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The Community Land Model Urban (CLMU) is an urban parameterization developed to simulate urban climate within a global Earth System Model framework. This paper describes and evaluates parameterization and surface data improvements, and new capabilities that have been implemented since the initial release of CLMU in 2010 as part of version 4 of the Community Land Model (CLM4) and the Community Earth System Model (CESM^®). These include: 1) an expansion of model capability to simulate multiple urban density classes within each model grid cell; 2) a more sophisticated and realistic building space heating and air conditioning submodel; 3) a revised global dataset of urban morphological, radiative, and thermal properties utilized by the model, including a tool that allows for generating future urban development scenarios, and 4) the inclusion of a module to simulate various heat stress indices. The model and data are evaluated using observed data from five urban flux tower sites and a global anthropogenic heat flux (AHF) dataset. Generally, the new version of the model simulates urban radiative and turbulent fluxes, surface temperatures, and AHF as well or better than the previous version. Significant improvements in the global and regional simulation of AHF are also demonstrated that are primarily due to the new building energy model. The new model is available as part of the public release of CLM5 and CESM2.0.

An overview of the Community Earth System Model Version 2 (CESM2) is provided, including a discussion of the challenges encountered during its development and how they were addressed. In addition, an evaluation of a pair of CESM2 long preindustrial control and historical ensemble simulations is presented. These simulations were performed using the nominal 1° horizontal resolution configuration of the coupled model with both the “low‐top” (40 km, with limited chemistry) and “high‐top” (130 km, with comprehensive chemistry) versions of the atmospheric component. CESM2 contains many substantial science and infrastructure improvements and new capabilities since its previous major release, CESM1, resulting in improved historical simulations in comparison to CESM1 and available observations. These include major reductions in low‐latitude precipitation and shortwave cloud forcing biases; better representation of the Madden‐Julian Oscillation; better El Niño‐Southern Oscillation‐related teleconnections; and a global land carbon accumulation trend that agrees well with observationally based estimates. Most tropospheric and surface features of the low‐ and high‐top simulations are very similar to each other, so these improvements are present in both configurations. CESM2 has an equilibrium climate sensitivity of 5.1–5.3 °C, larger than in CESM1, primarily due to a combination of relatively small changes to cloud microphysics and boundary layer parameters. In contrast, CESM2's transient climate response of 1.9–2.0 °C is comparable to that of CESM1. The model outputs from these and many other simulations are available to the research community, and they represent CESM2's contributions to the Coupled Model Intercomparison Project Phase 6.