A4.1 Acidification

CO₂ dissolves in water and forms carbonic acid:

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

More H⁺ means the pH of the water falls. This is called acidification. Sea water is slightly alkaline (pH ≈ 8.2 before the industrial age and ≈ 8.1 now). That small fall of 0.1 pH unit means a 26 % increase in [H⁺] (10^0.1 = 1.26). Acidification is especially harmful to sensitive life stages — eggs and larvae — and to organisms whose enzymes work in a narrow pH range.