Future Weakening of the ENSO Ocean Carbon Buffer Under Anthropogenic Forcing

Abstract

AbstractThe El Niño Southern Oscillation (ENSO) is the largest driver of atmospheric CO2 interannual variability. The equatorial Pacific Ocean, which is a natural source of CO2 to the atmosphere, acts as a buffer of the terrestrial variations by releasing less CO2 during El Niño events and releasing more CO2 during La Niña events. Here, we examine how this ocean carbon buffer will respond to high anthropogenic emissions using Earth system models from Coupled Model Intercomparison Project Phase 6. The models project weaker ocean CO2 flux anomalies in the future due to two main factors: a stronger compensation between thermal and nonthermal changes in ocean biogeochemistry (55% of signal) and a weaker influence of ENSO on the CO2 transfer across the air‐sea interface (10%–25% of signal). The ocean would no longer buffer the land response to ENSO, and could even reinforce its impact on atmospheric CO2, amplifying the atmospheric carbon variability on interannual timescales.