Water and climate regulation
Big idea: Water is Earth's thermostat. It absorbs, stores, and redistributes heat around the planet, keeping temperatures stable enough for life.
How water regulates temperature
- High specific heat capacity — water absorbs large amounts of heat with only a small temperature change (oceans act as heat sinks)
- Latent heat — evaporation absorbs heat (cooling), condensation releases heat (warming)
- Ocean currents — redistribute heat from the equator to the poles (e.g., the Gulf Stream warms western Europe)
- Water vapour as a greenhouse gas — traps heat in the atmosphere (can act as a positive feedback during warming)
- Albedo — ice/snow reflect sunlight (cooling), open water absorbs sunlight (warming)
For outline-style answers, give several distinct points (one per sentence), such as: high specific heat capacity, latent heat transfer, ocean currents, water vapour as a greenhouse gas, and albedo effects from ice/snow.
Water and the carbon cycle connection
Oceans also regulate climate by acting as carbon sinks. They absorb about 25% of human CO2 emissions, but this contributes to ocean acidification (see 4.4).
Water regulates climate through: (1) absorbing heat, (2) transporting heat via currents, (3) transferring heat via evaporation/condensation, (4) reflecting sunlight when frozen, and (5) absorbing CO2.
IB-style question — missing stores and inputs [1]
A simple water-cycle diagram shows only trees, surface run-off and evapotranspiration. Name one freshwater storage that is missing from this diagram. [1]
How to answer it, step by step
- **Think where fresh water sits on land**<br>• Liquid stores: lakes, rivers, reservoirs, groundwater/aquifers.<br>• Frozen store: glaciers and ice.
- **Pick one not already drawn**<br>• The diagram only shows trees + run-off, so any of the above counts.<br>• Example answer: groundwater (aquifer).
Final answer
Name an actual store of water (a lake, glacier, aquifer…), not a flow or process like ‘rain’ or ‘evaporation’.
IB-style question — infiltration difference [1]
Of 100 mm of rainfall, a forest lets 55 mm infiltrate the soil while a nearby car park lets only 12 mm infiltrate. Calculate the difference in infiltration between the two sites. [1]
How to answer it, step by step
- **Write the subtraction**<br>• Difference = forest infiltration − car-park infiltration.<br>• = 55 mm − 12 mm.
- **Work it out and add the unit**<br>• 55 − 12 = 43.<br>• Difference = 43 mm.
Final answer
Always show the subtraction and include the unit (mm or %) — a bare number loses the mark.