Impacts of changes of external forcings from CMIP5 to CMIP6 on surface temperature in FGOALS-g2

Abstract

External forcings among the different phases of the Coupled Model Intercomparison Project (CMIP) vary considerably, but their impacts have not been extensively investigated yet. This study compares the impacts of CMIP5 and CMIP6 forcings on model stability and the 20th-century global warming and El-Nino Southern Oscillation (ENSO) based on the Pre-Industrial control (PI-control) and historical runs of the Flexible Global Ocean-Atmosphere-Land System Model: Grid-point Version 2 (FGOALS-g2). Results indicate that CMIP6 forcings result in a larger climate drift and a lower climatological global average surface temperature (GAST) than those of CMIP5 in PI-control runs. In historical runs, stronger 20th-century warming trends occur during the periods 1910-1940 and 1970-2005 using CMIP6 forcings, which are closer to the HadCRUT than those of the CMIP5 forcings simulation. A stronger spurious warming trend in the CMIP6 results in an evolution of GAST that is less consistent with the HadCRUT dataset than that in the CMIP5 during 1940-1970. Among all forcings, GHGs and aerosol forcings play the dominant roles in differences in GAST, particularly in the Northern Hemisphere. In both the PI-control and historical runs, a larger ENSO amplitude and smaller seasonality are simulated in CMIP6 than in CMIP5.