Abstract:OHU (Ocean Heat Uptake) can affect the magnitude of global warming rate and is an important way to measure global warming. By utilizing the experiments of 1% per year increase of CO2 concentration simulated by two coupled models FGOALS-g2 and FGOALS-s2 (hereafter abbreviated g2 and s2), this study assesses and analyses the relationship between OHU and climate sensitivity. The result shows that TCR (transient climate response, i.e., climate sensitivity) in s2 is larger than that in g2, which is mainly related to larger OHU accumulation in the upper ocean, as the larger net heat flux into the ocean in s2 (compared to g2) results in larger OHU as a whole in s2 than in g2. When CO2 is doubled, there are significant differences in spatial distribution of OHU in the two coupled models. The OHU in the upper ocean is significantly larger than that in the deep ocean in s2. In s2, the OHU in the upper ocean is mainly located in the Indian-Pacific Ocean. Different from s2, the OHU difference between the upper ocean and deep ocean is small in g2. The OHU in the deep ocean is mainly located in the Atlantic-Arctic Ocean. Furthermore, the OHU distribution is related to the change in the ocean meridional overturning circulation. The AMOC (Atlantic Meridional Overturning Circulation) in g2 is stronger and deeper than that in s2 in the piControl (Pre-industrial Control) experiment. Meanwhile, the change in the AMOC is relatively small when CO2 is doubled in g2. These changes can bring more heat into the deep ocean and result in increases of OHU in the deep ocean. The averaged AMOC in s2 is weak and shallow in the piControl experiment and weakens significantly when CO2 is doubled. The absorbed heat is retained mainly in the upper ocean, which exerts rapid and strong impacts on the climate sensitivity. Therefore, the OHU change and its spatial distribution induced by ocean circulation affect the climate sensitivity. For this reason, the study of the relationship between OHU and climate sensitivity can help clarifying the uncertainty sources of climate sensitivity.
