Southern Hemisphere Climate Dynamics and Variability

The climate of the Southern Hemisphere is shaped by unique atmospheric circulation modes, ocean–atmosphere interactions and external forcings. The Southern Annular Mode (SAM) governs the strength and latitudinal position of mid-latitude westerlies, influencing Southern Ocean currents, sea-ice distribution and continental precipitation. Variations in the SAM interact with tropical phenomena such as the El Niño–Southern Oscillation, producing teleconnections that modulate regional rainfall, marine productivity and glacial mass balance. The stratospheric ozone hole has driven a poleward shift and intensification of westerly jets since the late twentieth century, while anthropogenic greenhouse gas forcing is projected to further modify jet dynamics, precipitation patterns and ocean circulation. Recent improvements in climate models have reduced biases in jet latitude and variability, enhancing confidence in future scenarios. Palaeoclimate reconstructions reveal that modern trends in atmospheric modes lie outside the range of natural variability, underlining the role of human influence. Such dynamics have profound implications for global heat and carbon uptake, Antarctic ice stability and socio-ecological systems across Australasia, South America and the Southern Ocean islands.

Research from Nature Portfolio

Recent studies have reconstructed two millennia of SAM variability using data assimilation and multi-proxy climate archives, demonstrating that the modern positive trend in the SAM at multidecadal scales exceeds natural fluctuations observed over the Common Era and is attributable to anthropogenic forcing. Other work has unveiled an atmospheric origin for the bipolar seesaw, linking interhemispheric surface temperature contrasts to changes in Southern Hemisphere westerly winds driven by tropical and Northern Hemisphere tropospheric warming, independently of ocean circulation variations.

Southern Hemisphere Climate Dynamics and Variability publication trend

The graph below shows the total number of articles in southern hemisphere climate dynamics and variability across all publications each year (not limited to Nature Index journals).

Technical terms

Southern Annular Mode: The principal pattern of extratropical variability in the Southern Hemisphere, defined by pressure differences between mid and high latitudes that govern the strength and position of westerly winds.

Westerly winds: Prevailing west-to-east winds encircling the Southern Hemisphere mid-latitudes, critical for ocean upwelling, heat transport and weather systems.

Mixed Layer Depth: The upper ocean layer homogenised by wind and wave mixing, which controls nutrient availability and surface temperature.

Bipolar seesaw: A pattern of opposing temperature trends between the Arctic and Antarctic, linked to shifts in atmospheric or oceanic circulation.

Meridional pressure gradient: The latitudinal change in atmospheric pressure that drives large-scale wind and ocean currents.

References

1. Trends and variability in the Southern Annular Mode over the Common Era. Nature Communications (2023).
2. Lagged effect of Southern Annular Mode on chlorophyll-a in the mid-latitude South Pacific and Indian Oceans. Environmental Research Letters (2024).
3. Tropospheric jet response to Antarctic ozone depletion: An update with Chemistry-Climate Model Initiative (CCMI) models. Environmental Research Letters (2018).
4. Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5. Earth and Space Science (2020).
5. An atmospheric origin of the multi-decadal bipolar seesaw. Scientific Reports (2015).
6. Teleconnections and relationship between the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) in reconstructions and models over the past millennium. Climate of the Past (2020).
7. Changes of Southern Hemisphere westerlies in the future warming climate. Atmospheric Research (2022).
8. Projected Changes of Surface Winds Over the Antarctic Continental Margin. Geophysical Research Letters (2022).