This work documents the first version of the U.S. Department of Energy (DOE) new EnergyExascale Earth System Model (E3SMv1). We focus on the standard resolution of the fully coupled physical model designed to address DOE mission-relevant water cycle questions. Its components include atmosphere and land (110-km grid spacing), ocean and sea ice (60 km in the midlatitudes and 30 km at the equator and poles), and river transport (55 km) models. This base configuration will also serve as a foundation for additional configurations exploring higher horizontal resolution as well as augmented capabilities in the form of biogeochemistry and cryosphere configurations. The performance of E3SMv1 is evaluated by means of a standard set of Coupled Model Intercomparison Project Phase 6 (CMIP6) Diagnosis, Evaluation, and Characterization of Klima simulations consisting of a long preindustrial control, historical simulations (ensembles of fully coupled and prescribed SSTs) as well as idealized CO 2 forcing simulations. The model performs well overall with biases typical of other CMIP-class models, although the simulated Atlantic Meridional Overturning Circulation is weaker than many CMIP-class models. While the E3SMv1 historical ensemble captures the bulk of the observed warming between preindustrial (1850) and present day, the trajectory of the warming diverges from observations in the Key Points: • This work documents E3SMv1, the first version of the U.S. DOE Energy Exascale Earth System Model • The performance of E3SMv1 is documented with a set of standard CMIP6 DECK and historical simulations comprising nearly 3,000 years • E3SMv1 has a high equilibrium climate sensitivity (5.3 K) and strong aerosol-related effective radiative forcing (-1.65 W/m 2 ) Correspondence to: Chris Golaz, golaz1@llnl.gov Citation: Golaz, J.-C., Caldwell, P. M., Van Roekel, L. P., Petersen, M. R., Tang, Q., Wolfe, J. D., et al. (2019). The DOE E3SM coupled model version 1: Overview and evaluation at standard resolution. second half of the twentieth century with a period of delayed warming followed by an excessive warming trend. Using a two-layer energy balance model, we attribute this divergence to the model's strong aerosol-related effective radiative forcing (ERF ari+aci = −1.65 W/m 2 ) and high equilibrium climate sensitivity (ECS = 5.3 K). Plain Language Summary The U.S. Department of Energy funded the development of a new state-of-the-art Earth system model for research and applications relevant to its mission. The Energy Exascale Earth System Model version 1 (E3SMv1) consists of five interacting components for the global atmosphere, land surface, ocean, sea ice, and rivers. Three of these components (ocean, sea ice, and river) are new and have not been coupled into an Earth system model previously. The atmosphere and land surface components were created by extending existing components part of the Community Earth System Model, Version 1. E3SMv1's capabilities are demonstrated by performing a set of standardized simulation experiments described by...

The Energy Exascale Earth System Model Atmosphere Model version 1, the atmospheric component of the Department of Energy's Energy Exascale Earth System Model is described. The model began as a fork of the well‐known Community Atmosphere Model, but it has evolved in new ways, and coding, performance, resolution, physical processes (primarily cloud and aerosols formulations), testing and development procedures now differ significantly. Vertical resolution was increased (from 30 to 72 layers), and the model top extended to 60 km (~0.1 hPa). A simple ozone photochemistry predicts stratospheric ozone, and the model now supports increased and more realistic variability in the upper troposphere and stratosphere. An optional improved treatment of light‐absorbing particle deposition to snowpack and ice is available, and stronger connections with Earth system biogeochemistry can be used for some science problems. Satellite and ground‐based cloud and aerosol simulators were implemented to facilitate evaluation of clouds, aerosols, and aerosol‐cloud interactions. Higher horizontal and vertical resolution, increased complexity, and more predicted and transported variables have increased the model computational cost and changed the simulations considerably. These changes required development of alternate strategies for tuning and evaluation as it was not feasible to “brute force” tune the high‐resolution configurations, so short‐term hindcasts, perturbed parameter ensemble simulations, and regionally refined simulations provided guidance on tuning and parameterization sensitivity to higher resolution. A brief overview of the model and model climate is provided. Model fidelity has generally improved compared to its predecessors and the CMIP5 generation of climate models.

Generating credible climate change and extremes projections remains a high-priority challenge, especially since recent observed emissions are above the worst-case scenario. Bias and uncertainty analyses of ensemble simulations from a global earth systems model show increased warming and more intense heat waves combined with greater uncertainty and large regional variability in the 21st century. Global warming trends are statistically validated across ensembles and investigated at regional scales. Observed heat wave intensities in the current decade are larger than worst-case projections. Model projections are relatively insensitive to initial conditions, while uncertainty bounds obtained by comparison with recent observations are wider than ensemble ranges. Increased trends in temperature and heat waves, concurrent with larger uncertainty and variability, suggest greater urgency and complexity of adaptation or mitigation decisions.climate change ͉ extremes ͉ regional analysis R ecent observations of global-average emissions (1, 2) show higher trajectories than the worst-case A1FI scenario reported in IPCC AR4 (3). Average A1FI temperatures (1, 4) trend higher than the best-case B1 as well as the relatively worse-case A2 scenario (5). Model simulations, validated with observations, have pointed to more intense, longer lasting, and more frequent heat waves in the 21st century (6). However, a rigorous statistical validation of the increased global warming and heat waves, followed by an investigation of the trends at regional scales, is required for decision-makers and end-users. Larger trends in warming and extremes suggest a greater urgency to develop adaptation and mitigation strategies (7,8). On the other hand, a comprehensive assessment of the uncertainties and geographical variability provide an understanding of the tradeoff space for risk-informed decisions (9), which refers to different tactical or strategic options that may be available to a decisionmaker for climate change adaptation and mitigation. Uncertainty of climate model projections has been quantified (10-14) either by comparing model hindcasts with observations or by comparing an ensemble of simulations. However, hindcasts validate models after the fact and hence risk underestimating predictive ability (15), while ensembles may only capture specific aspects of the variability. Hence the reliable and timely analysis of evolving climate model projections, extremes, and uncertainty remains a challenge (16-21). ResultsStatistically Higher Warming Trends. First, we show that the globalaverage temperatures from the middle to end of the 21st century are likely to be higher than previously believed (3). This is suggested by the fact that recent observed emissions trend toward or above A1FI assumptions (1, 2). The fact that observed emissions are at or above the level of A1FI, or any given scenario, in the current decade may not be a compelling reason to support conclusions about temperature in the late 21st century, as the trends could change considerably...

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Fossil fuel combustion and land-use change are the first and second largest contributors to 5 industrial-era increases in atmospheric carbon dioxide concentration, which is itself the 6 largest driver of present-day climate change 1. Projections of fossil fuel consumption and 7 land-use change are thus fundamental inputs for coupled Earth system models (ESMs) 8 used to estimate the physical and biological consequences of future climate system 9 forcing 2,3. While historical datasets are available to inform past and current climate 10 analyses 4,5 , assessments of future climate change have relied on projections of energy and 11 land use from energy economic models, constrained by assumptions about future policy, 12 land-use patterns, and socioeconomic development trajectories 6. Here we show that the 13 influence of biospheric change (i.e., the integrated effect of climatic, ecological, and 14 biogeochemical processes) on land ecosystems drives significant feedbacks in energy,