Rising concentrations of greenhouse gases alter Earth's radiative equilibrium by...

• A. absorbing a greater amount of radiation from Earth's surface, thus making Earth warmer
• B. reflecting more solar radiation away from Earth
• C. increasing the albedo of the surface
• D. shielding Earth from cosmic radiation

Answer: (A)

Rising greenhouse gas levels change Earth's radiative balance by absorbing infrared radiation (heat) emitted from the surface and re-emitting it in all directions. This traps more heat in the lower atmosphere and at the surface, so less infrared escapes to space. The result is a positive radiative forcing that warms the planet until a new balance is reached.

This is why the best explanation is that more heat is absorbed from Earth's surface, making Earth warmer. Greenhouse gases don’t mainly reflect sunlight or increase surface albedo, and they don’t shield us from cosmic radiation; their primary effect is on infrared wavelengths emitted by the surface.