Which would most likely cause a reduction in the amount of coal and natural gas on Earth?

The option highlighting a continual increase in the number of people on Earth points to a significant factor affecting the demand for energy sources like coal and natural gas. As population grows, so does the need for energy to support the increased use of electricity, heating, and transportation. This heightened demand can lead to accelerated extraction and consumption of fossil fuels, resulting in a depletion of these resources over time.

In contrast, while pollution, water availability, and rainforest loss are critical environmental issues, they do not directly influence the reduction of coal and natural gas reserves. Pollution may impact how these resources are viewed and utilized, but it does not inherently lead to a decrease in their quantity. Similarly, a decrease in water in aquifers or rainforests relates more to water resource management and ecological health, rather than directly impacting the supply of fossil fuels. Thus, population growth effectively correlates with increased usage and subsequent reduction of these vital energy resources.