NOAA GFDL - Geophysical Fluid Dynamics LaboratoryGFDL - Geophysical Fluid Dynamics Laboratory

Quantifying Equilibrium Climate Sensitivity to Atmospheric Chemistry and Composition Representations in GFDL-CM4.0 and GFDL-ESM4.1

April 14th, 2026

Key Findings

  • Equilibrium climate sensitivity (ECS) is 0.7 K (21%) lower in the Earth system model GFDL-ESM4.1 than in the corresponding physical climate model GFDL-CM4.0, which does not include interactive aerosols and chemistry.
  • Five climate–chemistry feedbacks (dust, sea salt, organic aerosols, ozone, and marine aerosols) each reduce ECS by 0.1–0.3 K and contribute 0.4–0.6 K combined to the total reduction, with broadly uniform global effects.
  • Interactive stratospheric ozone produces the largest single reduction in ECS and moderates polar amplification of warming.
  • Climate sensitivity depends in part on how atmospheric chemistry and composition are represented in models.

Lori T. Sentman, John P. Dunne, Larry W. Horowitz, Vaishali Naik, Fabien Paulot, Paul Ginoux, and Niki Zadeh. Geophysical Research Letters DOI: 10.1029/2025GL116545

Equilibrium climate sensitivity (ECS) measures the long-term global surface temperature response to a doubling of preindustrial carbon dioxide. While greenhouse gases are the primary driver of warming, atmospheric aerosols and chemical processes also influence how the climate system responds. In this study, GFDL scientists used simplified but closely related configurations of two GFDL models to isolate the role of atmospheric chemistry and composition. The physical climate model, GFDL-CM4.0, does not include interactive aerosols and chemistry. The Earth system model, GFDL-ESM4.1, includes interactive dust, sea salt, organic aerosols, ozone, and marine aerosols, along with carbon–climate interactions.

The results show that including these interactive chemistry and aerosol processes reduces ECS by 0.7 K relative to the physical model. Each feedback contributes modest cooling individually, but together they account for most of the difference in global temperature response. The combined effect is geographically widespread. Interactive stratospheric ozone has the largest influence and reduces the magnitude of polar amplification. These findings demonstrate that projected global warming is sensitive to how atmospheric composition is represented in climate models. Although individual feedbacks may appear small in isolation, their cumulative impact can meaningfully alter estimates of long-term warming. The study provides quantitative guidance for improving model representation of atmospheric chemistry and strengthens confidence in projections that inform climate assessment and decision-making.

Individual and Combined Climate–Chemistry Feedback Effects on ECS Relative to CM4
Graph of Individual and Combined Climate–Chemistry Feedback Effects on ECS Relative to CM4
Change in equilibrium climate sensitivity (ΔECS, K) relative to GFDL-CM4.0 resulting from the addition of five climate–carbon–chemistry representations included in GFDL-ESM4.1. Individual contributions are shown for (1) interactive stratospheric ozone (O3, orange), (2) interactive biogenic volatile organic compound emissions (BVOC, green), (3) temperature-dependent sea salt emissions (SEASALT, purple), (4) climate-responsive dust emissions (DUST, brown), and (5) a sea ice mask that limits marine aerosol exchange over sea ice (NOICEMASK, magenta). The summed contribution of the individual drivers (SUM, multicolor) is compared with the fully interactive simulation including all five processes simultaneously (COMBINED, blue), along with the ECS of the full ESM4 configuration (ESM4, black). Error bars indicate one standard deviation in ΔECS. Results show that interactive atmospheric chemistry and aerosol processes collectively reduce ECS relative to CM4, with broadly distributed global effects and notable influence from stratospheric ozone.