Why do atmospheric carbon dioxide levels rise and fall seasonally measured on Mauna Loa? This study explores the thermal calcification (TC) hypothesis, suggesting that seasonal temperature shifts in surface seawater cause acid pH-driven CO₂ emissions triggered by calcification. Using oceanographic data, we modeled how temperature affects dissolved inorganic carbon including CO₂, bicarbonate, and carbonate [1]. Our findings suggest that warming waters absorb atmospheric CO2 by promoting calcium carbonate formation, lowering mixing zone seawater pH and boosting CO₂ release to the atmosphere in late autumn and winter, when atmospheric CO₂ becomes highest. The model predicts a net annual CO₂ rise of 2 ppmv, driven by calcification rather than land-based processes. Seasonal pH swings of 0.04 units corroborate this mechanism. Kennanook/Cape Grim seasonal oscillations are less pronounced, possibly a result of nearby seawater having a deeper mixing zone and fewer nutrients for seasonal calcification but still allowing net CO2 annual emissions to the troposphere. The TC hypothesis indicates that continued ocean warming, not only fossil-fuel emissions, contribute to rising atmospheric CO₂ levels [2], calling for deeper investigation into marine carbon dynamics.