sentence2_structure: Ocean acidification<>occurs<>when excess carbon dioxide in the atmosphere causes the oceans to become acidic$$$excess carbon dioxide in the atmosphere<>causes<>the oceans to become acidic$$$the oceans<>to become<>acidic
sentence1: Two examples are ocean acidification caused by increased atmospheric concentrations of carbon dioxide, and the long-term melting of ice sheets, which contributes to sea level rise.
sentence2: Ocean acidification occurs when excess carbon dioxide in the atmosphere causes the oceans to become acidic.
question: What occurs when excess carbon dioxide in the atmosphere causes the oceans to become acidic?