ScienceModernglobalhigh confidence

According to NOAA, ocean pH has fallen by 0.1 units over the past 200 years, making ocean waters about 30 percent more acidic.

Notes on verification

Confirmed directly by NOAA and PMEL sources, corroborated by peer-reviewed oceanography literature and Smithsonian Ocean Portal. Minor rounding differences (0.1 vs 0.11) do not undermine the claim. [tier=silver indep_score=0.925 clusters=2 claim_tier=notable]

Sources