Observed Multi‐Decadal Acceleration of Globally Averaged Abyssal Ocean Warming

Abstract Given sparse historical data in the deep and abyssal ocean, previously only multi‐decadal temperature trends have been estimated from observations there on a global scale. Full‐depth CTD sampling started circa 1970, with the first decadal global ship‐based survey occupied in the 1990s, and the first regional pilot array of Deep Argo floats started circa 2016. Here we fit second‐order polynomial functions versus time to all available full‐depth CTD profile temperature data in local spatial bins to estimate changes in the rates of these multi‐decadal temperature trends. We find a statistically significant increase of the heating rate of the abyssal (4,000–6,000 dbar) ocean, from 5.4 (±4.9) TW in 1988 to 20.2 (±3.9) TW in 2018. In contrast, we find no statistically significant change in the heating rate of the deep ocean, estimated at 29.4 (±22.1) TW in 1988 and 25.0 (±17.5) TW in 2018.