The California Current System (CCS) sustains economically valuable fisheries and is particularly vulnerable to ocean acidification, due to the natural upwelling of corrosive waters that affect ecosystem function. Marine resource managers in the CCS could benefit from advanced knowledge of ocean acidity on multiyear timescales. We use a novel suite of retrospective forecasts with an initialized Earth system model (ESM) to predict the evolution of surface pH anomalies in the CCS. Here we show

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... the forecast system skillfully predicts observed surface pH variations multiple years in advance over a naïve forecasting method. Skillful predictions of surface pH are mainly derived from the initialization of dissolved inorganic carbon anomalies that are subsequently transported into the CCS. Our results demonstrate the potential for ESMs to provide predictions relevant to managing the onset and impacts of ocean acidification in this vulnerable region.