Singer et al. (2025) Southern Ocean Clear‐Sky Brightening From Sea Spray Aerosol Increase Drives Departure From Hemispheric Albedo Symmetry

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Geophysical Research Letters
• Year: 2025
• Date: 2025-12-26
• Authors: Clare E. Singer, Robert Pincus
• DOI: 10.1029/2025gl119637

Research Groups

Not available from the abstract.

Short Summary

This study investigates negative trends in reflected shortwave radiation over the 21st century, finding global darkening driven by clouds, while clear-sky signals show offsetting hemispheric trends. It reveals an unexpected widespread clear-sky brightening over the Southern Hemisphere, particularly the Southern Ocean, which is attributed to increased wind-driven sea spray aerosol emissions linked to rising near-surface winds.

Objective

• To investigate the drivers of observed negative trends in reflected shortwave radiation over the 21st century, focusing on global, hemispheric, and clear-sky versus cloudy-sky contributions, and to understand the mechanisms behind observed regional anomalies.

Study Configuration

• Spatial Scale: Global, hemispheric (Northern Hemisphere, Southern Hemisphere), with a specific focus on the remote Southern Ocean.
• Temporal Scale: Over the 21st century (long-term trends).

Methodology and Data

• Models used: None explicitly stated as used for simulations/predictions; the analysis is observation-based.
• Data sources: Observations of reflected shortwave radiation, aerosol optical depth (AOD), and monthly-mean near-surface wind speed.

Main Results

• Significant negative trends in reflected shortwave radiation have been observed globally over the 21st century.
• Global-mean darkening is primarily driven by clouds.
• The global-mean atmospheric clear-sky signal is near zero due to offsetting trends between the two hemispheres.
• Northern Hemisphere clear-sky darkening is dominated by reduced anthropogenic aerosol emissions over population centers.
• The Southern Hemisphere (SH) exhibits an unexpected widespread atmospheric clear-sky brightening, particularly over the remote Southern Ocean (SO).
• This SO brightening is ascribed to an increase in aerosol optical depth (AOD).
• Trends in SO AOD are concluded to originate from enhanced wind-driven sea spray aerosol emissions, which are driven by increasing near-surface winds.

Contributions

• Identifies and quantifies the unexpected widespread atmospheric clear-sky brightening over the Southern Hemisphere, especially the remote Southern Ocean.
• Provides a novel explanation for this brightening, linking it to increased wind-driven sea spray aerosol emissions caused by rising near-surface winds.
• Discusses the implications of Southern Ocean brightening for deviations from observed hemispheric albedo symmetry and its potential role as a negative Earth system feedback.

Funding

Not available from the abstract.

Citation

@article{Singer2025Southern,
  author = {Singer, Clare E. and Pincus, Robert},
  title = {Southern Ocean Clear‐Sky Brightening From Sea Spray Aerosol Increase Drives Departure From Hemispheric Albedo Symmetry},
  journal = {Geophysical Research Letters},
  year = {2025},
  doi = {10.1029/2025gl119637},
  url = {https://doi.org/10.1029/2025gl119637}
}