He, Jian, Li Zhang, Rebecca H Schwantes, Barry Baker, Larry W Horowitz, and Vaishali Naik, et al., March 2026: Incorporating gas-phase chemistry into the Unified Forecast System (UFS) for global air quality applications. Journal of Advances in Modeling Earth Systems, 18(3), DOI:10.1029/2025MS005299. Abstract
The Unified Forecast System (UFS) is a community-based Earth modeling system designed to support operational forecasts at the National Oceanic and Atmospheric Administration (NOAA), while also facilitating the integration of research advances from the broader scientific community. The Configurable ATmospheric Chemistry (CATChem) library and modeling component is being developed to include comprehensive chemical and aerosol processes for representing atmospheric composition through a flexible, easy-to-modify, and well-documented infrastructure. Here CATChem version 1.0 (v1.0) is linked to the UFS High Resolution 3 configuration to create the Unified Forecast System with Chemistry (UFS-Chem) v1.0. The configurability of UFS-Chem enables its use for both research and operational applications, reducing time and effort for transitions to operations and enhancing collaboration with the research community. As a first step toward this goal, the gas-phase chemistry from the Atmosphere Model version 4.1 (AM4.1), developed at NOAA Geophysical Fluid Dynamics Laboratory (GFDL), is incorporated into CATChem and linked to the UFS as the first UFS-Chem configuration for global air quality applications. The simulated atmospheric compositions are generally consistent with those in GFDL-AM4.1 and agree well with surface observations, aircraft measurements, and satellite retrievals (with biases mostly within 30%), demonstrating atmospheric chemistry is reasonably well represented in the model. This work documents model uncertainties and biases in UFS-Chem v1.0 to help prioritize further improvements in emissions and process-level representations. The new global configuration is shown to be robust in representing atmospheric composition and chemical processes and serves as a foundation for future development.
The continuous increase in atmospheric methane (CH4) concentrations over the past few decades has become a major concern due to its strong role as a greenhouse gas contributing to climate change. In this work, we investigate the changes in the global methane budget using a global chemistry-climate model constrained with methane and its isotopic observations. We apply spatially-resolved isotopic signatures to better constrain the methane sources and include methane-hydroxyl radical (OH) feedback to better represent methane sinks and lifetime in the model. While anthropogenic activities are found to be mainly responsible for the methane increase since the 1980s, the increasing OH trend simulated by the model plays a critical role in the global methane evolution. We find the observed post-2006 shift of δ13CH4 can be explained by increases in 13C-depleted agricultural and waste emissions in the tropics, coupled with decreasing 13C-enriched biomass burning emissions and an increasing OH trend. We also find post-2006 emission increases in energy and agriculture sectors are large enough to offset the increasing sinks (due to increasing OH), and therefore are shown to contribute to the post-2006 renewed methane growth. With CH4-OH feedback included in the model, the results show an increasing sensitivity to emission increases on methane concentrations and lifetime. Our study underscores the importance of OH in the global methane evolution. Neglecting changes in OH could potentially lead to misinterpreting emission changes with respect to the long-term observations of methane and δ13CH4.
Canadell, Josep G., Pedro M S Monteiro, Marcos H Costa, Leticia Cotrim da Cunha, Peter Cox, Alexey V Eliseev, Stephanie A Henson, Masao Ishii, Samuel Jaccard, Charles D Koven, Annalea Lohila, Prabir K Patra, Shilong Piao, Joeri Rogelj, Stephen Syampungani, Sönke Zaehle, Kirsten Zickfield, Jian He, and Vaishali Naik, et al., in press: Global Carbon and other Biogeochemical Cycles and Feedbacks. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, , Cambridge University Press. August 2021.
The hydroxyl radical (OH) is extremely reactive in the atmosphere and able to destroy many other chemicals, such as methane, a strong greenhouse gas that contributes significantly to global warming. Therefore, OH is very important for methane concentrations and lifetime. Changes in the meteorological features (e.g., temperature, wind patterns, and relative humidity) would affect OH in the atmosphere. In this study, we use a three-dimensional numerical model to understand the meteorological impacts on OH and the resulting impacts on methane budget and lifetime over 1980–2017. With different meteorological datasets, we find there is a 2% difference in global mean tropospheric OH concentrations, with much larger differences over tropics. We calculate methane sources and loss due to OH and find an 11.2 Tg yr−1 difference in the global mean methane sources with 8 Tg yr−1 difference in the tropics, and 0.24 years difference in methane lifetime between the two meteorological datasets.
Szopa, Sophie, Vaishali Naik, Bhupesh Adhikary, Paulo Artaxo, Terje Berntsen, William D Collins, Sandro Fuzzi, Laura Gallardo, Astrid Kiendler-Scharr, Zbigniew Klimont, Hong Liao, Nadine Unger, Prodromos Zanis, Paul Ginoux, Jian He, and Fabien Paulot, et al., August 2021: Short-Lived Climate Forcers In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge, United Kingdom and New York, NY, USA, Cambridge University Press, DOI:10.1017/9781009157896.008817-922.
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 CO2, 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 CO2 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.
Changes in atmospheric methane abundance have implications for both chemistry and climate as methane is both a strong greenhouse gas and an important precursor for tropospheric ozone. A better understanding of the drivers of trends and variability in methane abundance over the recent past is therefore critical for building confidence in projections of future methane levels. In this work, the representation of methane in the atmospheric chemistry model AM4.1 is improved by optimizing total methane emissions (to an annual mean of 576 ± 32 Tg yr−1) to match surface observations over 1980–2017. The simulations with optimized global emissions are in general able to capture the observed global trend, variability, seasonal cycle, and latitudinal gradient of methane. Simulations with different emission adjustments suggest that increases in methane sources (mainly from energy and waste sectors) balanced by increases in methane sinks (mainly due to increases in OH levels) lead to methane stabilization (with an imbalance of 5 Tg yr−1) during 1999–2006, and that increases in methane sources combined with little change in sinks (despite small decreases in OH levels) during 2007–2012 lead to renewed methane growth (with an imbalance of 14 Tg yr−1 for 2007–2017). Compared to 1999–2006, both methane emissions and sinks are greater (by 31 Tg yr−1 and 22 Tg yr−1, respectively) during 2007–2017. Our results also indicate that the energy sector is more likely a major contributor to the methane renewed growth after 2006 than wetland, as increases in wetland emissions alone are not able to explain the renewed methane growth with constant anthropogenic emissions. In addition, a significant increase in wetland emissions would be required starting in 2006, if anthropogenic emissions declined, for wetland emissions to drive renewed growth in methane, which is a less likely scenario. Simulations with varying OH levels indicate that 1 % change in OH levels could lead to an annual mean of ~ 4 Tg yr−1 difference in the optimized emissions and 0.08 year difference in the estimated tropospheric methane lifetime. Continued increases in methane emissions along with decreases in tropospheric OH concentrations during 2008–2015 prolong methane lifetime and therefore amplify the response of methane concentrations to emission changes. Uncertainties still exist in the partitioning of emissions among individual sources and regions.
We describe the baseline model configuration and simulation characteristics of the Geophysical Fluid Dynamics Laboratory (GFDL)'s Atmosphere Model version 4.1 (AM4.1), which builds on developments at GFDL over 2013–2018 for coupled carbon‐chemistry‐climate simulation as part of the sixth phase of the Coupled Model Intercomparison Project. In contrast with GFDL's AM4.0 development effort, which focused on physical and aerosol interactions and which is used as the atmospheric component of CM4.0, AM4.1 focuses on comprehensiveness of Earth system interactions. Key features of this model include doubled horizontal resolution of the atmosphere (~200 to ~100 km) with revised dynamics and physics from GFDL's previous‐generation AM3 atmospheric chemistry‐climate model. AM4.1 features improved representation of atmospheric chemical composition, including aerosol and aerosol precursor emissions, key land‐atmosphere interactions, comprehensive land‐atmosphere‐ocean cycling of dust and iron, and interactive ocean‐atmosphere cycling of reactive nitrogen. AM4.1 provides vast improvements in fidelity over AM3, captures most of AM4.0's baseline simulations characteristics, and notably improves on AM4.0 in the representation of aerosols over the Southern Ocean, India, and China—even with its interactive chemistry representation—and in its manifestation of sudden stratospheric warmings in the coldest months. Distributions of reactive nitrogen and sulfur species, carbon monoxide, and ozone are all substantially improved over AM3. Fidelity concerns include degradation of upper atmosphere equatorial winds and of aerosols in some regions.
