Key Idea: Most marks in topic 2.4 come from reading climate graphs and biome maps and explaining where biomes are. At HL, learn El Niño and tropical cyclones too.
1. Where biomes are (most marks)
- Temperature and precipitation decide which terrestrial biome forms.
- Insolation depends on latitude; altitude makes places colder.
- On a biome graph, find the rainfall and temperature, then read the biome.
- Name the limiting factor: too cold, too dry, or too little light.
2. Climate graphs and biomes
- Climate is the average over about 30 years; weather is the short term.
- Temperature range = warmest month minus coldest month, with units.
- Six groups: freshwater, marine, forest, grassland, desert, tundra.
- Learn two features of each: climate, plants, soil, productivity.
3. Oceans, El Niño, cyclones (HL)
- Currents carry heat from the tropics towards the poles: the Gulf Stream warms western Europe.
- In El Niño the Walker circulation weakens, so warm water spreads east across the Pacific.
- Tropical cyclones form over oceans warmer than about 26.5°C.
- Warmer oceans give cyclones more energy, so strong storms become more common.
How it is examined:
| Question | How to score |
|---|---|
| [1] Identify a biome or vegetation from a map | Match the colour to the key and copy the name in full. |
| [1] State a range or month from a climate graph | Read the bars and the line carefully; give units. |
| [2] Distinguish two climates from climate graphs | One point on temperature, one on rainfall, each with both places. |
| [4] Identify four features of a named biome | Climate, plants, soil and productivity: one feature each. |
| [4] Outline how the tricellular model explains biomes | Rising air, rain, rainforest; sinking air, dry, desert. |
Key terms, one line each:
| Term | In one line |
|---|---|
| Biome | a group of similar ecosystems that developed in similar climates |
| Tricellular model | three cells of air in each hemisphere that move heat and rain |
| Walker circulation | the east-to-west loop of air across the tropical Pacific |
| El Niño | a weaker or reversed Walker circulation: warm water spreads east |
| La Niña | a stronger Walker circulation: the east Pacific is cooler than usual |
| Tropical cyclone | a rapidly spinning storm with a low-pressure centre, formed over warm ocean |
Last-minute check: answer, then tap to see.
What happens to the Walker circulation in El Niño? It weakens or reverses.
How warm must the sea be for a tropical cyclone? About 26.5°C or more.
Why may a predicted biome not develop? Other factors: soil, fire, grazing or people.
How does El Niño affect Peru's fishing? Warm water stops upwelling, so fish catches collapse.
Why are strong cyclones becoming more common? Warmer oceans give storms more energy.
Peru's anchoveta catch fell from about 12.5 million tonnes in 1994 to 1.7 million tonnes in 1998, after the strong 1997-98 El Niño. Explain how El Niño caused this fall.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Exam tips
- On a map, match the colour to the key and copy the name exactly.
- On a climate graph, bars are rainfall and the line is temperature: check the axes.
- In a distinguish answer, use 'whereas' and give both places in each point.
- For El Niño, go step by step: winds, warm water, upwelling, food chain.