In the Earth's energy budget, what is the balance?

• A. The amount of solar radiation energy coming in is greater than the infrared radiation emitted.
• B. The amount of solar radiation energy coming in is equal to the infrared thermal radiation emitted back to space.
• C. The energy budget is unrelated to radiation.
• D. All solar energy is reflected back without absorption.

Answer: (B)

The energy budget is about balancing the energy Earth receives with the energy it emits. On average, the amount of solar radiation that Earth absorbs is equal to the infrared radiation it emits back to space. This balance keeps the global climate relatively stable over time. Some solar energy is reflected back before it’s absorbed, but the portion that is absorbed must eventually be radiated away as heat in the infrared. The greenhouse effect doesn’t remove the need for this balance; it traps some heat and warms the surface, but the net energy leaving Earth to space still matches the energy coming in. If more energy came in than left, the planet would warm until balance is restored, and if more left than came in, it would cool until balance is restored.