Artifacts in variations of ocean heat content induced by the observation system changes

Abstract The heat content of the upper ocean is a key climate indicator, contributing to a substantial portion of the global sea level rise. Recent ocean heat content (OHC) calculations have shown a dramatic shift during the period 2001–2003, which is nearly coincident with a major transition in the ocean observation network from a ship‐based system to Argo floats. Here we demonstrate that the changes in the spatial sampling of the historical observation network introduced an artificial jump during the initiation of the global Argo array (2001–2003). The start of the Argo program is responsible for such a shift. Considering the sampling bias, new methods to assess long‐term trends in the OHC (0–700 m) are proposed that suggest the presence of a continuous upper ocean warming (0.36 ± 0.08 W m−2) since 1966.