Which statement best defines radiative forcing and climate sensitivity?

• A. Radiative forcing equals net upward energy flux at the top of the atmosphere; climate sensitivity describes future emission rates.
• B. Radiative forcing is a measure of surface albedo only; climate sensitivity is unrelated.
• C. Radiative forcing is the perturbation in the net downward energy flux at the top of the atmosphere caused by a driver, measured in W/m²; climate sensitivity describes how much the global mean temperature would eventually change for a given forcing, including feedbacks.
• D. Radiative forcing is the increase in solar output; climate sensitivity is the rate of greenhouse gas emission.

Answer: (C)

Radiative forcing is the perturbation in the net downward energy flux at the top of the atmosphere caused by a driver, measured in W/m². It acts as the initial push to Earth’s energy balance when something in the climate system changes, like more greenhouse gases or a change in solar output. Climate sensitivity describes how much the global mean temperature would eventually change for that forcing, once the system reaches a new equilibrium, and it includes feedbacks such as water vapor amplification, ice-albedo changes, and cloud responses. This pairing is what makes the statement correct: it clearly separates the immediate energy balance change from the eventual temperature response considering feedbacks. The other descriptions either misstate what forcing measures, oversimplify forcing to surface albedo, or confuse climate sensitivity with emission rates, or tie forcing only to solar output.