Assessment of the global ocean heat content and North Atlantic heat transport over 1993–2020

Abstract

Understanding changes in global ocean heat content (OHC) is essential for investigating Earth’s energy imbalance and climate change. OHC trends are assessed using four state-of-the-art ocean reanalyses and one objective analysis. The spatial OHC trend patterns captured by reanalyses are consistent with each other, but sensitive to the selected time period. A higher proportion of heat uptake in the 100–2000 m sub-surface layer over 2001–2010 than 1994–2000 contributed to the temporary slowdown in global surface warming. The North Atlantic meridional overturning circulation (MOC) and heat transport show better agreement with RAPID observations compared with previous studies. Zonal mean OHC trends in the North Atlantic over 40–60 °N differ for the MOC increasing (2000–2004) and decreasing periods (2005–2010) and OHC increases are more concentrated between 30 and 40 °N in the later MOC increasing period (2011–2022). These results do not support previous studies suggesting that MOC changes are reducing Earth’s mean surface warming.