Time of Emergence Large Ensemble Intercomparison for Ocean Biogeochemistry and Observerables

The contemporary ocean carbon sink is an important mitigator of global warming and the dominate driver of ocean acidification. Detecting future changes in the ocean carbon sink and its constituent pumps requires quantification of not only the magnitude of the change (anthropogenic signal) but also the natural background variability inherent to the climate system (noise). Here we use Large Ensemble (LE) experiments from 4 Earth System Models to estimate the Time of Emergence (ToE) for anthropogenic signals in the ocean carbon cycle, partition uncertainty in future projections of the ocean carbon cycle, and for the first time, quantify the model sensitivity of internal variability in the ocean carbon cycle. For sea surface temperature (SST) and air-sea CO₂ fluxes, the LEs agree on global and regional ToE ( 20 - 30 years, with the exception of the Southern Ocean), despite model differences in the magnitude of warming and ocean carbon uptake. For the biological carbon pumps, ToEs estimates are 50+ years and differ (by multiple decades) between the LEs. Finally, as an emergent constraint on ToE estimates, we utilize data-based products to validate LE natural decadal variability.