Diagnosing global ocean content changes in historically forced CMIP simulations

Formal detection and attribution studies have used observations and climate models to identify an anthropogenic warming signature in the upper (0­700 m) ocean. Recently, as a result of the so-called surface warming hiatus, there has been considerable interest in global ocean heat content (OHC) changes in the deeper ocean, including natural and anthropogenically forced changes evidenced in observational, modelling, and data re-analysis studies. We rely on OHC change estimates from a diverse collection of measurement systems including data from the 19th Century Challenger expedition, a multi-decadal record of ship-based in-situ mostly upper ocean measurements, the more recent near-global Argo floats profiling to intermediate (2000 m) depths, and full-depth repeated transoceanic sections. By diagnosing simulated global OHC changes in historically-forced climate models in three depth layers, we show that the current generation of climate models is broadly consistent with multi-decadal estimates of upper, intermediate (700­-2000 m) and deep (2000 m­ bottom) global OHC changes as well as with Argo-based estimates over the most recent period. Our results suggest that approximately half of the 1860­ present human-caused increases in global ocean heat content may have occurred since 1998.