Bolot et al. (2025) No decrease of tropical convection in individual deep convective systems with global warming

Identification

• Journal: npj Climate and Atmospheric Science
• Year: 2025
• Date: 2025-12-12
• Authors: Maximilien Bolot, Rémy Roca, Thomas Fiolleau, Caroline Muller
• DOI: 10.1038/s41612-025-01285-5

Research Groups

• LMD/IPSL, CNRS, ENS-PSL, Ecole Polytechnique, Sorbonne Université, Paris, France
• LEGOS/OMP, CNES, CNRS, IRD, Université Toulouse III, Toulouse, France
• Institute of Science and Technology Austria (ISTA), Klosterneuburg, Austria

Short Summary

This study challenges the consensus that tropical convection decreases with global warming by showing that individual deep convective systems intensify, with the overall decrease in tropical convection attributed to a reduction in the total number of such systems.

Objective

• To demonstrate that while aggregated tropical convective mass flux decreases with global warming, the mass flux within individual deep convective systems (DCSs) does not decrease and may even increase.

Study Configuration

• Spatial Scale: Long channel configuration (6144 km × 384 km) with 3 km horizontal resolution.
• Temporal Scale: 100-day simulations, with the last 25 days analyzed, for surface temperatures of 300 K and 305 K.

Methodology and Data

• Models used: System for Atmosphere Modeling (SAM) version 6.11.2 (cloud-resolving model), Rapid Radiative Transfer Model (RRTM), Tracking Of Organized Convection Algorithm through a 3-D segmentatioN (TOOCAN), RTTOV-13 (for OLR to brightness temperature conversion).
• Data sources: Kilometer-scale radiative-convective equilibrium (RCE) simulations from SAM, with model output converted to brightness temperature fields.

Main Results

• The aggregated convective mass flux and cloud coverage decrease with surface warming (e.g., approximately a 20% decrease in mass flux at the 250 K level between 300 K and 305 K simulations).
• The total number of Deep Convective Systems (DCSs) decreases significantly with warming (e.g., a 50% decrease from 4535 to 2323 DCSs between 300 K and 305 K simulations).
• The convective mass flux per individual DCS increases dramatically with warming across all durations, with longer-lived systems showing more pronounced increases (e.g., 6-8 hour lifetime DCSs double in mass flux, 12-14 hour lifetime DCSs nearly quadruple).
• The core surface area per individual DCS also increases with warming, mirroring the trend in individual mass flux.
• The convective mass flux density (mass flux per unit of core surface area) remains nearly invariant at approximately 0.32 kg m⁻² s⁻¹ between the 300 K and 305 K simulations, indicating that the increase in individual mass flux is primarily due to increased core surface area.
• Mechanical work performed in the convective cores increases by +12.7% K⁻¹.
• The invariance of mean pressure velocity in the core is robust to different core identification methods and across the distribution of DCS durations.

Contributions

• Challenges the prevailing scientific consensus by demonstrating that individual tropical deep convective systems intensify with global warming, rather than weakening.
• Provides a novel explanation for the observed decrease in total tropical convection, attributing it to a reduction in the number of convective systems rather than a decrease in the strength of individual systems.
• Highlights the remarkable and robust invariance of mean pressure velocity (or mass flux density) within convective cores, suggesting an important emerging property of convection under warming.
• Emphasizes the critical role of the physics of individual Deep Convective Systems (DCSs) in determining the overall tropical mass flux distribution.

Funding

• IPSL mesocenter ESPRI facility (supported by CNRS, UPMC, Labex L-IPSL, CNES, Ecole Polytechnique).
• CNES and CNRS support under the Megha-Tropiques program.
• European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Project CLUSTER, Grant Agreement No. 805041).

Citation

@article{Bolot2025No,
  author = {Bolot, Maximilien and Roca, Rémy and Fiolleau, Thomas and Muller, Caroline},
  title = {No decrease of tropical convection in individual deep convective systems with global warming},
  journal = {npj Climate and Atmospheric Science},
  year = {2025},
  doi = {10.1038/s41612-025-01285-5},
  url = {https://doi.org/10.1038/s41612-025-01285-5}
}