Uncertainties in solar radiation assessment in the United States using climate models

Abstract

Solar energy is abundant and offers significant potential for future climate change mitigation. This study investigates the impacts of climate change on surface solar radiation in the United States using a set of climate projections from global and regional climate models (GCMs and RCMs). Multi-model ensemble mean of GCMs in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) show a significant increase in annual mean surface solar radiation over the eastern and southern US. The projected solar brightening is consistent among different future periods and pathways. However, RCMs in North American Coordinated Regional Climate Downscaling Experiment (NA-CORDEX) and convection-permitting simulations of the climate of North America exhibit a significant decrease in surface solar radiation over large areas of the US. Those conflicting responses between the GCMs and RCMs are evident throughout the year with the greatest disagreement during fall. When scrutinizing the mechanism of solar radiation changes, we find that cloud behavior alone cannot adequately explain the contrasting changes in solar radiation. Instead, if a climate model considers transient aerosols is the key for solar brightening or dimming. Future solar brightening is mainly associated with the declining aerosols that have been implemented in most of the CMIP5 GCMs. In contrast, solar dimming becomes evident because of the greenhouse gas effects in those GCMs and RCMs without considering the aerosol effects. This study highlights the importance of the aerosol effects in solar energy-related climate assessment, and it is necessary to implement the aerosol forcing in regional climate downscaling.