The ocean mitigates the extent of global warming by absorbing a portion of the carbon dioxide gas (CO2) released into the atmosphere by human activities. However, this comes at a cost to ocean health because the uptake of this anthropogenic CO2 causes changes in ocean chemistry, called ocean acidification (OA), that can be detrimental to marine ecosystems. This study explores how OA metrics have changed in the upper waters of the open North Pacific Ocean and coastal California Current Large Marine Ecosystem (CCLME). We focus on the CCLME due to its global importance and economically important fisheries. We find that different OA metrics exhibit different patterns of change with depth in the water column due to the natural, background ocean chemistry. One such metric shows that there is now more subsurface water containing CO2 levels elevated enough to threaten the health of marine organisms than there was before the anthropogenic CO2 addition. Our finding of expanded volumes of water with high-CO2 levels near the coast is important to consider as a source of stress for marine organisms living both on the seafloor and in the water column.