The GFDL Earth System Model Version 4.1 (GFDL‐ESM 4.1): Overall Coupled Model Description and Simulation Characteristics

TLDR

The GFDL Earth System Model Version 4.1 (ESM4.1) is a baseline coupled model developed from 2013–2018 to support CMIP6 carbon‑chemistry‑climate simulations, emphasizing comprehensive Earth‑system interactions rather than solely ocean resolution as in CM4.0. ESM4.1 doubles the horizontal resolution of the atmosphere (2°→1°) and ocean (1°→0.5°) and integrates advances in dynamics, physics, aerosols, land‑ecosystem, fire, ocean biogeochemistry, and coupled CO₂, dust, iron, and nitrogen cycles. ESM4.1 delivers higher fidelity in CO₂ and chemistry, improves Southern Ocean dynamics and aerosol representation, and reduces spurious ocean heat uptake, while lowering transient and equilibrium climate sensitivity, though it shows moderate sea‑surface temperature bias degradation, regional aerosol degradation, and strong centennial‑scale climate modulation by Southern Ocean convection.

Abstract

Abstract We describe the baseline coupled model configuration and simulation characteristics of GFDL's Earth System Model Version 4.1 (ESM4.1), which builds on component and coupled model developments at GFDL over 2013–2018 for coupled carbon‐chemistry‐climate simulation contributing to the sixth phase of the Coupled Model Intercomparison Project. In contrast with GFDL's CM4.0 development effort that focuses on ocean resolution for physical climate, ESM4.1 focuses on comprehensiveness of Earth system interactions. ESM4.1 features doubled horizontal resolution of both atmosphere (2° to 1°) and ocean (1° to 0.5°) relative to GFDL's previous‐generation coupled ESM2‐carbon and CM3‐chemistry models. ESM4.1 brings together key representational advances in CM4.0 dynamics and physics along with those in aerosols and their precursor emissions, land ecosystem vegetation and canopy competition, and multiday fire; ocean ecological and biogeochemical interactions, comprehensive land‐atmosphere‐ocean cycling of CO 2 , dust and iron, and interactive ocean‐atmosphere nitrogen cycling are described in detail across this volume of JAMES and presented here in terms of the overall coupling and resulting fidelity. ESM4.1 provides much improved fidelity in CO 2 and chemistry over ESM2 and CM3, captures most of CM4.0's baseline simulations characteristics, and notably improves on CM4.0 in (1) Southern Ocean mode and intermediate water ventilation, (2) Southern Ocean aerosols, and (3) reduced spurious ocean heat uptake. ESM4.1 has reduced transient and equilibrium climate sensitivity compared to CM4.0. Fidelity concerns include (1) moderate degradation in sea surface temperature biases, (2) degradation in aerosols in some regions, and (3) strong centennial scale climate modulation by Southern Ocean convection.