Effects of Anthropogenic Forcings on Multidecadal Variability of the Sea Level around the Japanese Coast Simulated by MRI‐ESM2.0 for CMIP6

The observed sea level (SL) around the Japanese coast shows a peculiar multidecadal variation with the peak in the 1950s followed by the gradual fall until the 1970s and the rebound continuing to the present, making the recent SL rise less remarkable in the historical record. The multidecadal SL variability of an ensemble mean of the Coupled Model Intercomparison Project phase 6 historical simulations using the Meteorological Research Institute Earth System Model version 2.0 (MRI-ESM2.0) compares well with the observation and is greater than the piControl one, implying the observed variability could be a forced one. The MRI-ESM2.0 simulations for the Detection and Attribution Model Intercomparison Project suggest the increase in anthropogenic aerosols and greenhouse gases caused the fall and rise of the SL, respectively. Additional sensitivity runs indicate the surface heat loss in the North Pacific due to anthropogenic aerosols plays a dominant role in the SL fall. Plain Language Summary The coastal sea level (SL) change is important because it significantly affects human activity. It is known that the SL around Japan fell from the 1950s to the 1970s and rose from the 1980s. However, the reason for this long-term SL change around Japan has not been well understood. In this study, the SL around Japan in a suite of simulations by a climate model, the Meteorological Research Institute Earth System Model version 2.0, is analyzed and the cause of the SL change is investigated. In the historical simulations of the climate model, both the SL fall from the 1950s to the 1970s and the SL rise from the 1980s occur around Japan. From the analysis of the sensitivity simulations to separately evaluate effects of anthropogenic forcings, it is suggested that the increase in anthropogenic aerosols caused the SL fall and that in greenhouse gases caused the SL rise. Especially, surface heat loss in the North Pacific due to anthropogenic aerosols is likely to have a dominant role in the SL fall.