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Extreme precipitation events are driven by complex multiscale atmospheric dynamic interactions, fuelled by available moisture. They are expected to intensify with climate change, posing increasing risks to human communities and ecosystems. However, current low-resolution climate models struggle to accurately represent key extreme precipitation-generating phenomena, limiting our ability to generate robust and reliable future projections. Here we present an ensemble of climate simulations with a 10-to-25-km resolution and an improved representation of mesoscale convective systems to assess future changes in daily extreme precipitation and its drivers. Our high-resolution simulations more realistically capture the observed spatial distribution and intensity of daily extreme precipitation over the historical period than the 100-km resolution counterparts. In a future scenario with high carbon dioxide emissions, daily extreme precipitation over land could increase by about 41% by 2100, mainly as a result of increased mesoscale moisture convergence. The impact of this dynamical contribution to extreme precipitation is underestimated by a factor of three in the low-resolution model. These results highlight the crucial role of high-resolution climate modelling in constraining future extremes and informing more effective climate risk assessments and adaptation strategies. 

Accurate prediction of sea surface temperatures (SSTs) in the tropical North Atlantic on multiyear timescales is of paramount importance due to its notable impact on tropical cyclone activity. Recent advances in high-resolution climate predictions have demonstrated substantial improvements in the skill of multiyear SST prediction. This study reveals a notable enhancement in high-resolution tropical North Atlantic SST prediction that stems from a more realistic representation of the Atlantic Meridional Mode and the associated wind-evaporation-SST feedback. The key to this improvement lies in the enhanced surface wind response to changes in cross-equatorial SST gradients, resulting from Intertropical Convergence Zone bias reduction when atmospheric model resolution is increased, which, in turn, amplifies the positive feedback between latent and sensible surface heat fluxes and SST anomalies. These advances in high-resolution climate prediction hold promise for extending tropical cyclone forecasts at multiyear timescales. 

{"Abstract":["The original "CESM2 Tuned Sea Ice Albedo" experiments were run to investigate the impact of sea ice snow albedo tuning on Arctic mean state and global responses. These simulations were run by David Bailey, and the results were written up in Kay et al. 2022 [https://doi.org/10.1029/2021MS002679]. These were configured the same as the standard CMIP6 runs, but with adjusted r_snw=1.5 and dt_mlt=1.0 in the sea ice model (cice) namelist. (For local disk access, these data are all in the main directory and are not separated by case name.)Original experimentsControl run: b.e21.B1850.f09_g17.CMIP6-piControl.001_branch2 * Data are generally available years 811-1350 * These runs are fully coupled * Monthly Ocean, Sea Ice, and Atmosphere variables are availableHistorical runs: b.e21.BHIST.f09_g17.CMIP6-historical.01? * There are four ensemble members * Ensemble number 012 started in 1850 and ran to 2015 * Ensemble numbers 013, 014, 015 start in 1920, branched from ensemble 012 with a pertlim, and go to 2015 * These runs are fully coupled * Monthly Ocean, Sea Ice, and Atmosphere variables are availableFuture runs: b.e21.BSSP370cmip6.f09_g17.CMIP6-SSP3-7.0.? * The first three SSP runs (012,013,014) were configured the same as the CMIP6 scenario runs, but there was a bug in the future forcing * New runs were then done with the updated forcing (112, 113, 114, 115, 116) * The runs use standard CMIP6 SSP370 standard forcing, start in 2015 and go through 2100 * These runs are fully coupled * Monthly Ocean, Sea Ice, and Atmosphere variables are availableThere are also some experiments that are not fully coupled experiments: * e.e21.E1850.f09_g17.CMIP6-piControl.* * d.e21.f09_g17.{001,002,003,004,005}Additional ExperimentsThe additional CESM2 Tuned Sea Ice Albedo experiments were run to extend the dataset and include more frequent (daily) output as well as some modifications to the external forcing. This was done as part of a NSF Navigating the New Arctic (NNA) project (NSF #1928119): NNA Track 1: Collaborative Research: Maritime transportation in a changing Arctic: Navigating climate and sea ice uncertainties. These simulations were run by Alice DuVivier, and the data will be used in various studies. (For local disk access, these data are all in the main directory and are separated by case name.)Historical runs: b.e21.BHISTsmbb.f09_g17.CMIP6-historical.1? * There are five ensemble members: 118, 119, 120, 121, 122 * These ensembles start in 1990 and run through 2015 * These use smoothed biomass burning forcing (smbb), which uses the smoothed biomass burning forcing starting the 1990s. Information about the smoothed biomass burning impacts can be found in DeRepentigny et al. 2022 [https://doi.org/10.1126/sciadv.abo2405] * These runs are fully coupled * Daily and Monthly Ocean, Sea Ice, and Atmosphere variables are available * Restart files are also available upon request to co-authorsFuture runs: b.e21.BSSP370cmip6.f09_g17.CMIP6-SSP3-7.0.2? * There are five ensemble members: 218, 219, 220, 221, 222 * The runs use standard CMIP6 SSP370 standard forcing, start in 2015 and go through 2100. They are continued from the SMBB historical runs (above) * These runs are fully coupled * Daily and Monthly Ocean, Sea Ice, and Atmosphere variables are available * Restart files are also available upon request to co-authors * These runs were done on the Derecho supercomputer (instead of Cheyenne, which was used for all the above experiments)"]} 

Abstract Upwelling along ocean eastern boundaries is expected to intensify due to coastal wind strengthening driven by increasing land-sea contrast according to the Bakun hypothesis. Here, the latest high-resolution climate simulations that exhibit drastic improvements of upwelling processes reveal far more complex future upwelling changes. The Southern Hemisphere upwelling systems show a future strengthening in coastal winds with a rapid coastal warming, whereas the Northern Hemisphere coastal winds show a decrease with a comparable warming trend. The Bakun mechanism cannot explain these changes. Heat budget analysis indicates that temperature change in the upwelling region is not simply controlled by vertical Ekman upwelling, but also influenced by horizontal heat advection driven by strong near-coast wind stress curl that is neglected in the Bakun hypothesis and poorly represented by the low-resolution models in the Coupled Model Intercomparison Project. The high-resolution climate simulations also reveal a strong spatial variation in future upwelling changes, which is missing in the low-resolution simulations. 

Abstract The impact of increased model horizontal resolution on climate prediction performance is examined by comparing results from low-resolution (LR) and high-resolution (HR) decadal prediction simulations conducted with the Community Earth System Model (CESM). There is general improvement in global skill and signal-to-noise characteristics, with particularly noteworthy improvements in the eastern tropical Pacific, when resolution is increased from order 1° in all components to order 0.1°/0.25° in the ocean/atmosphere. A key advance in the ocean eddy-resolving HR system is the reduction of unrealistic warming in the Southern Ocean (SO) which we hypothesize has global ramifications through its impacts on tropical Pacific multidecadal variability. The results suggest that accurate representation of SO processes is critical for improving decadal climate predictions globally and for addressing longstanding issues with coupled climate model simulations of recent Earth system change. 

Abstract. This work assesses a recently produced 21-member climate model large ensemble (LE) based on the U.S. Department of Energy's Energy Exascale Earth System Model (E3SM) version 2 (E3SM2). The ensemble spans the historical era (1850 to 2014) and 21st century (2015 to 2100), using the SSP370 pathway, allowing for an evaluation of the model's forced response. A companion 500-year preindustrial control simulation is used to initialize the ensemble and estimate drift. Characteristics of the LE are documented and compared against other recently produced ensembles using the E3SM version 1 (E3SM1) and Community Earth System Model (CESM) versions 1 and 2. Simulation drift is found to be smaller, and model agreement with observations is higher in versions 2 of E3SM and CESM versus their version 1 counterparts. Shortcomings in E3SM2 include a lack of warming from the mid to late 20th century, likely due to excessive cooling influence of anthropogenic sulfate aerosols, an issue also evident in E3SM1. Associated impacts on the water cycle and energy budgets are also identified. Considerable model dependence in the response to both aerosols and greenhouse gases is documented and E3SM2's sensitivity to variable prescribed biomass burning emissions is demonstrated. Various E3SM2 and CESM2 model benchmarks are found to be on par with the highest-performing recent generation of climate models, establishing the E3SM2 LE as an important resource for estimating climate variability and responses, though with various caveats as discussed herein. As an illustration of the usefulness of LEs in estimating the potential influence of internal variability, the observed CERES-era trend in net top-of-atmosphere flux is compared to simulated trends and found to be much larger than the forced response in all LEs, with only a few members exhibiting trends as large as observed, thus motivating further study. 

Biomass burning aerosol (BBA) emissions in the Coupled Model Intercomparison Project phase 6 (CMIP6) historical forcing fields have enhanced temporal variability during the years 1997–2014 compared to earlier periods. Recent studies document that the corresponding inhomogeneous shortwave forcing over this period can cause changes in clouds, permafrost, and soil moisture, which contribute to a net terrestrial Northern Hemisphere warming relative to earlier periods. Here, we investigate the ocean response to the hemispherically asymmetric warming, using a 100-member ensemble of the Community Earth System Model version 2 Large Ensemble forced by two different BBA emissions (CMIP6 default and temporally smoothed over 1990–2020). Differences between the two subensemble means show that ocean temperature anomalies occur during periods of high BBA variability and subsequently persist over multiple decades. In the North Atlantic, surface warming is efficiently compensated for by decreased northward oceanic heat transport due to a slowdown of the Atlantic meridional overturning circulation. In the North Pacific, surface warming is compensated for by an anomalous cross-equatorial cell (CEC) that reduces northward oceanic heat transport. The heat that converges in the South Pacific through the anomalous CEC is shunted into the subsurface and contributes to formation of long-lasting ocean temperature anomalies. The anomalous CEC is maintained through latitude-dependent contributions from narrow western boundary currents and basinwide near-surface Ekman transport. These results indicate that interannual variability in forcing fields may significantly change the background climate state over long time scales, presenting a potential uncertainty in CMIP6-class climate projections forced without interannual variability.