Cloud response to aerosols and surface warming are major uncertainty in predicting the evolution of the Earth system. The uncertainty is commonly attributed to deficiencies in Earth system models (ESMs), including, but not limited to, coarse model resolution, overly simplified process representations, and a lack of strong observational constraint. Using a strategy that focuses on improving clouds in the Energy Exascale Earth System Model (E3SM), we find that the atmosphere manifests itself to reduce biases in other aspects of the system. The more realistic model produces lower sensitivity to aerosol perturbation, suggesting potential improvements to the historical evolution of surface temperature over EAMv1. Climate and cloud feedbacks are also significantly reduced in the recalibrated model, which leads to a lower climate sensitivity. A perturbed physics ensemble (PPE) reveals that cloud feedback processes are partly coupled, and partly decoupled, from aerosol-cloud interactions. To improve our confidence in, and understanding of, the role of aerosol-cloud interactions, our ongoing model development efforts focus on redesigning the aerosol, cloud microphysics, macrophysics, and turbulence parameterizations for global convection-permitting simulations envisioned for E3SMv4. These model development efforts are routinely informed by observations to ensure improved realism in both process and system levels.
Dr. Po-Lun Ma is an Earth scientist at the Pacific Northwest National Laboratory (PNNL). He earned his Ph.D. from Johns Hopkins University in 2010 and joined PNNL soon after his graduation. His research mainly focuses on aerosol-cloud-climate interactions, climate model evaluation, and uncertainty quantification. In the U.S. Department of Energy's Accelerated Climate Modeling for Energy (ACME) project, Dr. Ma was singled out for "Serving as the critical link between developers, integrators, and task leaders to tune and validate the atmosphere and coupled ACME v1 systems." Because of his excellent accomplishments and contributions, Dr. Ma was honored with Exceptional Contribution Program Awards by PNNL in 2013 and again 2014 in addition to an Outstanding Contribution Award for the ACME project in 2016.