The correct answer is: A. An increase.
Albedo is the fraction of solar radiation that is reflected back to space by a surface. A higher albedo means that more sunlight is reflected back to space, and a lower albedo means that more sunlight is absorbed by the surface.
The radiative equilibrium temperature of a planet is the temperature at which the amount of energy absorbed by the planet from the Sun is equal to the amount of energy emitted by the planet back into space. If the albedo of a planet increases, then more sunlight is reflected back to space, and the planet will absorb less energy from the Sun. This will cause the planet to cool.
The opposite is also true. If the albedo of a planet decreases, then less sunlight is reflected back to space, and the planet will absorb more energy from the Sun. This will cause the planet to warm.
Therefore, an increase in albedo would be accompanied by an increase in radiative equilibrium temperature.
Here is a brief explanation of each option:
- Option A: An increase in albedo would be accompanied by an increase in radiative equilibrium temperature. This is because a higher albedo means that more sunlight is reflected back to space, and a lower albedo means that more sunlight is absorbed by the surface. The radiative equilibrium temperature of a planet is the temperature at which the amount of energy absorbed by the planet from the Sun is equal to the amount of energy emitted by the planet back into space. If the albedo of a planet increases, then more sunlight is reflected back to space, and the planet will absorb less energy from the Sun. This will cause the planet to cool. The opposite is also true. If the albedo of a planet decreases, then less sunlight is reflected back to space, and the planet will absorb more energy from the Sun. This will cause the planet to warm.
- Option B: A decrease in albedo would be accompanied by a decrease in radiative equilibrium temperature. This is the opposite of what is actually observed.
- Option C: No change in albedo would be accompanied by no change in radiative equilibrium temperature. This is also not what is actually observed.
- Option D: Unstable oscillations in albedo would be accompanied by unstable oscillations in radiative equilibrium temperature. This is not a realistic scenario.