Assessment of future changes in the sea surface temperature in the Northwest Pacific projected by CMIP6 models

Abstract

Coupled Model Intercomparison Project Phase 6 (CMIP6) models project more rapid warming compared with CMIP5. However, CMIP6 models still have considerable inter-model differences for future sea surface temperature (SST) projection. In this study, we examine SST biases in the Northwest Pacific (NwP) simulated by 27 CMIP6 models and evaluate future changes in the SST under both the lower emission scenario (SSP1-2.6) and higher emission scenario (SSP5-8.5) projected by the selected seven CMIP 6 models based on their performance. The selected seven models were ACCESS-ESM1-5, CanESM5, EC-Earth3, KACE-1-0-G, MPI-ESM1-2-HR, MRI-ESM2-0, and UKESM1-0-LL. The SST in the NwP is projected to increase by approximately 1.8°C for SSP1-2.6 and 4.5°C for SSP5-8.5. Noticeably, the projected SST changes are greater in summer (August) than in winter (February) under SSP5-8.5. The stronger surface warming in summer are primarily attributed to thinning of the summer shallow mixed layer. The inter-model difference in the future SST changes is considerably large in the mixed water region (interfrontal zone) between Kuroshio and Oyashio, suggesting less reliability in future projection in the region.