equatorward and become more meridional as the intensity of solar activity declined from the peak of cycle 23.
    The amount of energy that the Earth receives from the Sun has not declined. In fact, is now higher than it was at the peak of cycle 23.

  11. What warming?
    When?
    When is the IPCC and its sycophants going to realize or acknowledge we live on a water dominant world?

  12. Nick Stokes says:
    March 21, 2013 at 12:28 am

    So, you want to give AR4 credit for the position stated in the article under discussion? To do so, you really need to make a comparison of specific claims. For example, the authors of this article write:

    “Such predictions, however, are very complex because they require not only pinning down how manmade greenhouse gas emissions will impact the monsoons and monsoon rainfall, but also a knowledge of natural long-term climate swings, about which little is known so far.”

    Does AR4 assert that scientists must go beyond the impact of greenhouse gases and develop a science that comprehends natural long-term climate swings? In other words, does AR4 actually emphasize the importance of natural regularities that are yet unknown?

    I doubt it. In fact, I would wager that an appreciation of the importance of a science of natural climate regularities would have precluded the scare mongering that has come from the IPCC. As the authors of this article imply, that science is in its infancy. And that science remains neglected by the lead authors of IPCC reports.

  13. There are some things I should know and somethings I don’t know, but should know. Then there are the obvious tidbits of climate I have always known, long before the reign of the doom and gloom drama queens and watermelons. This is something I knew as a nose picking kid. So much for the state of science these days.
    I’m still picking my nose in secret!

  14. Leif Svalgaard said:

    “The amount of energy that the Earth receives from the Sun has not declined. In fact, is now higher than it was at the peak of cycle 23.”

    Since you know full well that the relevant solar factors are not related to simple TSI I have to assume that your comment is designed to mislead readers who are not familiar with earlier discussions.

  15. “As for the Walker circulation and other niceties… Leroux finished them off a long time ago.”

    I don’t think he said much about causation and long term variability did he ?

  16. It seems to me the article is saying that natural variation buries AGW affects. I’ve heard this before from AGW proponents who are respected members of the research community.

  17. Stephen, he showed the so called Walker circulation was contradicted by data over west Africa for instance. As for long term variations of monsoons, they are deduced as logical consequences of the modes of circulation, rapid or slow.
    Dynamic Analysis of Weather and Climate, 2nd Ed. Springer 2010

  18. Natural variation is real, and proven. Emissions and global (anthropogenic) climate effects, not so much. In fact, not at all. Slipping it in as a presumption and assumption is scientifically despicable. And renders the article irrelevant, right from the get-go.

  19. Nick Stokes says:
    March 21, 2013 at 12:28 am

    Is this surprising?

    Here’s what the AR4 says:

    “An increase in precipitation is projected in the Asian monsoon (along with an increase in interannual season-averaged precipitation variability) and the southern part of the west African monsoon with some decrease in the Sahel……………..

    Is this surprising?

    [The following is a selection of peer reviewed research]
    East Africa to get less rain
    East Africa to get more rain [pdf]

    Indian monsoons to be drier
    Indian monsoons to be wetter

    Sahel to get less rain
    Sahel to get more rain
    Sahel may get more or less rain

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