The major cause of the greenhouse effect is carbon dioxide in the atmosphere.
The major cause of the greenhouse effect is carbon dioxide in the atmosphere. To arrive at this answer, we can eliminate the options that mention carbon dioxide in the water, as the greenhouse effect primarily occurs in the Earth's atmosphere. Similarly, soot from coal plants in the water is not a major cause of the greenhouse effect, as it is the presence of greenhouse gases like carbon dioxide that trap heat in the atmosphere. Therefore, the correct answer is soot from coal plants in the atmosphere.
