The correct answer is option C) greenhouse effect.

The Greenhouse Effect:

The greenhouse effect is a natural phenomenon that occurs when certain gases in the Earth's atmosphere trap heat from the sun and prevent it from escaping back into space. This process is essential for maintaining the Earth's temperature within a range that supports life. However, when the concentration of these greenhouse gases increases due to pollution, it becomes harmful.

Explanation:

1. Definition of the Greenhouse Effect:
- The greenhouse effect refers to the process by which certain gases, such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), trap heat in the Earth's atmosphere.
- These gases act like a blanket, allowing sunlight to enter the atmosphere but preventing some of the heat from escaping back into space.

2. Natural Greenhouse Effect:
- The natural greenhouse effect is crucial for maintaining the Earth's average temperature at around 15°C (59°F), which is necessary for supporting life.
- Without this natural effect, the Earth would be too cold to sustain life as we know it.

3. Human Activities and Pollution:
- Human activities, such as the burning of fossil fuels (coal, oil, and natural gas), deforestation, and industrial processes, have significantly increased the concentration of greenhouse gases in the atmosphere.
- These activities release large amounts of CO2 and other greenhouse gases, contributing to the enhanced greenhouse effect.

4. Harmful Effects of Enhanced Greenhouse Effect:
- The enhanced greenhouse effect, caused by human activities and pollution, leads to global warming.
- Global warming refers to the long-term increase in Earth's average temperature, which has numerous harmful consequences:
- Melting of polar ice caps and glaciers, leading to rising sea levels and coastal flooding.
- Changes in weather patterns, including more frequent and intense heatwaves, droughts, storms, and hurricanes.
- Disruption of ecosystems, impacting biodiversity and causing the extinction of various plant and animal species.
- Negative effects on agriculture, food production, and water resources, leading to food shortages and water scarcity in many regions.

Conclusion:

The greenhouse effect is a natural phenomenon that becomes harmful due to pollution. Human activities and the release of greenhouse gases have intensified the greenhouse effect, leading to global warming and its associated negative impacts on the environment and human society. It is crucial to reduce pollution and mitigate greenhouse gas emissions to minimize the harmful effects of the enhanced greenhouse effect.