Disentangling Anthropogenic Effects on Southern Hemisphere Circulation and Surface Climate: A Multi‐Model Large Ensemble Approach

Abstract Southern Hemisphere (SH) circulation and surface climate changes are emerging in recent decades. For example, in most seasons, the SH Hadley cell edge and the eddy‐driven jet stream have shifted polewards, and the Southern Annular Mode (SAM) has trended towards its positive phase. However, attributing these changes to specific external forcings, such as greenhouse gas (GHG) increases or stratospheric ozone depletion, has been hindered by small ensemble sizes and lack of coherent forcing methodology across multiple models. In this study, we analyzed simulations from 10 models within the Large Ensemble Single Forcing Model Intercomparison Project (LESFMIP) to isolate the long‐term (1850–2014) SH climate response to individual forcings (GHGs, aerosols, and ozone). We found that long‐term SH climate trends are dominated by GHGs across all seasons. Over this time period, stratospheric ozone depletion exerts an influence comparable to GHGs but is restricted to austral spring and summer. Although anthropogenic aerosols show weaker effects on climate trends that oppose those induced by GHG forcing and ozone depletion, they have a noticeable impact. Notably, ozone recovery following the Montreal Protocol is currently weakening or reversing spring and summer trends in key circulation metrics. Finally, we quantify the degree to which the observed sea surface cooling of the Southern Ocean and Antarctic sea ice increase from 1980 to 2014 fall outside the models' ensemble spread. Our results highlight the need to better understand the roles of different forcings, model differences, and discrepancies between models and observations to constrain projections of future Southern Hemisphere climate change.

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Publication Details

Journal
Journal of Geophysical Research Atmospheres
Published
2026-08-19
DOI
https://doi.org/10.1029/2025jd046229
Primary Topic
Climate variability and models
Type
article
Field-Weighted Citation Impact
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article

Disentangling Anthropogenic Effects on Southern Hemisphere Circulation and Surface Climate: A Multi‐Model Large Ensemble Approach

Scott Osprey, W. Dow, Doug Smith, Michael Sigmond et al.
Journal of Geophysical Research Atmospheres
Climate variability and models
article

Disentangling Anthropogenic Effects on Southern Hemisphere Circulation and Surface Climate: A Multi‐Model Large Ensemble Approach

Scott Osprey, W. Dow, Doug Smith, Michael Sigmond, Yuanrui Chen, Eun‐Pa Lim, Amanda C. Maycock, Tiffany A. Shaw, Julia Mindlin, Thomas J. Bracegirdle, H. Khatri, J. Mindlin, C Boehm, J. Arblaster, L. Diaz, C. Garfinkel, D. Avisar, J. Wright, B. Mezzina, G. Boschat, E. Behrens, A. Butler, K. Grise, S. Bischof, P. Athanasiadis, M. Osman
article en

Abstract

Abstract Southern Hemisphere (SH) circulation and surface climate changes are emerging in recent decades. For example, in most seasons, the SH Hadley cell edge and the eddy‐driven jet stream have shifted polewards, and the Southern Annular Mode (SAM) has trended towards its positive phase. However, attributing these changes to specific external forcings, such as greenhouse gas (GHG) increases or stratospheric ozone depletion, has been hindered by small ensemble sizes and lack of coherent forcing methodology across multiple models. In this study, we analyzed simulations from 10 models within the Large Ensemble Single Forcing Model Intercomparison Project (LESFMIP) to isolate the long‐term (1850–2014) SH climate response to individual forcings (GHGs, aerosols, and ozone). We found that long‐term SH climate trends are dominated by GHGs across all seasons. Over this time period, stratospheric ozone depletion exerts an influence comparable to GHGs but is restricted to austral spring and summer. Although anthropogenic aerosols show weaker effects on climate trends that oppose those induced by GHG forcing and ozone depletion, they have a noticeable impact. Notably, ozone recovery following the Montreal Protocol is currently weakening or reversing spring and summer trends in key circulation metrics. Finally, we quantify the degree to which the observed sea surface cooling of the Southern Ocean and Antarctic sea ice increase from 1980 to 2014 fall outside the models' ensemble spread. Our results highlight the need to better understand the roles of different forcings, model differences, and discrepancies between models and observations to constrain projections of future Southern Hemisphere climate change.

Journal of Geophysical Research AtmospheresVol. 131(16)
Israel Institute for Biological Research (IL), Pohang University of Science and Technology (KR), Bureau of Meteorology (AU), Met Office (GB), Statistics New Zealand (NZ), University of Leeds (GB), British Antarctic Survey (GB), Environment and Climate Change Canada (CA), Consejo Nacional de Investigaciones Científicas y Técnicas (AR), Hebrew University of Jerusalem (IL), Universidad de Buenos Aires (AR), GEOMAR Helmholtz Centre for Ocean Research Kiel (DE), University of Oxford (GB), University of Chicago (US), ARC Centre of Excellence in Future Low-Energy Electronics Technologies (AU), Education New Zealand (NZ), Ministry of Education (ME), CMCC Foundation - Euro-Mediterranean Center on Climate Change (IT), National Centre for Atmospheric Science (GB), NOAA Chemical Sciences Laboratory (US), Instituto Franco-Argentino sobre Estudios de Clima y sus Impactos (AR), University of Virginia (US), Fundación Ciencias Exactas y Naturales (AR), Monash University (AU), Colorado State University (US), Leipzig University (DE), UCLouvain (BE)
Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad de Buenos Aires, Natural Environment Research Council
Climate action
Openalex Percentile: Top 22%
Climate variability and models
DOIOpen Access PDFOpenAlex
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