Fossil fuels are normally stored in a reservoir deep in the Earth. The carbon in fossil fuels, including coal and oil, are essentially locked out of the natural carbon cycle due to their location deep in the Earth. Humans have found a way to access and utilize this carbon. Identify a risk for accessing this carbon.

Burning fossil fuels moves carbon that was stored underground into the atmosphere, adding carbon dioxide to the natural carbon cycle. A risk is that the atmosphere and climate system may not be able to handle this extra carbon without harmful effects. Choice C, scientists are not sure if the atmosphere can handle all of the excess carbon, describes that risk; plant growth or reduced need for nutrient cycles is not the main concern.

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