Based on the information provided, the most likely direct result of increasing levels of atmospheric and oceanic carbon dioxide is:
Many species of marine organisms will be weakened, making them unable to produce and maintain their shells.
This conclusion is drawn from the following key points:
- Increased levels of CO2 lead to more acidic ocean water.
- Acidic water causes calcium carbonate (CaCO3) to dissolve.
- Marine organisms, such as clams, depend on CaCO3 for building their exoskeletons, so a decrease in available CaCO3 due to its dissolution in acidic water would weaken these organisms.