Traditionally, ocean acidification researchers have focused on how secular changes in carbon dioxide (CO2) or pH will impact organisms. Global mean pH is estimated to have decreased by 0.1 pH units (representing a 28% increase in acidity) since the preindustrial age and may drop another 0.3 pH units by the end of this century (1). Several recent papers, however, have highlighted the importance of understanding changes in the short-term variability in carbon parameters in addition to the secular trends (2⇓–4). An article in PNAS by Pacella et al. (5) examines how net community metabolism (NCM) in a coastal seagrass bed can help slow the long-term secular change in ocean acidification but exacerbates the short-term variations in carbon system parameters. These short-term variations can drive the pH or the saturation state of the waters with respect to aragonite below a threshold for certain organisms that may prevent them from ever benefitting from the long-term relief.