Welcome to the Community Earth System Model (CESM) Newsletter. Want to receive our next newsletter in your inbox? Visit our newsletter page to subscribe and never miss a newsletter.

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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

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Chief Scientist Message

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

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Is the High ECS in CESM2 Degrading Transient Climate Change Projections Over the 21st Century?

Caption 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.

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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

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Help Shape the Next Generation of Isotope-Enabled CESM (iCESM3): User Survey

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.

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CESM Winter Working Group Meetings

Caption 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.

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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. 

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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. 

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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.

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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.

Register online.

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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.

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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!

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2026 CESM Workshop

Caption 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!

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2026 CESM Tutorial 

Caption 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!

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Research Highlights from Our Community

Caption 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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Simpler Models Information

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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.

Welcome to the Community Earth System Model (CESM) Newsletter. Want to receive our next newsletter in your inbox? Visit our newsletter page to subscribe and never miss a newsletter.

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In this Newsletter:

Chief Scientist Message

2026 CESM Workshop

New CESM Working Group Co-Chairs

2026 Crocodile Workshop

From Earth System Science to Sustainability: A TNC-NCAR Collaboration

Research Highlights from Our Community

Quick Links

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Chief Scientist Message

Looking back on my message for the spring CESM Newsletter from last year, I have a sense of déjà vu. In that newsletter, I acknowledged the anxiety and sadness driven by the external pressures on science. And, I noted that despite this, we were continuing to work to produce a final configuration for CESM3. Well, the anxiety and sadness is ongoing, and we are still working on CESM3! As anticipated from past experience, we encountered and overcame many challenges as we finalized CESM3. But, we are now ‘done’ and are in the lengthy process of spinning the coupled model up. The 31st Annual CESM Workshop this summer will be an opportunity for us to share progress and (hopefully!) announce a CESM3 release date.  

We are making good progress on other CESM initiatives as well, including the machine learning enhanced version of CESM (CESM3-MLe), a high resolution version, km-scale capabilities, interoperability with MPAS, the reintroduction of water isotopes and water tracking, regional versions of MOM6, along with lots of interesting and innovative new science. As always, we look forward to seeing our colleagues at the annual CESM Workshop, where we can catch up on all the great CESM-related science and development and form new projects and collaborations. 

Summer is always a busy time at NCAR with lots of visitors, workshops, and the tutorial.  Here are a few upcoming events:

• Hybrid Model Implementation Workshop, June 8-12
• CESM Tutorial, July 6-10
• S2S Land-Atmosphere Interactions Workshop, Aug 4-6
• Broadening Earth System Research Across Scales with High-Resolution Modeling Workshop, Sept 14-17
• Regional Ocean Modeling with MOM6 in the Community Earth System Model Framework, Sept 28-Oct 2

I’m looking forward to catching up with colleagues at one or more of these events.

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2026 CESM Workshop

The 2026 CESM Workshop is right around the corner! We are excited to announce a Draft Agenda and our Plenary Speakers. 

• Dates: June 15–17, 2026, in Boulder, CO.
• Registration Link
• Logistics (Links to book a hotel with special rates)

Plenary Speakers: 

Duncan Watson-Parris, Scripps/UCSD - Gradients, benchmarks, and agents: a new toolkit for old uncertainties

Duncan Watson-Parris is an Assistant Professor at Scripps Institution of Oceanography and the Halıcıoğlu Data Science Institute, UC San Diego, where he leads the Climate Analytics Lab. His research focuses on aerosol–cloud interactions and their representation in global climate models, combining satellite observations, machine learning, and differentiable modelling to reduce uncertainty in anthropogenic forcing. He is a lead developer of JEM, the first fully differentiable Earth System Model, and leads the GAIA Initiative at UCSD. His research is supported by an NSF CAREER award, a Google Academic Research Award, and DARPA.

James Done, MMM/NSF NCAR - Advancing Climate Research to Provide Risk-Relevant Hazard Information

James Done leads the Weather Extremes Across Scales research section within NSF NCAR's Mesoscale and Microscale Meteorology Laboratory. He partners with risk managers to advance fundamental understanding of hazards in a changing climate while ensuring that new insights are usable in risk management decision-making. He currently serves on a National Academies Committee on Attribution of Extreme Weather and Climate Events and their Impacts. He is also a member of a US CLIVAR working group on Accelerating Research on the Scientific Foundations of Regional Climate Risk Information.

Cross-Working Group Sessions

On 14-15 June 2026, there are working group sessions designed to share information and encourage discussion and collaboration. We will have four cross-working group sessions this year:

I. Storytelling to craft climate science tools for communities: Explore how storytelling can make CESM data and experiments more engaging and relevant, helping connect research to community needs and inspire new insights.

II.  Harnessing Machine Learning for CESM: Innovation and Integration: Highlight how machine learning is improving CESM, from parameterization to bias correction, while sharing progress, challenges, and future directions.

III. Earth System Prediction with CESM: Bridging Science and Real-World Applications: Focus on CESM-based prediction across timescales and its real-world value, with emphasis on practical applications and new tools to increase impact.

IV. Development and application of high-resolution CESM configurations: Examine advances and challenges in high-resolution CESM modeling, including regional and km-scale simulations across multiple timescales.

Registration opened on April 30, 2026, and will close for in-person participants on Friday, June 5, 2026.

Need more information? Check out our website. 

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New Working Group Co-Chairs and Scientific Steering Committee members

We welcome several new external CESM Working Group co-chairs and a new SSC member to the CESM leadership group.

• Ying Sun, Cornell University, LMWG
• Jung-Eun Lee, Brown University, PWG
• Pierre Gentine, Columbia University, SSC

We thank those who are rotating off, Rosie Fisher (LMWG), Ran Feng (PWG), Samantha Stevenson (PWG), and Sophie Nowicki (SSC), for their many contributions to the CESM activity. See here for the current list of CESM Working Group co-chairs and here for the current SSC membership.  

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2026 Regional Ocean Modeling with MOM6 in the Community Earth System Model Framework

Caption 2025 Crocodile Workshop Participants

Dates: Sep. 28 to Oct. 2, 2026 

Location: NSF NCAR Mesa Laboratory Boulder, CO

Registration

We want YOU to be up and running a regional ocean model, with all the necessary forcing files, boundary conditions, etc., for arbitrary domains and model resolutions, including data assimilation capabilities, in a matter of hours rather than weeks or months! At NSF NCAR and WHOI, as part of the NSF-funded CROCODILE project, we are building Python and Jupyter notebook tools to configure new domains in MOM6 using the Community Earth System Model. Check out our documentation and demos here.

This is our second workshop to showcase capabilities, train new users, and develop collaborations. The first half of the week will guide participants through Jupyter-based tools for configuring and running regional MOM6 in CESM, including automated generation of the model grid and initial and boundary conditions. The latter two days will provide time for participants to develop their own custom domains and develop features in collaboration with the CROCODILE team. This year, we will highlight new capabilities for sea ice, data assimilation, and wave modeling. Last year's agenda can be found here.

The workshop will be held  September 28- October 2, 2026, in person at the NSF NCAR Mesa Lab, Boulder, CO. The deadline to request travel support is July 7, 2026. We can accommodate up to 40 external participants. In the event of receiving additional applications, participants will be selected based on career stage and relevance to their interests and work. Participants from previous years are welcome to attend again to continue collaborating and learn about new tools. Note that new participants will be prioritized over those who have attended in previous years for travel support, and in the event of receiving more applications than available spots.

There is a registration fee of $175; a payment link will be sent to participants not receiving travel support in early September.

Please contact Elizabeth Faircloth, CESM Administrator, with any questions: fair@ucar.edu

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From Earth System Science to Sustainability: A TNC-NCAR Collaboration

On April 22–23, 2026, twenty researchers and practitioners from The Nature Conservancy (TNC) joined twenty scientists from NCAR and UCAR UCP, including several from the CESM community, for a two-day workshop exploring how discoveries in Earth system science could inform solutions across the globe. Using a "World Café" style format, participants rotated through small-group conversations designed to find natural areas of overlap between our organizations. These breakouts sparked individual connections and research questions relevant to both TNC and NCAR.  Workshop-wide discussions included the development of pilot studies, funding opportunities, and datasets. Group-wide discussions helped bring all ideas together into a broader picture of where Earth system science, especially including CESM and other NCAR modeling outputs, could inform decision-making and solutions, as well as how TNC knowledge could advance our Earth system models. As much as it was a scientific exchange, it was also a chance to build genuine relationships across the organizations. Workshop participants were energized by the connections made, and more than 25 potential research ideas and areas of collaboration were identified, along with concrete action items to keep the momentum going.  If you have any questions or comments about the TNC-NCAR collaboration or you would like to get involved, please direct them to Rachel McCrary (rmccrary@ucar.edu).

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Research Highlights from Our Community

Northern Hemisphere Wintertime Teleconnections from the 2023–24 El Niño Offset by Background SST Trends
Clara Deser, Stephen Yeager, Adam S. Phillips, Nan Rosenbloom, and Xueying Zhao

El Niño of 2023–24 ranked among the top five strongest El Niño events of the past 70 years, yet the expected wintertime atmospheric circulation and precipitation impacts over the Northern Hemisphere did not materialize. We investigate the reasons why this was the case and find that effects from long-term trends in tropical sea surface temperatures counteracted the expected El Niño teleconnections. Our results underscore the importance of considering the modulating influence of background sea surface temperatures on El Niño’s fingerprint, especially as anthropogenic climate change accelerates in the coming decades.

An Antarctic ecosystem value index to quantify ecological value across trophic levels and over time
Alice K. DuVivier, Kristen M. Krumhardt, Laura L. Landrum, Zephyr Sylvester, Bilgecan Şen, Sara Labrousse, Christian Che-Castaldo, Alice Eparvier, Marika M. Holland, Michelle A. LaRue, Cara Nissen, Michael N. Levy, Stephanie Jenouvrier & Cassandra Brooks 

The Southern Ocean around Antarctica is one of the fastest-changing regions on the planet and an emerging resource frontier for fisheries. Here, we present the Antarctic Ecosystem Value Index created by merging ecosystem information across food web trophic levels, from phytoplankton to fish and penguins, to quantify the ecological value of marine areas around the Antarctic continent. We find that coastal polynyas - areas of reduced sea-ice - have Index values 31–72% higher than surrounding areas, suggesting that these areas are biologically valuable hot spots for a number of ice-dependent Antarctic Species. Using output from an Earth system model to generate future projections of the Index, we find that high-value locations, often within polynyas, are likely to continue to be valuable throughout the 21st century despite environmental changes. The Antarctic Ecosystem Value Index indicates that penguins lose importance as their habitat becomes increasingly unsuitable, so protecting high-value habitat areas may be critical for these species. This study also shows that while many high-value Index areas are within existing or proposed Marine Protected Areas, there are several opportunities for adopting additional protection, particularly in East Antarctica and the Amundsen Sea.

Reforestation scenarios shape global and regional temperature outcomes
Nora L. S. Fahrenbach, Steven J. De Hertog, Felix Jäger, Peter J. Lawrence & Robert C. Jnglin Wills 

Large-scale reforestation is a prominent proposed climate mitigation strategy, but its full temperature impact remains poorly understood. Here, we present a systematic comparison of temperature responses to three distinct reforestation potentials using a fully-coupled Earth System Model. We find that reforestation consistently provides net global cooling, ranging from −0.13∘C to −0.25∘C, due to carbon uptake partially offset by biogeophysical warming. Crucially, a comparable net global cooling can be achieved with substantially smaller (450 Mha less area) but strategically located reforestation. Reforestation locally cools the tropics but causes albedo-driven warming in higher latitudes, which is often amplified by non-local effects. The different reforestation patterns alone can induce a wide range of non-local effects, showing that planting locations shape the biogeophysical response through atmospheric and oceanic feedbacks. Our findings underscore the importance of climate-smart policies that focus on the geographical placement of reforestation, considering both biogeochemical and biogeophysical effects to maximize cooling benefits.

Emergent climate change signals within Antarctic sea ice and associated ecosystems
Kristen M. Krumhardt, Laura Landrum, Bilgecan Şen, Alice K. DuVivier, Michael N. Levy, Cara Nissen, Marika M. Holland & Stéphanie Jenouvrier 

Antarctic sea ice is projected to decline with continued global climate change, potentially impacting Antarctic ecosystems on several levels. Here, using a series of models, we show that substantial regional and seasonal differences exist in when and how climate change patterns manifest in Antarctic sea ice, phytoplankton, krill, fish, and penguins. Climate-driven changes in fish and penguins tend to emerge from historic variability earlier than sea ice and lower trophic levels. Changes are highly seasonal and can be either negative or positive; for example, krill growth increases in the spring, but decreases in the summer in many regions. The earliest climate signals emerge in Eastern Antarctic regions, while the Ross Sea remains a refuge from climate change into the twenty-first century. In the coming decades, summer sea ice loss in the Weddell Sea could improve the region for fish and krill growth, while remaining habitable for Emperor penguins.

Increased Model Resolution Amplifies Boreal Winter Arctic Precipitation and Atmospheric Circulation Response to Sea Ice Loss
Lantao Sun, Robert C. J. Wills, Clara Deser, Adam Herrington, Isla R. Simpson, and Melissa Gervais

This modeling study examines how increasing model horizontal resolution influences the atmospheric response to future Arctic sea ice loss. Using the Community Earth System Model, version 2.2 (CESM2.2), we conducted two sea ice loss experiments, one with a typical climate model resolution and one with very high resolution over the Arctic, following an experiment protocol similar to the Polar Amplification Model Intercomparison Project (PAMIP). The results show that higher resolution leads to greater increases in Arctic precipitation and its variability in response to sea ice loss. Additionally, the simulations with high resolution over the Arctic exhibit stronger lower-tropospheric temperature and circulation responses over the polar cap compared to the coarser-resolution simulations. These enhanced responses are likely linked to resolution-dependent differences in vertical motion. Our findings advance the understanding of high-resolution modeling and highlight the critical role of horizontal resolution in accurately simulating climate and climate change in the Arctic.

Balancing Backscatter and Diffusion in a 1/4° Forced Global Ocean Model
H. Yassin, G. Marques, I. Grooms

Ocean eddies move heat and nutrients around the globe and shape Earth's climate. Many global climate models now use a quarter-degree grid spacing, where ocean eddies are only partly resolved. At this resolution, older smoothing methods designed to mimic unrepresented eddies now remove too much energy and either eliminate the eddies or make them too weak. One proposed fix is backscatter, which returns some of that lost energy to the flow. We test backscatter in a global ocean–sea ice model and find that simply turning it on everywhere results in excessive heat transport toward the Southern Ocean. We then introduce a simple rule that determines where to smooth eddies and where to return energy, based on how large the eddies are relative to the grid. We test two ways of applying backscatter and find that the model is sensitive to where it is active. Energizing the Southern Ocean increases heat transport, whereas focusing backscatter on western boundary currents mainly strengthens those currents while leaving large-scale Southern Ocean patterns closer to the reference simulation. These findings emphasize the need to understand how backscatter affects heat transport in realistic global ocean models.

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Thanks for reading this CESM Newsletter! Expect to see the next one in the Fall of 2026. Please send potential Newsletter items to Elizabeth Faircloth.