This work focuses on the response in culture experiments to increasing CO₂ of the coccolithophore species Helicosphaera carteri, a unicellular marine calcifying microalgae. The absence of significant changes in coccolith malformations, along with stable size, shape, and calcification-to-photosynthesis ratio, is indicative of H. carteri low sensitivity to CO₂ rise, together with its ability to maintain a stable contribution to the marine rain ratio under future climate changes.