When we think about the carbon cycle and human activities, it is important to differentiate between facts and hypotheses. Which of the following is NOT a fact, but is a hypothesis? A. The amount of carbon dioxide in the atmosphere has increased since 1950. B. Increasing atmospheric carbon dioxide will cause mean global temperature to increase by 2 degrees Celsius over the next century. C. The burning of fossil fuels contributes substantially to the ongoing rise of atmospheric CO2. D. In the past, atmospheric CO2 levels reached levels higher than those observed today.

B. Increasing atmospheric carbon dioxide will cause mean global temperature to increase by 2 degrees Celsius over the next century.

Explanation:

By definition, a hypothesis is a tentative statement or prediction with little or no experimental test. Hypotheses are always formulated such that they can be rejected if experimental findings are against them.

Hypotheses are predictive and as such, the tone is often in future tense.

From the available options, only option B sound predictive of what might happen in the future.

Hence, the correct option is B.

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