The correlation between rising levels of CO₂ in the atmosphere (red) at Mauna Loa and rising CO₂ levels (blue) and falling pH (green) in the nearby ocean at Station Aloha. As CO₂ accumulates in the ocean, the water becomes more acidic (the pH declines). (Figure source: modified from Feely et al. 20091ee9bb2b-9b22-48f0-b540-f942ccfd9c71).