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: Carbon dioxide is implicated in global warming, sulfur dioxide causes acid rain, and oil spills have polluted our oceans, rivers, and lakes.
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?