Interactive Gas Chemistry for Enhanced Science Capabilities of the Energy Exascale Earth System Model Version 3

Abstract Atmospheric chemistry plays a crucial role in Earth system models (ESMs), controlling atmospheric composition and radiative balance; it is highly interactive with the physical climate, biogeochemical cycles, and human systems. However, it often imposes computational challenges in an ESM. Here we develop a full troposphere‐stratosphere interactive chemistry module for the US Department of Energy's Energy Exascale Earth System Model (E3SM). We intentionally build a streamlined module based on E3SM version 2 that interacts with other components and maintains all of major chemical and chemistry‐climate feedbacks. The module incorporates a new, highly efficient tracer advection scheme; linearization of stratospheric chemistry; and abridged tropospheric chemical mechanism with 28 reactive tracers. This new model, E3SM‐chem, can readily perform century‐long climate simulations of ozone, methane, and nitrous oxide based on emission scenarios as well as provide hourly budgets for the gas‐phase radicals that drive aerosol chemistry. We evaluate E3SM‐chem with an atmosphere‐only simulation as in the recent climate model intercomparison project (CMIP6) finding results similar to the other CMIP6 models. For the present‐day, E3SM‐chem matches the standard measurement metrics for stratospheric and tropospheric ozone, surface air quality, other key reactive gases like carbon monoxide, and the methane lifetime. Overall, E3SM‐chem maintains the climate fidelity of the baseline model while adding at most 20% to the computational cost of the atmosphere model. Hence, interactive chemistry can be a default configuration for long climate simulations at resolutions of 1° or finer, which is crucial for producing self‐consistent chemistry‐climate feedbacks that alter the climate system.Plain Language Summary We have developed an interactive atmospheric chemistry module for version 3 of the US Department of Energy's Energy Exascale Earth System Model (E3SM). This new chemistry module significantly enhances E3SM's ability to simulate chemistry‐climate interactions, thereby representing climate processes more accurately. Importantly, these advancements were achieved without compromising the existing climate simulation in quality or computational cost, thus allowing for the capture of self‐consistent chemistry‐climate evolution both in historical periods and future scenario projections allowing atmospheric composition to respond naturally to changing emissions.Key Points A streamlined interactive atmospheric chemistry module has been developed for Earth system model (ESM) version 3 The new module does well on standard atmospheric trace gas metrics while maintaining or improving the existing climate simulation The chemistry package improves E3SM's science capabilities (chemistry‐climate feedbacks, air quality) with minimal added computational cost