What is the primary function of the greenhouse effect for Earth's climate?

• A. It warms the planet to make it habitable
• B. It cools the planet by reflecting sun
• C. It has no impact on temperature
• D. It causes extreme weather events only

Answer: (A)

The main function of the greenhouse effect is to keep Earth’s surface warm enough for life by trapping heat in the lower atmosphere. When sunlight reaches Earth, it heats the surface, which then emits infrared radiation. Greenhouse gases—like water vapor, carbon dioxide, and methane—absorb much of that infrared energy and re-radiate it in all directions, including back toward the surface. That trapping acts like a blanket, raising the average surface temperature compared with a planet without those gases. Without this natural warming, Earth would be far colder—roughly on the order of 33°C cooler on average—making it much less hospitable for living things.

Saying it cools the planet by reflecting sunlight, or that it has no impact on temperature, or that it only causes extreme weather misses the essential mechanism: heat retention rather than reflection. The greenhouse effect sets the baseline climate by moderating temperatures, though human changes to greenhouse gas concentrations can amplify this warming and influence weather patterns.