Final answer:
Lower temperatures or less rain increase CO₂ levels, while higher temperatures or more rain decrease CO₂ levels, making option (b) Increases, Decreases the correct answer. CO₂'s role in the greenhouse effect is crucial for Earth's climate balance.
Step-by-step explanation:
The presence of CO₂ in Earth's atmosphere does function similarly to a thermostat, influencing the planet's climate. To address the fill-in-the-blank question:
Lower temperature or less rain increases CO₂. Higher temperature or more rain decreases CO₂.
The appropriate answer to the question is (b) Increases, Decreases. Lower temperatures and drier conditions can lead to higher CO₂ levels because there is less vegetation growth to absorb the CO₂. Conversely, higher temperatures and more rain can decrease CO₂ levels due to increased vegetation growth and therefore more CO₂ being removed from the atmosphere through the process of photosynthesis.
Carbon dioxide (CO₂) is a key greenhouse gas that, alongside others like methane and water vapor, traps heat in the atmosphere, contributing to the greenhouse effect and subsequently affecting global temperatures and weather patterns. This balance is essential for maintaining a climate that can support a wide variety of life on Earth.