Ocean heat content(OHC)change contributes substantially to global sea level rise,so it is a vital task for the climate research community to estimate historical OHC.While there are large uncertainties regarding its value,in this study,the authors discuss recent progress to reduce the errors in OHC estimates,including corrections to the systematic biases in expendable bathythermograph(XBT)data,filling gaps in the data,and choosing a proper climatology.These improvements lead to a better reconstruction of historical upper(0–700 m)OHC change,which is presented in this study as the Institute of Atmospheric Physics(IAP)version of historical upper OHC assessment.Challenges still remain;for example,there is still no general consensus on mapping methods.Furthermore,we show that Coupled Model Intercomparison Project,Phase 5(CMIP5)simulations have limited ability in capturing the interannual and decadal variability of historical upper OHC changes during the past 45 years. Ocean heat content (OHC) change contributes substantially to global sea level rise, so it is a vital task for the climate research community to estimate historical OHC.While there are large uncertainties regarding its value, in this study, the authors discuss recent progress to reduce the errors in OHC estimates, including corrections to the systematic biases in expendable bathythermograph (XBT) data, filling gaps in the data, and choosing a proper climatology. These improvements lead to a better reconstruction of historical upper (0-700 m) OHC change, which is presented in this study as the Institute of Atmospheric Physics (IAP) version of historical upper OHC assessment. Challenges still remain; for example, there is still no general consensus on mapping methods. Futuremore, we show that Coupled Model Intercomparison Project , Phase 5 (CMIP5) simulations have limited ability in capturing the interannual and decadal variability of historical upper OHC changes during the past 45 years.