Constraining the trend in the ocean CO₂ sink during 2000-2022.

Abstract

The ocean will ultimately store most of the CO₂ emitted to the atmosphere by human activities. Despite its importance, estimates of the 2000-2022 trend in the ocean CO₂ sink differ by a factor of two between observation-based products and process-based models. Here we address this discrepancy using a hybrid approach that preserves the consistency of known processes but constrains the outcome using observations. We show that the hybrid approach reproduces the stagnation of the ocean CO₂ sink in the 1990s and its reinvigoration in the 2000s suggested by observation-based products and matches their amplitude. It suggests that process-based models underestimate the amplitude of the decadal variability in the ocean CO₂ sink, but that observation-based products on average overestimate the decadal trend in the 2010s. The hybrid approach constrains the 2000-2022 trend in the ocean CO₂ sink to 0.42 ± 0.06 Pg C yr^-1 decade^-1, and by inference the total land CO₂ sink to 0.28 ± 0.13 Pg C yr^-1 decade^-1.