Final answer:
About 5 percent of carbon emissions remain in the atmosphere.
Step-by-step explanation:
The correct answer is A) 5 percent.
According to the given information, over 90% of the increase in carbon dioxide emissions has occurred over the past 100 years. While the concentration of carbon dioxide in the atmosphere is predicted to reach double the pre-industrial level by 2050, it is estimated that about 5% of carbon emissions remain in the atmosphere.