An assessment of climatological ocean temperature and salinity simulated by the CMIP5 climate models

Abstract

A change in ocean circulation can induce a climatic change on a decadal to centennial (or longer) time scale. As a great reservoir of thermal energy, ocean can slowdown (or accelerate) global warming by absorbing (or releasing) thermal energy from (or to) the atmosphere. Thus, climate models’ capability to simulate the ocean is important for climate modeling and future climate projection. Evaluation of ocean modelling for a climate change, however, has been largely done for the surface values or for specific regions, or it has been often done only for a small number of models. The purpose of this study is to make an assessment of CMIP5 (fifth phase of Coupled Model Intercomparison Project) climate models on the climatological mean ocean temperature and salinity.Using 38 climate models, we constructed a multi-model ensemble (MME) and compared the climatological annual means for the 30 years from 1975 to 2004 with an ocean reanalysis dataset, EN4. The CMIP5 MME mean (MMM) shows a warm bias overall in the Pacific, Atlantic, Southern and Indian Ocean basins, but a cold bias partly in the upper level of the Pacific and Atlantic basins and in the intermediate level of northern Indian Ocean. The MMM shows a warm bias overall in the Atlantic Ocean from the surface to a deep ocean. It is notable that the largest bias in temperature profile corresponds to the depth of a maximum bias in salinity, where a vertical gradient isgy from (or to) the atmosphere. Thus, climate models’ capability to simulate the ocean is important for climate modeling and future climate projection. Evaluation of ocean modelling for a climate change, however, has been largely done for the surface values or for specific regions, or it has been often done only for a small number of models. The purpose of this study is to make an assessment of CMIP5 (fifth phase of Coupled Model Intercomparison Project) climate models on the climatological mean ocean temperature and salinity.Using 38 climate models, we constructed a multi-model ensemble (MME) and compared the climatological annual means for the 30 years from 1975 to 2004 with an ocean reanalysis dataset, EN4. The CMIP5 MME mean (MMM) shows a warm bias overall in the Pacific, Atlantic, Southern and Indian Ocean basins, but a cold bias partly in the upper level of the Pacific and Atlantic basins and in the intermediate level of northern Indian Ocean. The MMM shows a warm bias overall in the Atlantic Ocean from the surface to a deep ocean. It is notable that the largest bias in temperature profile corresponds to the depth of a maximum bias in salinity, where a vertical gradient is