Detecting the anthropogenic influences on recent changes in ocean carbon uptake

Anthropogenic greenhouse gas emissions have modified the rate at which oceans have absorbed atmospheric CO2 over the last centuries through rising atmospheric CO2 and modifications in climate. However, there are still missing pieces in our understanding of the recent evolution of air-sea CO2 exchanges related to the magnitude of their response to anthropogenic forcings versus that controlled by the internal variability. Here, to detect and attribute anthropogenic influences on oceanic CO2 uptake between 1960 and 2005, we compare an ensemble of Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model simulations forced by individual drivers to ocean-only model reconstructions. We demonstrate that the evolution of the global oceanic carbon sink over the last decades can be understood without invoking climate change, attributing rising atmospheric CO2 as prominent driver of the oceanic sink. Nonetheless, at regional scale, the influence of climate change on air-sea CO2 exchanges seems to emerge from the internal variability within the low-latitude oceans.

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