Questions: Planetary Albedo and Temperature Feedback Processes

Question 1

Venus has a much higher albedo (~0.77) than Earth (~0.30) and absorbs less solar radiation per unit area, yet its surface temperature is far higher than Earth's. The best explanation is:

• A. High albedo traps outgoing infrared radiation, raising surface temperature
• B. The greenhouse effect retains the energy that is absorbed so efficiently that even a lower absorbed flux produces extreme surface warming
• C. Venus's proximity to the Sun still delivers more total solar flux despite the higher albedo
• D. The ice-albedo feedback on Venus continuously amplifies absorbed solar energy

Answer: (B)

Venus's extreme surface temperature (~465°C) despite high albedo is the definitive illustration that albedo and surface temperature are not directly linked — the greenhouse effect operates independently on the absorbed fraction. Venus's dense CO₂ atmosphere creates an almost-opaque greenhouse, so the ~23% of solar energy that does get absorbed cannot escape as infrared. This is why we must track both the reflection side (albedo) and the absorption/emission side (greenhouse) to predict surface temperature.

Question 2

Arctic sea ice begins melting due to a slight initial warming. The ice-albedo feedback then:

• A. Counteracts the warming by increasing water vapor, which reflects more sunlight
• B. Has no net effect because darker oceans emit more infrared radiation, balancing the extra absorption
• C. Amplifies the warming: darker ocean surface absorbs more sunlight, driving further warming and more ice loss
• D. Acts as a negative feedback by increasing evaporation, which cools the surface

Answer: (C)

Ice-albedo feedback is a positive feedback — it amplifies the initial perturbation rather than restoring equilibrium. Melting ice exposes darker ocean or land (lower albedo), which absorbs more of the incoming solar radiation, raising temperature, which melts more ice, and so on. The same logic runs in reverse for cooling: expanding ice raises albedo, reflects more sunlight, cools further, and grows more ice. The word 'positive' means amplifying, not stabilizing or beneficial.

Question 3

A positive climate feedback amplifies an initial temperature perturbation in both the warming and cooling directions.

• T. True
• F. False

Answer: True

A positive feedback means the system's response reinforces the initial change, regardless of direction. Ice-albedo feedback amplifies warming (less ice → lower albedo → more absorption → more warming) and amplifies cooling (more ice → higher albedo → less absorption → more cooling). This bidirectionality is why positive feedbacks can drive Earth into both ice ages (runaway cooling) and hothouse states (runaway warming).

Question 4

An increase in a planet's average albedo typically leads to a lower equilibrium surface temperature.

• T. True
• F. False

Answer: False

Albedo controls only the reflected fraction of solar radiation — it is just one side of the energy balance. Surface temperature also depends on the greenhouse effect, which operates on the absorbed fraction. Venus demonstrates this: despite albedo ~0.77 (vs. Earth's ~0.30), Venus has a much higher surface temperature because its dense CO₂ atmosphere traps outgoing infrared with near-perfect efficiency. A planet can have high albedo and still be very hot if its greenhouse effect is strong enough.

Question 5

Why is the ice-albedo feedback classified as a positive feedback, and what prevents it from inevitably driving Earth to either complete glaciation or complete ice-free conditions?

Model answer: Ice-albedo is positive because it amplifies perturbations: warming reduces ice cover, lowering albedo, increasing solar absorption, causing more warming. Cooling grows ice, raises albedo, reduces absorption, causing more cooling. It is prevented from running away by competing negative feedbacks operating on longer timescales — principally the carbonate-silicate weathering cycle, where higher CO₂ increases chemical weathering, drawing CO₂ out of the atmosphere and cooling the planet back toward equilibrium over millions of years.

The key distinction between positive and negative feedbacks is crucial: positive feedbacks amplify, negative feedbacks stabilize. Earth's climate is metastable because multiple feedbacks operate on different timescales — ice-albedo amplifies on short timescales, while geochemical cycles like the carbonate-silicate system provide long-timescale stabilization. Planets that lack such long-timescale negative feedbacks (like early Venus) can experience runaway positive feedbacks with no recovery.