PHYSICS · Multi-part · IB Diploma Programme · Physics · The greenhouse effect · The greenhouse effect
Problem
Two planets, X and Y, orbit a Sun-like star at the same distance and have identical sizes and rotation rates. Planet X has an average visible-light reflectivity (albedo) of 0.75, whereas planet Y has an albedo of 0.25.
Answer the following about the role of surface reflectivity in determining planetary temperature.
(1) Describe qualitatively how a planet’s albedo influences the equilibrium temperature reached at its surface.
(2) Without performing any numerical calculation, identify which planet will attain the higher equilibrium surface temperature and provide a clear physical justification for your choice.
(3) Suppose both planets later develop extensive cloud cover that raises each albedo by an additional 0.10. Explain how this change would affect the equilibrium temperature of each planet and whether the temperature difference between the two planets would increase, decrease, or remain the same. Justify your answer using physical reasoning.