CO₂ dissolves into seawater and reacts: CO₂ + H₂O ⇆ H₂CO₃ ⇆ H⁺ + HCO₃⁻. The released H⁺ ions lower pH and react with carbonate ions (CO₃²⁻), leaving less available for shell-building organisms.
This simulator uses pH ≈ 8.17 − 0.29 × ln(CO₂/280) and a simplified aragonite saturation state Ω = 4.0 × e−(CO₂−280)/650. Ω > 1 favours shell growth; below 1, seawater turns corrosive and existing shells dissolve faster than they form.
Pre-industrial CO₂ was 280 ppm; today it is above 420 ppm. Pteropods, corals and other calcifiers are already showing thinner, pitted shells as Ω falls.