Hemispherically asymmetric Hadley cell response to CO₂ removal

Area of Science:

• Earth System Science
• Climate Dynamics
• Atmospheric Science

Background:

• The Hadley cell (HC) edge shifts poleward with climate warming, expanding dry subtropical regions.
• Previous studies have documented this poleward HC shift but its reversibility remains unclear.

Purpose of the Study:

• To investigate whether the poleward shift of the Hadley cell edge is reversible upon carbon dioxide (CO2) removal.
• To understand the implications of CO2 removal on subtropical climate and dryness.

Main Methods:

• Conducted large-ensemble climate model experiments.
• Systematically increased CO2 concentrations, followed by a decrease to present-day levels.
• Analyzed changes in Hadley cell edge position and vertical wind shear.

Main Results:

• The poleward-shifted Hadley cell edge does not return to its pre-warming position after CO2 reduction.
• Observed a persistent poleward shift in the Southern Hemisphere HC edge.
• Observed an equatorward shift in the Northern Hemisphere HC edge, resulting in hemispheric asymmetry.
• Asymmetric HC changes are linked to ocean response adjustment times and altered vertical wind shear.

Conclusions:

• CO2 removal does not guarantee the full recovery of Hadley cell dynamics altered by warming.
• Persistent hemispheric asymmetries in HC edge position suggest long-term climate impacts.
• Subtropical dryness associated with HC changes may not be fully reversible through CO2 reduction alone.