Answer:
Here are a few examples:
Volcanic eruptions.
Retreat of glaciers.
Flooding accompanied by severe soil erosion.
Landslides.
Nuclear explosions.
Oil spills.
Abandonment of a manmade structure, such as a paved parking lot.
Explanation:
Among the given choices, the only positive effect that may be thought off with the increase in level of CO2 in the atmosphere is the increase of plant growth. Carbon dioxide is an essential compound in the photosynthesis of plants. Therefore, the answer should be letter C.