Which statement best explains why greenhouse gases contribute to Earth's warming?

• A. Greenhouse gases trap heat in the atmosphere, leading to warming.
• B. Volcanic eruptions can affect temperature.
• C. Oceans reflect all sunlight, cooling the planet.
• D. Earth's rotation speeds up leading to warming.

Answer: (A)

The main concept is the greenhouse effect: certain gases in the atmosphere trap heat, warming the surface. Sunlight reaches Earth and mostly passes through the atmosphere, warming the surface. That heat is then radiated back as infrared energy. Greenhouse gases—like water vapor, carbon dioxide, and methane—absorb much of that infrared radiation and re-radiate it in all directions, including back toward the ground. This trapping of heat reduces the amount escaping to space, so the surface and lower atmosphere warm.

That idea is exactly what the statement describes, so it’s the best explanation for why greenhouse gases contribute to Earth's warming. The other statements miss the key mechanism: volcanic eruptions can affect temperatures temporarily via aerosols, but they don’t explain the persistent warming caused by greenhouse gases; oceans don’t reflect all sunlight; and Earth’s rotation doesn’t drive warming in this context.