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.
Know your predicted grade
Take timed mock exams and get detailed feedback on every answer. See exactly where you're losing marks.
IB-style question — albedo and surface change [2]
As the climate warms, bright sea ice in the Arctic melts and is replaced by dark open ocean. Explain how this change affects the region's albedo and temperature. [2]
How to answer it, step by step
- Compare the surfaces
• Sea ice is light and reflective (high albedo, reflects most sunlight).
• Open ocean is dark (low albedo, absorbs most sunlight). - Link to temperature
• Replacing ice with ocean lowers the average albedo, so more sunlight is absorbed.
• The region warms further, melting more ice (a positive feedback).
Final answer
Define albedo as reflectivity and tie 'darker surface → lower albedo → more absorbed → warmer' clearly; naming the ice–albedo feedback earns full credit.
IB-style question — albedo calculation [2]
A field of fresh snow reflects 85 W m⁻² of an incoming 100 W m⁻². After it melts to bare dark soil, the same field reflects only 12 W m⁻². Calculate the albedo of each surface (as a percentage). [2]
How to answer it, step by step
- Write the albedo formula
• Albedo (%) = (reflected ÷ incoming) × 100.
• Incoming = 100 W m⁻² for both surfaces. - Substitute and solve each
• Snow = (85 ÷ 100) × 100 = 85%.
• Soil = (12 ÷ 100) × 100 = 12%.
Final answer
Show reflected ÷ incoming × 100 and give the % sign for both — high albedo (snow) vs low albedo (soil) explains why melting drives extra warming.