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  • Review Article
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Southern Annular Mode dynamics, projections and impacts in a changing climate

Nature Reviews Earth & Environment volume 7, pages 24–42 (2026)Cite this article

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Abstract

The Southern Annular Mode (SAM) influences Southern Hemisphere temperature and precipitation, ocean circulation, carbon cycling and the Antarctic cryosphere. In this Review, we examine the dynamics, projections and effects of the SAM, focusing on future implications for the Southern Ocean and Antarctica. The SAM is the leading mode of atmospheric variability in the Southern Hemisphere extratropics, associated with variations in the mid-latitude westerly jet strength and position. The SAM is primarily an internally driven atmospheric process, for which anomalies dissipate in 1–2 weeks; however, sustained SAM anomalies can also be forced by stratospheric processes and tropical Pacific variability. Ozone depletion during the 1970s–1990s contributed to large positive trends in austral summer. The SAM is now in its most positive mean state in over 1,000 years, and a year-round positive trend in the SAM is projected to continue throughout the twenty-first century in response to increasing greenhouse gases. Given the importance of SAM effects on Southern Ocean circulation, carbon cycling, and Antarctic ice mass balance for future climate and sea level rise projections, it is crucial that the effects of SAM are better modelled and understood, including accounting for the influence of the shifting seasonality of positive SAM trends and its increasing asymmetry.

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Fig. 1: Zonal-mean and surface anomalies associated with positive SAM and time series.
Fig. 2: Seasonal 300-hPa zonal wind for positive and negative SAM, and the differences.
Fig. 3: Symmetric and asymmetric components of the SAM and relationships with drivers.
Fig. 4: Past, present and future evolution of the SAM.
Fig. 5: Historical SAM trend attribution.
Fig. 6: Seasonal surface impacts of the SAM.
Fig. 7: Key physical and biogeochemical impacts of SAM.

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Data availability

Figures 1–6 were made using data from ERA5 (ref. 197), which is available at https://www.ecmwf.int/en/forecasts/dataset/ecmwf-reanalysis-v5. Figures 1c and 4b used the Marshall SAM index4, which is available at http://www.nerc-bas.ac.uk/icd/gjma/sam.html. Figure 1c also used the US National Oceanographic and Atmospheric Administration Antarctic Oscillation198, which is available at https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/aao.shtml. Figures 4 and 5 were made using CMIP6 data198 available from the Earth System Grid Federation https://aims2.llnl.gov/search. Figure 4a was also made using data from the Paleoclimate Modelling Intercomparison Project phase 3 data199, which is also available from the Earth System Grid Federation. Figure 4c was made using data from ACCESS-ESM1.5 emissions-driven runs76, with data available at https://doi.org/10.5281/zenodo.17364274. Figure 5e,f was made using data from the National Snow and Ice Data Center Climate Data Record version 4 sea ice concentration200, available from https://nsidc.org/data/g02202/versions/4.

Code availability

Analysis code to reproduce Figs. 1–6 is available via Zenodo at https://doi.org/10.5281/zenodo.17393582.

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Acknowledgements

The initial draft for this manuscript was written at a workshop held in Melbourne in May 2024, funded by the United States Office of Naval Research Global (N62909-23-1-2097). This work was supported by the Australian Research Council, including the Special Research Initiative for Securing Antarctica’s Environmental Future (SR200100005), the Special Research Initiative Australian Centre for Excellence in Antarctic Science (SR200100008), the Centre of Excellence for Climate Extremes (CE17010023), the Centre of Excellence for Weather of the 21st Century (CE230100012), Discovery Projects DP230102994 and DP190100494, Discovery Early Career Research Award DE200100414, and Future Fellowship FT190100413, funded by the Australian Government. This project also received grant funding from the Australian Government as part of the Antarctic Science Collaboration Initiative programme (ASCI000002), the National Environmental Science Program and the Victorian Government’s Water and Climate Initiative. This research was undertaken with the assistance of resources and services from the National Computational Infrastructure, which is supported by the Australian Government. The authors thank S. McCormack for the assistance preparing Fig. 7. The authors also thank C. Chung, D. Jakob and D. Jones for their comments on the paper.

Author information

Authors and Affiliations

  1. School of Earth, Atmosphere and Environment, Monash University, Clayton, Kulin Nations, Victoria, Australia

    Ariaan Purich, Julie M. Arblaster, Elio Campitelli & Raina Roy

  2. ARC Special Research Initiative for Securing Antarctica’s Environmental Future, Clayton, Kulin Nations, Victoria, Australia

    Ariaan Purich, Julie M. Arblaster, Elio Campitelli & Raina Roy

  3. ARC Centre of Excellence for Climate Extremes, Eora Nation, Sydney, New South Wales, Australia

    Julie M. Arblaster, Ghyslaine Boschat, Zoe E. Gillett, Andrew King, Amelie Meyer, Valentina Ortiz Guzmán & Peter G. Strutton

  4. Research Bureau of Meteorology, Melbourne, Kulin Nations, Victoria, Australia

    Ghyslaine Boschat, Zoe E. Gillett, Eun-Pa Lim, Danielle Udy & Irina Rudeva

  5. Institute for Marine and Antarctic Studies, University of Tasmania, nipaluna/Hobart, Tasmania, Australia

    Will Hobbs, Danielle Udy, Edward Doddridge, Amelie Meyer, Paul Spence & Peter G. Strutton

  6. Australian Antarctic Program Partnership, nipaluna/Hobart, Tasmania, Australia

    Will Hobbs, Danielle Udy, Edward Doddridge & Amelie Meyer

  7. Climate Change Research Centre, University of New South Wales, Eora Nation, Sydney, New South Wales, Australia

    Martin Jucker, Laurie Menviel & Valentina Ortiz Guzmán

  8. ARC Australian Centre for Excellence in Antarctic Science, nipaluna/Hobart, Tasmania, Australia

    Danielle Udy, Nerilie Abram, Laurie Menviel, Amelie Meyer, Paul Spence & Peter G. Strutton

  9. Research School of Earth Sciences, Australian National University, Ngunnawal and Ngambri Country, Canberra, Australian Capital Territory, Australia

    Nerilie Abram

  10. Centre for Marine Science and Innovation and ARC Australian Centre for Excellence in Antarctic Science, University of New South Wales, Eora Nation, Sydney, New South Wales, Australia

    Matthew H. England

  11. School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Parkville, Kulin Nations, Victoria, Australia

    Andrew King

  12. ARC Centre of Excellence for the Weather of the 21st Century, nipaluna/Hobart, Tasmania, Australia

    Paul Spence

  13. CSIRO Environment, Aspendale, Kulin Nations, Victoria, Australia

    Tilo Ziehn

Authors
  1. Ariaan Purich
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  2. Julie M. Arblaster
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  3. Ghyslaine Boschat
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  4. Zoe E. Gillett
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  5. Will Hobbs
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  6. Martin Jucker
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  7. Eun-Pa Lim
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  8. Danielle Udy
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  9. Nerilie Abram
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Contributions

A.P., J.M.A., M.H.E., M.J. and E.-P.L. conceived the Review. A.P. organized the writing workshop and led the overall coordination of the paper. Z.E.G. led the dynamics section, J.M.A. led the trends and projections section, and W.H. led the impacts section. G.B. prepared Figs. 1,4 and 5, M.J. prepared Fig. 2, V.G.O. prepared Fig. 3, R.R. prepared Fig. 6, and W.H. and A.P. designed Fig. 7. All authors wrote the initial manuscript, reviewed, edited and improved the paper.

Corresponding author

Correspondence to Ariaan Purich.

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The authors declare no competing interests.

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Nature Reviews Earth & Environment thanks Deborah Verfaillie, Xiaoqiao Wang, Zhaoru Zhang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Glossary

Amundsen Sea Low

A climatological persistent low-pressure centre located in the Pacific sector of the Southern Ocean off the coast of West Antarctica, over the Amundsen and Bellingshausen seas.

Antarctic Bottom Water

A cold, dense water mass formed near Antarctica from dense shelf water that sinks and spreads along the ocean floor into the deepest parts of the global ocean; it has a key role in global meridional ocean circulation and climate regulation.

Antarctic Circumpolar Current

A major eastwards-flowing ocean current that encircles Antarctica, connecting the Atlantic, Indian and Pacific oceans, thereby facilitating the global exchange of heat, freshwater and nutrients.

Antarctic Slope Current

A high-latitude westwards-flowing current on the edge of the Antarctic continental shelf that encircles most of the continent and forms a boundary between the open ocean and continental shelf waters, regulating the transport of water towards the continent.

Antarctic stratospheric vortex

A band of strong winds blowing from the west to the east, encircling the mid-latitude to sub-Antarctic region in the stratosphere (~10–55 km altitudes), typically present from austral late autumn to late spring.

Anthropogenic carbon

Carbon within the atmospheric, oceanic or terrestrial realm that is of anthropogenic origin.

Chlorophyll

The photosynthetic pigment contained in land plants and ocean phytoplankton, used here as a proxy for phytoplankton abundance and, approximately, ocean productivity.

Circumpolar Deep Water

A water mass that upwells to the near surface of the polar and subpolar Southern Ocean, consisting of a blend of deep water masses from the Atlantic, Indian and Pacific ocean basins, with about half sourced from North Atlantic deep water.

Coupled Model Intercomparison Project phase 6

(CMIP6). The internationally coordinated set of defined climate model experiments and shared model outputs from modelling groups around the world.

Dense shelf water

A dense water mass formed on the Antarctic continental shelf through sea ice production whose temperature is therefore the local freezing temperature and its density is set by its salinity.

Dissolved inorganic carbon

The sum of bicarbonate (HCO3−) and carbonate (CO32) ions, plus aqueous CO2 (CO2(aq)), also referred to as carbonic acid, H2CO3.

Eddy

A transient disturbance that deviates from the mean flow in the atmosphere or ocean (includes cyclones and anticyclones in the atmosphere).

Eddy momentum flux convergence

The net transfer of zonal momentum from atmospheric eddies into the mean flow, resulting in westerly acceleration of the zonal-mean flow caused by the propagation of waves away from their source region.

Eddy momentum flux divergence

The net removal of zonal momentum from the mean flow by atmospheric eddies, corresponding to deceleration of the zonal-mean flow due to breaking waves.

Ekman transport

Also termed Ekman drift; a wind-driven flow of water in the upper surface layer of the ocean resulting from a combination of wind drag and the Coriolis effect, which deflects the flow to the left of the wind in the Southern Hemisphere, and to the right of the wind in the Northern Hemisphere.

El Niño Southern Oscillation

(ENSO). A naturally occurring fluctuation in sea surface temperatures coupled with winds and pressure across the tropical Pacific Ocean, associated with sustained warming (El Niño) or cooling (La Niña) in the central and eastern tropical Pacific, typically occurring every 2–7 years.

Ferrel cell

The mid-latitude component of the extratropical mean meridional circulation, consisting of poleward flow near the surface, upwards motion near the mid-latitude jet, equatorward flow aloft and subsidence in the subtropics.

Hadley circulation

Also termed Hadley cell; the thermally driven mean meridional circulation characterized by rising warm, moist air in the tropics; poleward motion aloft; sinking cooler, drier air in the subtropics; and equatorward flow at the surface, transporting energy, momentum and moisture between these regions.

Interdecadal Pacific Oscillation

A naturally occurring decadal-to-multidecadal fluctuation of Pacific sea surface temperatures, coupled with atmospheric circulation, with a spatial pattern resembling ENSO but extending into the extratropical Pacific.

Madden–Julian Oscillation

A pulse of tropical convective activity (cloud and rainfall) that propagates eastwards near the equator, from the Indian Ocean to the western Pacific Ocean, with a cycle repeating approximately every 30–60 days.

Mid-latitude eddy-driven jet

A band of strong westerly winds extending from the surface to the upper troposphere in the mid-to-high latitudes of both hemispheres, driven by eddy momentum flux convergence. Unlike the subtropical jet, the mid-latitude eddy-driven jet arises from the cumulative effect of eddies rather than a coherent flow.

Natural carbon

Carbon within the atmosphere, oceanic or terrestrial realm that has not been affected by anthropogenic emissions of carbon, considered equivalent to pre-industrial carbon.

Net-zero emissions

The balance of anthropogenic carbon dioxide emissions with equivalent uptake of carbon from the atmosphere through anthropogenic activities (sometimes net-zero emissions are used to refer to all greenhouse gases rather than just carbon dioxide).

Pacific–South American pattern

A Rossby wave train that extends from the central Pacific Ocean to the Amundsen and Weddell seas, manifesting across intraseasonal to decadal timescales.

Rossby waves

Large-scale (planetary) or synoptic-scale waves in the atmosphere that arise from the variation of the Coriolis effect with latitude.

Subtropical jet

A band of strong westerly winds located in the upper troposphere of the subtropics on the poleward side of the Hadley cell of both hemispheres, peaking in winter.

Surface mass balance

The net effect of ice sheet mass gain due to precipitation, and mass loss primarily by temperature-driven surface melt.

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Purich, A., Arblaster, J.M., Boschat, G. et al. Southern Annular Mode dynamics, projections and impacts in a changing climate. Nat Rev Earth Environ 7, 24–42 (2026). https://doi.org/10.1038/s43017-025-00746-y

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