Albedo explained
Big idea: Albedo is how reflective a surface is. Light surfaces reflect more energy; dark surfaces absorb more. This affects local and global temperatures.
High vs low albedo
High albedo (reflective)
- Fresh snow: 0.8–0.9 (80–90%)
- Thick clouds: 0.6–0.9
- Sea ice: 0.5–0.7
- Desert sand: 0.3–0.4
Low albedo (absorptive)
- Open ocean: 0.06 (6%)
- Dark soil: 0.1
- Forests: 0.1–0.2
- Asphalt: 0.04
The ice-albedo feedback loop
This is a positive feedback loop — a change that amplifies itself:
- Temperature rises → ice melts
- Ice (high albedo) is replaced by ocean (low albedo)
- More solar radiation is absorbed instead of reflected
- This causes more warming → more ice melts → and so on
Exam tip: The ice-albedo feedback is a favourite exam topic! Always explain it as a positive feedback loop where the effect amplifies the cause.
Global heat redistribution
Big idea: The tropics receive more solar energy than the poles, but heat is redistributed around the globe through atmospheric circulation and ocean currents.
Why is heat unevenly distributed?
- The equator receives more direct sunlight (concentrated energy)
- The poles receive sunlight at a low angle (spread over larger area)
- Without redistribution, the equator would be much hotter and poles much colder
Mechanisms of heat transfer
- Convection currents: Warm air rises at the equator, moves toward poles, cools and sinks — creates global circulation cells (Hadley, Ferrel, Polar)
- Ocean currents: Warm surface currents carry heat from equator to poles; cold deep currents return it
- Latent heat: Water evaporates at warm latitudes (absorbing heat), condenses at cooler latitudes (releasing heat)
Heat moves from where there's excess (equator) to where there's deficit (poles). This moderates global temperatures and drives weather patterns.
Exam tip: In questions about temperature regulation, include both atmospheric (convection) and oceanic (currents, latent heat) mechanisms.