What is ocean acidification primarily caused by?

Ocean acidification is primarily caused by the absorption of carbon dioxide (CO2) by the oceans. As atmospheric carbon dioxide levels rise through human activities, particularly fossil fuel combustion and deforestation, a significant portion of this carbon dioxide is absorbed by seawater. When CO2 dissolves in water, it reacts chemically to form carbonic acid, which then dissociates into bicarbonate and hydrogen ions. The increase in hydrogen ions leads to lower pH levels in the ocean, indicating increased acidity. This process can harm marine organisms, particularly those with calcium carbonate structures, such as corals and shellfish, disrupting marine ecosystems.

While increased temperatures (another choice) can have various effects on marine environments, they are not the direct cause of acidification itself. Pollution from plastics and overfishing impact marine life and ecosystems but do not have a direct role in altering the ocean's acidity levels in the same manner as carbon dioxide absorption does.