paleoWeather: iCESM1.3-HR simulations with water isotopes for the mid-Piazencian Warm Period

The paleo Weather: high-resolution Community Earth System Model version 1.3 (iCESM1.3 HR) simulation of the mid-Piacenzian Warm Period (~3 million years ago) dataset is a member of a paleo Weather collection that represents the first high-resolution paleoclimate simulation suite of this kind made available to the community. Its horizontal grid spacing is approximately ten times finer than traditional climate-model configurations, which typically use resolutions of 1-2°. The CESM-HR resolution more realistically represents synoptic- and mesoscale atmospheric and oceanic phenomena, together with their interactions with large-scale circulation. The mid-Piacenzian Warm Period dataset will support research on weather-climate interactions in a warm-climate state, including studies of extreme events such as heat waves, atmospheric rivers, and tropical cyclones. More broadly, the paleo Weather simulations complement the MESACLIP historical and future simulations, providing opportunities to investigate links between climate and weather extremes across Earth's past, present, and future climate states.

Supported by an Accelerated Scientific Discovery (ASD) Derecho computing grant, our research team consisting of scientists and software engineers at the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR) and the Universities of Connecticut and Arizona completed an unprecedented CESM-HR simulation of the mid-Piacenzian Warm Period (~3 million years ago). The high-resolution simulation includes water isotope capability, enabling direct comparisons with isotope records of past and present climate change from a range of archives. The simulation followed the protocols of the Pliocene Model Intercomparison Project (PlioMIP2) and was run with atmospheric CO2 concentrations of 400 ppmv inferred from the geological record. The simulation was initialized from a near-equilibrated, low-resolution companion simulation and integrated for 60 years.

The paleo Weather experiments employed the scientifically validated and widely used Community Earth System Model version 1.3 with high-resolution capabilities (CESM1.3 HR). CESM1.3 HR uses the same model components as the CESM1.1, the version that contributed to the Coupled Model Intercomparison Project Phase 5 (CMIP5) and has been used in several large-ensemble projects. The model components include the Community Atmospheric Model (CAM5.3), the Community Land Model (CLM4), the Parallel Ocean Program (POP2), and the Community Ice Sheet Model (CICE4). Relative to CESM1.1, CESM1.3 HR includes bug fixes in the radiation and cloud microphysics schemes, as well as software infrastructure updates that enable high-resolution applications. In this configuration, the atmosphere and land components are run at ~0.25° horizontal resolution, while the ocean and sea-ice components are run at approximately ~0.1°, representing nearly an order-of-magnitude increase in resolution compared with the more traditional 1° configuration. To accommodate these resolution refinements, resolution-dependent tuning is applied in the atmosphere and sea ice to achieve a realistic preindustrial climate state and radiative balance.

The mid-Piacenzian Warm Period dataset is one of four high-resolution simulation datasets produced through the ASD paleo Weather project, enabling discovery and comparison across time periods. The other ASD paleo Weather datasets represent the Preindustrial (PI, 1850 CE), Last Glacial Maximum (LGM, 21 kyr ago), and two Early Eocene Climatic Optimum (EECO, ~53-50 million years ago). Also available are the MESACLIP dataset with CESM1.3 HR simulations (without water isotopes) for the preindustrial, historical period, RCP2.6, RCP4.5, RCP6.0, and RCP8.5.

Citation: The papers linked below are relevant references for the iCESM1.3-HR ensemble. Otto-Bliesner et al. (2026a) describes the suite of five paleo Weather simulations: boundary conditions and forcing, initialization, years and variable definitions, and resources for analysis. Otto-Bliesner et al. (2026b) utilizes the high-temporal-resolution output across the suite of experiments to evaluate changes in past extreme weather events. Please cite the dataset citation in any documents or publications that use these data, along with the associated paper(s) most relevant to your research. We would also appreciate receiving a copy of the relevant publications. This will help us to justify keeping the data freely available online in the future. Thank you!