Future Increase in the All-sky UV-B Radiation over Asia Projected by an Earth System Model

Abstract

Direct simulations of the surface all-sky UV-B radiation in an Earth system model (MIROC-ESM-CHEM) are validated against the operational ground-based measurements of spectral UV radiation at Sapporo, Tateno, Kagoshima, Naha, and Chengkung. The model reasonably reproduces the mean seasonal evolution of the surface UV-B radiation at Sapporo and Naha, but substantially overestimates it at Tateno and Kagoshima during the summer. Underestimation of the cloud effect at these two sites contributes to the overestimation. A projection of the seasonal evolution of the monthly mean UV-B radiation into the future shows a general increase in the 2090s compared to the 2000s. While a slight reduction of the column ozone contributes to the UV-B increase, the effects of the reduction in cloud forcing and, especially, of the reduction in aerosols contribute more significantly. The month for which the largest increase in the UV-B radiation is projected varies site-by-site, reflecting local changes in forcing due to aerosols and clouds.