February 2026 Newsletter Issue
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In this Newsletter:
Chief Scientist Message
Is the High ECS in CESM2 Degrading Transient Climate Change Projections Over the 21st Century?
New computer simulations reveal the Earth system in unprecedented detail
Help Shape the Next Generation of Isotope-Enabled CESM (iCESM3): User Survey
CESM Winter Working Group Meetings
2026 CESM Workshop
2026 CESM Tutorial
Research Highlights from Our Community
Quick Links
Chief Scientist Message
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Dear CESM colleagues,
As we push towards the finalization and release of CESM3 later this year, we look forward to your continued engagement, interest, and contributions to the CESM project. Below are reminders of some community CESM activities in 2026.
- The CESM Winter Working Group meetings are taking place over the month of February and into early March, see below for more details. Registration for remote participation will remain open throughout the meetings.
- The CESM Annual Workshop is scheduled for June 15-17, 2026 at the Center Green campus in Boulder. Requests for nominations for Outstanding Accomplishment and Graduate Student awards will go out in early February.
- The CESM tutorial will be July 6-10, 2026. Applications are being accepted through February 17, 2026.
And, as always, there will be many additional CESM-relevant activities. For example, we are collaborating with the ICON machine learning (ML) team to build hybrid (ML plus physics) versions of CESM and ICON. In support of this activity, we are hosting a Hybrid Model Implementation Workshop, June 8-12. And, there will be a S2S Land-Atmosphere Interactions Workshop on Aug 4-6. And, the LMWG and BGCWGs are starting to plan for a CLM tutorial in the fall. I hope to see many of you at one or more of these events.
In this Newsletter, we highlight several new Research Highlights from our CESM community. But, before getting to those, I want to draw your attention to the following paper, led by Margaret Duffy now at UC Davis, that evaluates how the high Equilibrium Climate Sensitivity in CESM2 affects transient climate change projections and provides guidance about situations where researchers should exercise more caution when using or analyzing CESM2. Also in this Newsletter, we announce the release of the MESACLIP high resolution CESM1 simulations and we solicit your input on priorities for the isotope-enabled version of CESM3 that we have started to develop through the recently funded NSF SCI-SWIM project.
Best,
Dave
Is the High ECS in CESM2 Degrading Transient Climate Change Projections Over the 21st Century?
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Figure 1: (a) Time series of 5-year running-mean global-mean Ts anomalies over 1850–2100 for the Berkeley Earth Surface Temperature (Rohde & Hausfather, 2020) observation-based data set (black), Community Earth System Model version 2 (CESM2) at 2° (blue), paleocalibr CESM2 (green), the minimum to maximum range of the LENS2 which uses CESM2 1° (salmon), and other CMIP6 models (gray). Anomalies are relative to the 1850 to 1900 average. Historical forcing is used from 1850 to 2015 and SSP3–7.0 is used thereafter. (b) equilibrium climate sensitivity (ECS) versus transient climate response for the 34 CMIP6 models from Table 2 of Meehl et al. (2020) along with CESM2 1° (salmon), CESM2 2° (blue), paleocalibr CESM2 (green), and CESM1 1° using values from Bacmeister et al. (2020) (purple). ECS values are calculated using the Gregory regression method. (c) Time series of 5-year running-mean global-mean ΔTs in 1pctCO2 experiments for CESM2 2° (blue), paleocalibr CESM2 (green), CESM2 1° (salmon), and other CMIP6 models (gray). Anomalies relative to the preindustrial control. Panel (d) as in (c) but with abrupt4xCO2 experiments. |
Margaret L. Duffy, Isla R. Simpson, Brian Medeiros, Jiang Zhu, Christina S. McCluskey, Adam R. Herrington, Andrew Gettelman, Bette L. Otto-Bliesner, John T. Fasullo, Peter H. Lauritzen, Richard B. Neale, David M. Lawrence
CESM2 has a higher equilibrium climate sensitivity (ECS) than many CMIP6 models, than the previous generation of CESM, and than estimates from other lines of evidence. Since its release, global-mean surface temperature changes in CESM2 have been evaluated against paleoclimate evidence which revealed that it simulates a too-cold Last Glacial Maximum (LGM) unless a set of modifications that we refer to as “PaleoCalibr” is used. Included in that configuration is a modification to an inappropriate upper limit on cloud ice number concentration. In addition to better agreement with the LGM, these PaleoCalibr modifications lowered the ECS. In light of these findings, we provide guidance for users of CESM2. We find that the PaleoCalibr modifications do not alter the transient climate response and that the PaleoCalibr modifications do not alter the 20th or 21st century climates under SSP3–7.0 warming scenario. Therefore, the impacts of high ECS and the inappropriate upper limit on cloud ice number concentration do not appear to be significant under moderate warming. It is only under more extreme climate changes where CESM2 and the PaleoCalibr CESM2 diverge.
New computer simulations reveal the Earth system in unprecedented detail
Caption
The high-resolution simulations in the MESACLIP dataset include such features as snow cover on land and sea surface temperatures in the oceans. |
Leveraging the power of two of the nation’s leading supercomputers, a team of scientists at Texas A&M University and NSF NCAR has created an unprecedented set of high-resolution Earth system simulations. The dataset is now freely available to the scientific community, offering a remarkable opportunity to gain new insights into climate variability and how future changes may affect specific regions.
The project, called MESACLIP and funded by the NSF, is unique with an ensemble of high-resolution runs that sample the inherent, natural fluctuations of the Earth’s climate system. The massive dataset, weighing in at over six petabytes, provides scientists with an extraordinary trove of simulations spanning more than 4,500 years of past, present, and future climate on which to conduct research. (Excerpted from NCAR News Article by David Hosansky).
This recently published article highlights one of the many scientific applications of this unique dataset.
Title: Future extreme precipitation amplified by intensified mesoscale moisture convergence
Authors: Ping Chang, Dan Fu, Xue Liu, Frederic S. Castruccio, Andreas F. Prein, Gokhan Danabasoglu, Xiaoqi Wang, Julio Bacmeister, Qiuying Zhang, Nan Rosenbloom, Teagan King, and Susan C. Bates
Journal: Nature Geoscience
Help Shape the Next Generation of Isotope-Enabled CESM (iCESM3): User Survey
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As previously announced, water-isotope and water-tracking capabilities are returning to the Community Earth System Model (CESM) through the SCI-SWIM project (Sustainable Community Infrastructure for Stable Water Isotope Modeling Enabling Earth System Research), supported by the NSF Cyberinfrastructure for Sustained Scientific Innovation (CSSI) program. SCI-SWIM is developing a modern, next-generation isotope-enabled CESM version 3 (iCESM3) that will provide the community with robust, maintainable tools for stable water isotope modeling across the Earth system.
To ensure that iCESM3 meets the needs of both current and future users, we invite you to complete the iCESM User Survey. Your input will directly inform model development priorities, documentation, and user support as we build a sustainable infrastructure for isotope-enabled CESM.
CESM Winter Working Group Meetings
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2025 CESM Atmosphere Model Winter Working Group |
The 2026 CESM Winter Working Group Meetings are happening! The Working Groups include a full slate of gatherings bringing together the CESM community to share research, collaborate across disciplines, and shape the future of Earth system modeling. Meetings will take place throughout February and early March, with both in-person and virtual participation options available. Note also that links to the presentations will be available soon after the workshops end.
February 2nd-4th, 2026: Atmosphere, Chemistry, and Whole Atmosphere Working Groups
The winter meetings kicked off at the Mesa Lab on Monday, February 2nd through Wednesday, February 4th. These meetings included the Atmosphere Model Working Group (AMWG), Chemistry–Aerosol Working group (CAWG) (formerly the Chemistry Climate Working Group), Earth System Prediction Working Group (ESPWG), Climate Variability and Change Working Group (CVCWG), and the Whole Atmosphere Working Group (WAWG).
Presentations from these Working Groups can be found online.
February 5th–6th, 2026: Polar Climate and Ocean Model Working Groups
The Polar Climate Working Group (PCWG) and Ocean Model Working Group (OMWG) meetings will be held on Thursday, February 5th, and Friday, February 6th.
The OMWG supports CESM’s broad scientific objectives by developing and maintaining a state-of-the-science ocean component model. The group is currently transitioning from POP2 to MOM6, a shift that will increase flexibility, usability, and accuracy while enabling new research directions, including coupling with dynamic ice sheets and regional and coastal models.
The PCWG brings together scientists focused on understanding Arctic and Antarctic climate processes and their influence on the global climate system. The group also develops and maintains the CESM sea ice model, CICE, and welcomes contributions spanning the ocean, ice, and atmosphere.
Agendas for both meetings are available on the CESM website. Registration for remote participation will remain open through the meeting.
February 11th–12th, 2026: Land Ice and Paleoclimate Working Groups
The Land Ice Working Group (LIWG) meeting takes place on Wednesday, February 11th. This one-day meeting welcomes anyone interested in land ice science and includes both oral presentations and discussion sessions. Topics range from early-stage conceptual ideas to recently published research. Registration to join online remains open through the meeting.
The Paleoclimate Working Group meets on Thursday, February 12th. Researchers are invited to register and present work on paleoclimate modeling, proxy data development, and model–data synthesis. Registration to join online remains open throughout the meetings.
February 24th–26th, 2026: Land Model and Biogeochemistry Working Group
The Land Model and Biogeochemistry (BGC) Working Group meeting will be held Tuesday, February 24th through Thursday, February 26th.
The deadline to submit a talk is February 6th, 2026.
The deadline to register for in-person attendance is February 18th, 2026.
March 5th-6th, 2026: Software Engineering Working Group
The CESM Software Engineering Working Group will host its winter meeting on March 5th–6th, featuring a hackathon focused on infrastructure development with close collaborators. The meeting will also include two talk sessions: one on code (led by Brian Dobbins) and another on refactoring Fortran code for improved GPU performance, followed by a discussion on best practices and challenges.
Deadline to submit a hackathon project or GPU-related abstract: February 18th, 2026
Deadline to register for in-person attendance: February 27th, 2026
Participants are welcome to attend either in person or online.
For full details, agendas, and registration information, visit the CESM Winter Working Group Meetings website.
If you have questions, please contact Elizabeth Faircloth. We look forward to your participation in the 2026 CESM Winter Working Group Meetings!
2026 CESM Workshop
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Group Photo from the 2025 CESM Workshop |
There are less than 4 months until the 2026 CESM Workshop! This flagship CESM community event brings together scientists, developers, and users from around the world to share the latest advances in Earth system modeling, highlight new CESM developments, and foster collaboration across disciplines.
The CESM Workshop provides a forum for presentations, discussions, and community engagement focused on model development, scientific applications, and emerging challenges and opportunities in Earth system science. Attendees can expect a dynamic program featuring invited talks, contributed presentations, and opportunities to connect with the broader CESM community.
The 2026 CESM Workshop will take place June 15–17, 2026 in Boulder, CO.
Be sure to mark your calendar and check back on the CESM website for upcoming details, including registration information, abstract submission deadlines, and the full agenda. We look forward to seeing you in Boulder this June!
2026 CESM Tutorial
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CESM Tutorial Participants 2025 |
The 2026 CESM Tutorial will take place July 6–10th, 2026, and applications are now open.
This in-depth, hands-on tutorial is designed for participants with little to no prior experience using CESM. The goal is to provide attendees with a strong scientific foundation in CESM components and the essential skills needed to begin running and modifying the model with confidence.
Participants will engage in:
- Guided sessions on running CESM, modifying model components, and analyzing model output
- Small-group discussions with CESM scientists
- Dedicated time for student and early-career networking
Who Should Apply:
- We welcome applications from graduate students, postdoctoral researchers, research scientists, and faculty members, particularly those whose research or career goals would benefit from using CESM.
Format:
- The 2026 CESM Tutorial will be held in person. Additional details about the agenda and daily schedule will be posted to the CESM website as they become available.
Cost & Support:
- There is no cost to apply or attend the tutorial. Limited travel support may be available for selected participants.
Application Deadline:
- Tuesday, February 17, 2026 at 11:59 PM (Mountain Time)
- Applicants will be notified of decisions by April 24, 2026
If you’re looking to build a strong foundation in CESM and connect with the broader modeling community, we encourage you to apply soon!
Research Highlights from Our Community
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Fig. 1: Comparison of observed and simulated extreme DSLs from 1920 to 2020 from "Storm-permitting climate modeling highlights storm frequency’s role in future extreme sea level changes along US East and Gulf coasts" |
Modeled Global Impacts of Chlorine Oxidation and Temperature Dependence on the Atmospheric Lifetime and Concentrations of Volatile Methyl Siloxanes
Christopher E Brunet, Saeideh Mohammadi, Behrooz Roozitalab, Nora K Gibson, Rafael P Fernandez, Alfonso Saiz-Lopez, Keri C Hornbuckle, Charles O Stanier
Volatile methyl siloxanes (VMS) are high production volume chemicals found in a wide range of consumer items such as personal care products. VMS have attracted scrutiny due to long-range environmental transport (LRET) concerns. However, their emissions, lifetimes, and concentrations remain uncertain, in part because of limitations in previous atmospheric modeling. Herein, we describe the global modeling of siloxanes: D4 (octamethylcyclotetrasiloxane), D5 (decamethylcyclopentasiloxane), and D6 (dodecamethylcyclohexasiloxane) in the Community Earth System Model (CESM2-SLH) using an updated chemical mechanism that includes chlorine radical oxidation and temperature-dependent reaction rates. With these previously unconsidered factors, we predicted VMS lifetimes ranging between 2.7 and 6.7 days and annual average D5 near-surface concentrations as high as 4.5 ng m-3 in the remote Arctic and 160 ng m-3 in urban areas. These lifetimes and the degree of LRET were significantly lower than previously reported. OH remained the largest loss pathway, although it decreased at low temperatures relative to previous modeling. The temperature-induced lifetime increase was outweighed by the previously unconsidered chlorine oxidation channel. Model results and previous measurements agreed relatively well but exhibited negative normalized biases (-0.55 to -0.88), particularly in urban areas not well-resolved at global model resolution, and for passive sampler measurements.
A new NMVOCs emission inventory for China: Impact on O3 and PM2.5 regional simulations and assessment of recent industrial NMVOCs emission abatement policies
Wendong Ge, Di Wang, Yang Ren, Yuhan Zhou, Xinyang Liu, Dongting Wei, Junfeng Liu
With the increasing ozone (O3) pollution and slowing down trend of fine particulate matter (PM2.5) reduction in China in recent years, volatile organic compounds (VOCs) as common precursors are playing a more important role, with stronger demand to clarify their emissions, verify their simulations and evaluate their regional influences. This study aims to introduce a comprehensive anthropogenic non-methane VOCs (NMVOCs) emission inventory in China in 2019, comprehensively assess the impact on NMVOCs, O3 and PM2.5 simulations, and investigate the effect of recent VOCs-related industrial policies and technologies at a regional scale using the Community Earth System Model version 2 (CESM2). The results show that Jiangsu, Shandong, Zhejiang and Guangdong provinces account for the largest anthropogenic emissions (44 % collectively), and solvent utilization and industrial processes are two dominated sectors of NMVOCs emission sources (>70 % collectively). The hydrocarbon simulations are closer to observations with updated emission inventories. The implementation of NMVOCs emission reduction technologies can effectively reduce most components of NMVOCs in China by over 12 %, and is beneficial to the coordinated control of PM2.5 (9 % reduction nationally) and O3 pollutions (2 % reduction nationally) in most regions of China as well as co-benefits for neighboring countries and regions (1 %∼10 % pollutant reductions). This study suggested that the future VOCs control in China needs to focus more on aromatics and alkenes in the Yangtze River Delta and parts of the North China Plain.
Plant functional trait uncertainty can outweigh climate scenario uncertainty in tundra ecosystem productivity
Katya R. Jay, William R. Wieder, Sarah C. Elmendorf, Marko J. Spasojevic, Katharine N. Suding
- Predicting shifts in species composition with global change remains challenging, but plant functional traits provide a key link to scale from plant to community and ecosystem levels. The extent to which functional trait shifts may mediate ecosystem response to climate change remains a critical question.
- We ran point-scale Community Land Model (CLM) simulations with site-specific functional trait and phenology observations to represent alpine tundra growth strategies. We validated our results with site observations and compared parameterized results to those using the default parameterization. We then quantified the relative contribution of plant functional trait shifts vs climate change scenarios (and the resulting phenological shifts) to uncertainty in future tundra ecosystem productivity outcomes.
- We found that using community-specific functional traits and phenology observations significantly improved productivity estimates compared with overestimates in a default simulation. Uncertainty in potential plant trait shifts often had a larger effect on ecosystem productivity responses than uncertainty in the forced response from different climate change scenarios.
- These findings highlight the key role of functional traits in shaping vegetation responses to climate change and the value of incorporating site-level measurements into land models to more accurately forecast climate change impacts on ecosystem function.
Biophysical impacts of urbanization on climate change and vegetation in Borneo Island
Danbi Lee, Ji-Hoon Oh, Jonghun Kam, So-Won Park, Jong-Seong Kug
Urbanization causes compounding adverse impacts with climate change on regional ecology and society through biophysical processes. Borneo Island in Indonesia has been undergoing rapid urbanization, but the compounding impacts of urbanization under climate change remain unknown. Here, we investigate how idealized urbanization affects regional climate and vegetation using Community Earth System Model version 2 (CESM2) simulations with two land cover scenarios for Borneo: an urbanization scenario and a control scenario with no urbanization for the 2025–2034 period. Results show that urbanization in Borneo alters surface biophysical properties, imbalances the regional surface water budget, and thus leads to a warmer (+0.25 °C) and drier (−0.17 mm/day) climate across the island, with particularly pronounced effects on the dry period climate. Furthermore, these urbanization-induced climate responses contribute to additional vegetation loss. Moreover, vegetation in Kalimantan, the site of Indonesia's new capital, is also sensitive to the combined impacts of urbanization and climate change. This study highlights the importance of considering biophysical climate effects when assessing the compounding impacts of urbanization. This approach can help guide policymakers in updating current climate adaptation plans for sustainable urban development.
Storm-permitting climate modeling highlights storm frequency’s role in future extreme sea level changes along US East and Gulf coasts
Gaopeng Xu, Ping Chang, Gokhan Danabasoglu, Frederic S. Castruccio, Stephen Yeager, Qiuying Zhang, Jaison Kurian, Justin Small, Susan Bates & Christine C. Shepard
Storm-induced coastal extreme sea levels (ESLs) pose severe threats to infrastructure, economies, and ecosystems. However, projecting future ESL changes is hindered by the coarse resolution of climate models used in assessment reports, which fail to accurately capture tropical cyclones (TCs) and nor’easters. Here, we demonstrate that high-resolution Community Earth System Model (CESM) simulations realistically reproduce observed wind- and pressure-induced daily-mean extreme dynamic sea levels (DSLs), including the most extreme events. Under a high-emission scenario, we show that 50-year return DSLs (DSL50) decrease along the U.S. Texas and Northeast coasts but increase along the U.S., Louisiana, and Southeast coasts from 2006 to 2100, creating substantial spatial discrepancies between total DSL50 changes and mean DSL rise. Along the Gulf and Southeast coasts, DSL50 trends are primarily driven by TC frequency changes, while nor’easter frequency changes tend to govern trends along the Northeast coast. These findings challenge the traditional assumption of stationarity in storm-induced ESLs, underscore the importance of high-resolution climate models for regional coastal risk assessment, and represent a critical step toward more accurate projections of future ESLs in a warming climate.
Increased Continental Exposure as a Driver of Carbon Drawdown and Initiation of the Late Paleozoic Ice Age
Yinggang Zhang, Shuai Yuan, Benjamin J. W. Mills, Andrew S. Merdith, Yongyun Hu, Maoyan Zhu
During the middle to late Devonian period, Earth gradually cooled, eventually entering the Late Paleozoic Ice Age—the longest icehouse interval in Earth's history. This cooling is widely thought to have been driven by the removal of carbon dioxide (CO2) from the atmosphere through rock weathering, but earlier models could not reproduce the timing of glaciation. In this study, we combined a high-resolution climate model with a biogeochemical model to represent the weathering process at higher resolution in space and time. Our results show that the exposure of more continental land area, caused by long-term sea level fall as the supercontinent Pangea assembled, enhanced weathering fluxes and removed CO2 from the atmosphere, as well as making the Earth's surface more reflective. This mechanism helps explain why the Late Paleozoic Ice Age began when it did. The findings highlight the role of continental exposure in shaping Earth's long-term climate and demonstrate the importance of high-resolution climate models in understanding both past and future climate changes.
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Thanks for reading this CESM Newsletter! Expect to see the next one in the Summer of 2026. Please send potential Newsletter items to Elizabeth Faircloth.
