Understanding present and future dynamics of ENSO and the IOD

Dr Agus Santoso

Dr Guojian Wang

Project leaders: Drs Agus Santoso (CSIRO and UNSW) and Guojian Wang (CSIRO)

Staff: Drs Dave Bi and Benjamin Ng.


[Music plays and animation waves appear moving up from the bottom of the screen and text appears above: The Centre for Southern Hemisphere Oceans Research]

[Image shows animation waves moving up the screen and over the text and then the image changes to show Agus Santoso talking to the camera and text appears: Agus Santoso, CSHOR Project Leader, University of New South Wales]

Agus Santoso: The project I will be leading will be investigating the role of Southern Hemisphere oceans in the dynamics of El Nino and Indian Ocean Dipole.

[Image changes to show a view of the ocean from the deck of a research vessel and the camera pans to the left and then the image changes to show Agus talking to the camera]

Southern Ocean is a big question mark, so by understanding the role of southern oceans, then we will be able to improve things like prediction of El Nino Southern Oscillation and of course eventually it will benefit many people.

[Image changes to show a view looking over the bow of a ship moving through the ocean]

This work is important because tropical climate variability like El Nino and Indian Ocean Dipole impact on climate around the world such as countries like Australia.

[Image changes to show Ming Feng and Larry Marshall clapping as a plaque is unveiled and then shaking hands and then the image changes to show Agus talking to the camera]

CSHOR will benefit people in how we can manage resources and how we can manage doing flood management better in terms of anticipating all these impactful climate events in present day and in the future.

[Music plays and the image changes to show animation waves across the bottom of the screen and Qingdao National Laboratory for Marine Science and Technology, CSIRO, UNSW and University of Tasmania logos appear]

Dr Agus Santoso introducing the ENSO/IOD project

Project objectives

The El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) affect millions of human lives in the tropical belt and beyond. The likelihood of extreme weather events such as drought, heatwaves, floods, and cyclones is elevated during such events, particularly extreme ENSO and extreme positive IOD. Understanding their dynamics is of utmost importance as to enhance our capacity to predict their occurrences, especially their trends in a climate that is undergoing change.

Present outstanding issues on this topics are many, and these include: generation mechanism of ENSO diversity (mechanism of extreme El Niño and weak El Niño) and the associated diversity in ENSO teleconnections; uncertainty in projected change in future ENSO and the IOD; and the role of the Southern Hemisphere oceans, in the ENSO and the IOD life cycle.

The objectives of the project are to:

  • understand how ENSO and IOD events are generated, in particular, how they attain extreme amplitude, how they interact with each other and with the Southern Hemisphere oceans
  • examine the causes for decadal modulation of ENSO and IOD characteristics, and the potential role of Southern Hemisphere oceans
  • project changes in ENSO and the IOD under greenhouse warming, as well as their interactions and teleconnection, and assess uncertainty in the projected change.

Latest news

Dr Guojian Wang’s science journey

14 April 2021

Dr Guojian Wang from the CSHOR team has shared a story on his science journey with the CSIRO blog. Read more about Guojian’s research into El Nino Southern Oscillation and the Indian Ocean Dipole, and what inspired him into a science carer, at this link.

CSHOR Session at AMOS 2021

CSHOR project leaders, Guojian Wang, Agus Santoso, Xuebin Zhang and Benjamin Ng are convening a session titled, ‘Southern hemisphere oceans and climate variability‘ at the AMOS 2021 Conference – online from 8 to 12 February 2021. 

Abstract: The southern hemisphere oceans encompass many key elements of the Earth’s climate system, e.g., Indo-Pacific warm pool, Indonesian Throughflow, Super-gyre Circulation, and the vast Southern Ocean. Although more than 80% of the southern hemisphere is covered by ocean, the Amazonia, which has the largest rainforest in the world working as the lungs of the planet, and the Antarctic, which is covered by an average two-kilometre-thick ice sheet, can influence the Earth’s climate tremendously. All these components are influenced by climate variability in the region, including in the Indo-Pacific Oceans, such as the El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) which exert significant impact on weather patterns, rainfall, air-sea fluxes, sea level, ocean density and circulations, ecosystems, and many others. How these modes of variability teleconnect in the southern hemisphere, and how they change under global warming, continue to be areas of active research.

Abstracts close on 6 November 2020.

Visit the conference website at this link.

Opposite response of strong and moderate positive Indian Ocean Dipole to greenhouse warming

1 December 2020

A new study by Cai, Yang and Wu et al. published today in Nature Climate Change shows that climate extremes seen in 2019-20 are likely to occur more frequently under greenhouse warming. Faster warming in the equatorial northwestern Indian Ocean favours atmosphere convection in the region. Equatorial nonlinear positive feedbacks responsible for the strong cooling in the equatorial eastern Indian Ocean are strengthened. Low-tropospheric warming which is faster than the surface warming is inconducive to Ekman pumping that drives warm anomalies. For further detail and a link to the full article, go to the CSHOR post at this link.

Book Release – ENSO in a changing climate

Update – on 29 December 2020, the book,El Niño Southern Oscillation in a Changing Climate’, launched in November 2020, was highlighted in a Sydney Morning Herald article explaining El Niño and La Niña events.

November 2020

El Niño is an unusual warming of the tropical Pacific that wreaks havoc on weather systems around the globe.  It happens every few years and, like its cold counterpart La Niña, has profound effects on society and the environment.  The irregular cycle between warm El Niño and cold La Niña events, referred to as El Niño Southern Oscillation, or ENSO, is the focus of a new book, El Niño Southern Oscillation in a Changing Climate, published by Wiley as part of the centennial celebration of the American Geophysical Union. The book is the first comprehensive examination of how ENSO cycle dynamics and impacts may change under the influence of rising greenhouse gas concentrations in the atmosphere.

Michael McPhaden (U.S. National Oceanic and Atmospheric Administration (NOAA) and CSHOR Advisory Committee Member), Agus Santoso (University of New South Wales (UNSW) and CSHOR project leader), and Wenju Cai (CSIRO and CSHOR Director), served as editors of the book.

Read the Editors’ Vox on the Eos website at this link.

La Niña event expected in 2020/21

28 September 2020

Dr Agus Santoso was interviewed by Peter Hannam for the Sydney Morning Herald/The Age about an emerging La Niña in 2020. The article reports that the Bureau of Meteorology is expected to declare a La Niña event is under way in the Pacific, underscoring climate influences that point to a wetter than usual end to 2020 across northern and eastern Australia. The article is available here.

Butterfly effect and a self-modulating El Niño response to global warming

3 September 2020

In an article published online today in Nature we show that like a butterfly effect, an infinitesimal random perturbation to identical initial conditions induces vastly different initial ENSO variability, which systematically affects its response to greenhouse warming a century later. In experiments with higher initial variability, a greater cumulative oceanic heat loss from ENSO thermal damping reduces stratification of the upper equatorial Pacific Ocean, leading to a smaller increase in ENSO variability under subsquent greenhouse warming. This self-modulating mechanism operates in two large ensembles generated using two different models, each commencing from identical initial conditions but with a butterfly perturbation; it also operates in a large ensemble generated with another model commencing from different initial conditions and across climate models participating in the Coupled Model Intercomparison Project. Thus, if the greenhouse-warming-induced increase in ENSO variability is initially suppressed by internal variability, future ENSO variability is likely to be enhanced, and vice versa. This self-modulation linking ENSO variability across time presents a different perspective for understanding the dynamics of ENSO variability on multiple timescales in a changing climate. Go to the CSHOR post for a link to the article and to related news items.

CSHOR science seminar project presentation, July 2020


Abellán, E., McGregor, S., England, M. H., & Santoso, A. (2017). Distinctive role of ocean advection anomalies in the development of the extreme 2015–16 El Niño. Climate Dynamics. https://doi.org/10.1007/s00382-017-4007-0.

Bordbar, M. H., M. H. England, A. Sen Gupta, A. Santoso, A. S. Taschetto, T. Martin, W. Park, M. Latif (2019). Uncertainty in near-term global surface warming linked to tropical Pacific climate variability. Nature Communications, 10:1990. https://doi.org/10.1038/s41467-019-09761-2.

Cai, W., McPhaden, M. J., Grimm, A. M., Rodrigues, R. R., Taschetto, A. S., Garreaud, R. D., . . . Vera, C. (2020). Climate impacts of the El Niño–Southern Oscillation on South America. Nature Reviews Earth & Environment, 1(4), 215-231. https://doi.org/10.1038/s43017-020-0040-3.

Cai, W., Ng, B., Geng, T. Wu, L., Santoso, A., McPhaden, M. J. (2020). Butterfly effect and a self-modulating El Niño response to global warming. Nature, 58568–73. https://doi.org/10.1038/s41586-020-2641-x.

Cai, W., A. Santoso, G. Wang, L. Wu, M. Collins, M. Lengaigne, S. Power, and A. Timmermann (2020). Chapter 13: ENSO Response to Greenhouse Forcing. AGU Monograph: ENSO in a Changing Climate.  McPhaden, M., A. Santoso, W. Cai (Eds.), Wiley. https://doi.org/10.1002/9781119548164.ch13.

Cai, W., G. Wang, B. Dewitte, L. Wu, A. Santoso, K. Takahashi, Y. Yang, A. Carreric, and M. J. McPhaden (2018b). Increased variability of Eastern Pacific El Niño under greenhouse warming. Nature, 564, 201-206. https://doi.org/10.1038/s41586-018-0776-9.

Cai, W., Wang, G., Gan, B., Wu, L., Santoso, A., Lin, X., Chen, Z., Jia, F., & Yamagata, T. (2018). Stabilised frequency of extreme positive Indian Ocean Dipole under 1.5 °C warming. Nature Communications, 9(1), 1419. https://www.nature.com/articles/s41467-018-03789-6.

Cai, W., Wang, G., Santoso, A., Lin, X., & Wu, L. (2017). Definition of Extreme El Niño and Its Impact on Projected Increase in Extreme El Niño Frequency. Geophysical Research Letters, 44(21), 11,184-111,190. http://dx.doi.org/10.1002/2017GL075635.

Cai, W., Wu, L., Lengaigne, M. et al. (2019). Pantropical climate interactions. Science, 363(6430), eaav4236. http://science.sciencemag.org/content/363/6430/eaav4236.

Cai, W., Yang, K., Wu, L., Huang, G., Santoso, A., Ng, B., Wang, G. and Yamagata, T. (2021). Opposite response of strong and moderate positive Indian Ocean Dipole to global warming. Nature Climate Change, 11, 27–32. https://doi.org/10.1038/s41558-020-00943-1.

Geng, T., Cai, W., & Wu, L. (2020). Two types of ENSO varying in tandem facilitated by nonlinear atmospheric convection. Geophysical Research Letters, 47. https://doi.org/10.1029/2020GL088784.

Herold, N., & Santoso, A. (2017). Indian Ocean warming during peak El Niño cools surrounding land masses. Climate Dynamics. https://doi.org/10.1007/s00382-017-4001-6.

Holmes, R. M., McGregor, S., Santoso, A., & England, M. H. (2018). Contribution of Tropical Instability Waves to ENSO Irregularity. Climate Dynamics. https://doi.org/10.1007/s00382-018-4217-0.

Hu, S., Sprintall, J., Guan, C., McPhaden, M. J., Wang, F., Hu, D., & Cai, W. (2020). Deep-reaching acceleration of global mean ocean circulation over the past two decades. Science Advances, 6(6), eaax7727. https://doi.org/10.1126/sciadv.aax7727.

Jia, F., Cai, W., Wu, L., Gan, B., Wang, G., Kucharski, F., . . . Keenlyside, N. (2019). Weakening Atlantic Niño–Pacific connection under greenhouse warming. Science Advances, 5(8), eaax4111. https://advances.sciencemag.org/content/5/8/eaax4111?rss=1.

Jo. H.-S., Yeh S.-W., Cai W., 2019: An Episodic Weakening in the Boreal Spring SST–Precipitation Relationship in the Western Tropical Pacific since the Late 1990s, Journal of Climate, 32, 3837-3845. https://doi.org/10.1175/JCLI-D-17-0737.1.

Karamperidou, C., M. F. Stuecker, A. Timmermann, K.-S. Yun, S.-S. Lee, F.-F. Jin, A. Santoso, M. J. McPhaden, and W. Cai (2020).  Chapter 21: ENSO in a Changing Climate: Challenges, Paleo-Perspectives, and Outlook. AGU Monograph: ENSO in a Changing Climate. McPhaden, M., A. Santoso, W. Cai (Eds.), Wiley. https://doi.org/10.1002/9781119548164.ch21.

Li, S., L. Wu, Y. Yang, T. Geng, W. Cai, B. Gan, Z. Chen, Z. Jing, G. Wang, X. Ma (2020). The Pacific Decadal Oscillation less predictable under greenhouse warming. Nature Climate Change, 10, 30-34. https://doi.org/10.1038/s41558-019-0663-x.

Makarim, S., J. Sprintall, Z. Liu, W. Yu, A. Santoso, X.-H. Yan, R. D. Susanto (2019). Previously unidentified Indonesian Throughflow pathways and freshening in the Indian Ocean during recent decades. Scientific Reports, 9:7364. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6517581/.

McKenna, S., A. Santoso, A. Sen Gupta, A. Taschetto, W. Cai (2020). Indian Ocean Dipole in CMIP5 and CMIP6: Characteristics, biases, and links to ENSO.  Scientific Reports 10(1), 11500. https://doi.org/10.1038/s41598-020-68268-9.

McPhaden, M., A. Santoso, W. Cai (Eds.) (2020). El Niño Southern Oscillation in a Changing Climate, 528pp, Geophysical Monograph Series, Vol. 253, American Geophysical Union, John Wiley & Sons, Print ISBN:9781119548126. Online ISBN:9781119548164. https://agupubs.onlinelibrary.wiley.com/doi/book/10.1002/9781119548164.

McPhaden, M., A. Santoso, and W. Cai (2020). Chapter 1: Introduction to ENSO in a Changing Climate.  AGU Monograph: ENSO in a Changing Climate. McPhaden, M., A. Santoso, W. Cai (Eds.), Wiley. https://doi.org/10.1002/9781119548164.ch1.

Ng, B., Cai, W., Cowan, T., & Bi, D. (2021).   Impacts of Low-Frequency Internal Climate Variability and Greenhouse Warming on El Niño–Southern Oscillation, Journal of Climate, 34(6), 2205-2218.  https://journals.ametsoc.org/view/journals/clim/34/6/JCLI-D-20-0232.1.xml.

Santoso, A., Hendon, H., Watkins, A., et al. (2019a). Dynamics and predictability of the El Niño-Southern Oscillation: An Australian perspective on progress and challenges. Bulletin of the American Meteorological Society, 100, 403-420. https://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-18-0057.1.

Santoso, A., McPhaden, M. J., & Cai, W. (2017). The Defining Characteristics of ENSO Extremes and the Strong 2015/2016 El Niño. Reviews of Geophysics, 55(4), 1079-1129. https://doi.org/10.1002/2017RG000560.

Timmerman, A., An, S. I., Kug, J. S., Jin, F. F., & Cai, W., et al. (2018). El Niño-Southern Oscillation complexity. Nature, 559(7715), 535-545.  https://doi.org/10.1038/s41586-018-0252-6.

Wang, G., Cai, W. (2020). Two-year consecutive concurrences of positive Indian Ocean Dipole and Central Pacific El Niño preconditioned the 2019/2020 Australian “black summer” bushfires. Geoscience Letters, 7(1), 19. https://doi.org/10.1186/s40562-020-00168-2.

Wang, G. J., Cai, W. J., Gan, B. L., Wu, L. X., Santoso, A., Lin, X. P., Chen, Z. H., & McPhaden, M. J. (2017). Continued increase of extreme El Niño frequency long after 1.5 degrees C warming stabilization. Nature Climate Change, 7(8), 568-572. https://www.nature.com/articles/nclimate3351.

Wang, G. J., Cai, W. J., & Santoso, A. (2017). Assessing the Impact of Model Biases on the Projected Increase in Frequency of Extreme Positive Indian Ocean Dipole Events. Journal of Climate, 30(8), 2757-2767. http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0509.1.

Wang, G., W. Cai, A. Santoso (2019). Stronger increase in the frequency of extreme convective El Niño than extreme warm El Niño under greenhouse warming. Journal of Climate. https://doi.org/10.1175/JCLI-D-19-0376.1.

Wang, G., W. Cai, A. Santoso (2020). Stronger increase in the frequency of extreme convective El Niño than extreme warm El Niño under greenhouse warming. Journal of Climate, 33(2), 675-690. https://doi.org/10.1175/JCLI-D-19-0376.1.

Wang, G., Cai, W., & Santoso, A. (2021). Simulated thermocline tilt over the tropical Indian Ocean and its influence on future sea surface temperature variability. Geophysical Research Letters, 48, e2020GL091902. https://doi.org/10.1029/2020GL091902.

Wang, G., Cai, W., Yang, K., Santoso, A., & Yamagata T. (2020). A unique feature of the 2019 extreme positive Indian Ocean Dipole event. Geophysical Research Letters, 47. https://doi.org/10.1029/2020GL088615.

Yang, K., Cai, W., Huang, G., Wang, G., Ng, B., & Li, S. (2020). Oceanic processes in ocean temperature products key to a realistic presentation of positive Indian Ocean Dipole nonlinearity. Geophysical Research Letters, 46. https://doi.org/10.1029/2020GL089396.

Yang, K., Cai, W., Huang, G., Ng, B., & Wang, G. (2021). Is preconditioning effect on strong positive Indian Ocean Dipole by a preceding Central Pacific El Niño deterministic? Geophysical Research Letters, 48, e2020GL092223. https://doi.org/10.1029/2020GL092223.

Zhong, W. X., Zheng, X. T., & Cai, W. J. (2017). A decadal tropical Pacific condition unfavorable to central Pacific El Niño. Geophysical Research Letters, 44(15), 7919-7926. https://doi.org/10.1002/2017GL073846.