Climate and natural vegetation

Cambridge IGCSE Geography 0460 · Paper 1 Geographical Themes, Theme 2 The natural environment Syllabus: 2025 and 2026 Official syllabus point: 2.5

Read this before anything else. This topic is examined up to and including the November 2026 series, and no further. If you are sitting 0460 in 2027 or later, close this page. The 2027 syllabus replaces this material with a new Topic 3 Changing ecosystems, which keeps the tropical rainforest but pairs it with Antarctica and deletes hot deserts completely, and with a new Topic 5 Climate change, which is not in this syllabus at all. Revising 2.5 for a 2027 paper means learning a hot desert climate, hot desert vegetation and hot desert wildlife that your paper cannot ask you about. Use the 2027 notes instead.

If your exam is June 2026 or November 2026, this is your topic and everything below applies to you.

1. What 2.5 asks, and how it is examined

The syllabus states three things candidates should be able to do. These are the exact content statements, and nothing outside them can be set:

Describe and explain the characteristics of two climates: equatorial, hot desert.

Describe and explain the characteristics of tropical rainforest and hot desert ecosystems.

Describe the causes and effects of deforestation of tropical rainforest.

The further guidance column then fixes the scope precisely:

• Climate characteristics including temperature (mean temperature of the hottest month, mean temperature of the coolest month, annual range) and precipitation including convection and relief rainfall (the amount and seasonal distribution).
• Factors influencing the characteristics of these climates including latitude, pressure systems, winds, distance from the sea, altitude and ocean currents.
• Climatic graphs showing the main characteristics of temperature and rainfall of the two climates.
• The relationship in each ecosystem of natural vegetation, soil, wildlife and climate.
• Effects on the natural environment (both locally and globally) and effects on people.

Two case studies are required: an area of tropical rainforest and an area of hot desert.

The single most important scope point. The syllabus asks for the causes and effects of deforestation. It does not ask you to manage it, evaluate strategies, or write about sustainability. Sixteen 7 mark questions on this topic were set between 2020 and 2024 and not one of them asked for management. Management of environmental damage lives in a different topic, 3.7 Environmental risks of economic development, which is where sustainable development, resource conservation and desertification are assessed. Do not waste a 2.5 answer on the Amazon Fund.

Where the marks sit. On Paper 1 this topic appears as one whole 25 mark question, usually numbered 3 or 4, built the same way every time: (a)(i) 1 mark, (a)(ii) 2 marks, (a)(iii) 3 marks, (a)(iv) 4 marks, (b)(i) 3 marks, (b)(ii) 5 marks, then (c) worth 7 marks with a levels mark scheme. On Paper 2 the topic appears almost every session as a climate graph question plus a vegetation photograph, typically Question 4 or Question 5. Paper 2 questions need no case study knowledge, but they need real accuracy in reading a graph.

2. Where the two climates and ecosystems are found

Distribution questions are worth 2 or 3 marks and are asked constantly. The mark schemes want a pattern plus latitude figures plus named continents. A list of continents alone will not reach full marks, and neither will "near the Equator" on its own.

Tropical rainforest and equatorial climate

For Africa specifically, one mark scheme credited "10°N to 3°S", West and Central Africa, plus a small area on or near the Tropic of Capricorn and in Madagascar. That level of precision is what separates 2 marks from 1.

Hot deserts

Named deserts the exam has used: Sahara (Africa), Kalahari and Namib (southern Africa), Arabian and Thar (Asia), Simpson and Great Victoria (Australia), Mojave, Sonoran and Chihuahuan (North America), Atacama (South America).

Exam trap: "mostly on the west sides of continents" is a tick box answer on Paper 2 and a mark on Paper 1. Students almost never say it, because it looks like an odd thing to notice. It is caused by cold ocean currents running up the western coasts in the tropics.

3. Reading climate graphs

The syllabus requires "climatic graphs showing the main characteristics of temperature and rainfall of the two climates", and Paper 2 tests it with real precision. Every one of these is a mark that is lost by carelessness rather than by ignorance.

Terms you must be able to calculate

Read the axes before you read the graph. Temperature is a line on the left axis. Rainfall is a set of bars on the right axis. Paper 2 asks for "the average monthly rainfall in June" and students give the temperature.

Show the calculation. A 2 mark range question awards one mark for the working and one for the answer. A real mark scheme reads: "Calculation 28 °C to 27 °C (1 mark). Answer 1 °C (1 mark)". Writing only "1 °C" scores 1 out of 2.

Southern hemisphere check. If the hottest months are December, January and February, the place is in the southern hemisphere. Paper 2 has asked exactly this about a hot desert graph, and it is a free mark.

Identifying which graph is which. A mark scheme for "identify the graph which shows a hot desert climate, give two reasons" carried the warning: do not credit reasons if the wrong graph is selected. Pick the graph first, carefully, then justify. It also refused credit for simply listing statistics for each month; the reasons had to be climate characteristics such as low rainfall, high temperatures and seasonal variation in temperature.

4. The equatorial climate

The equatorial climate is hot all year, wet all year, and almost seasonless.

The figures to learn

These are drawn straight from Cambridge mark schemes for equatorial climate graphs, so they are the numbers the examiner has in mind:

The nuance that earns the top marks on rainfall. Cambridge set a 4 mark question asking whether "little seasonal variation" is true for both temperature and rainfall, and the mark scheme answer was: true for temperature but not true for rainfall. On that graph monthly totals ran from 114 mm to 396 mm, a difference of 282 mm, with a drier spell from June to November. Learn this. Equatorial temperature barely moves; equatorial rainfall varies noticeably from month to month even though no month is dry.

The daily weather pattern

Cambridge has asked candidates to put this sequence in order, and it is worth learning as a sequence:

1. sun rises in a clear sky
2. intense heating and evaporation through the morning
3. cumulus clouds form by late morning
4. the sky becomes covered by cloud in the early afternoon
5. heavy convectional rain and thunder in the afternoon
6. by sunset the sky is clear again.

This repeats almost every day, which is exactly why there are no seasons.

Explaining the characteristics

Why temperatures are high all year:

1. low latitude, on or near the Equator
2. the sun is almost overhead all year
3. the rays strike at a high angle and are concentrated on a small area
4. insolation is at its maximum
5. high temperatures every month.

Why there is little seasonal variation: the angle of the sun and the length of day barely change through the year at the Equator, so nothing drives a seasonal swing.

Why rainfall is so high:

1. intense heating of land, forest and rivers
2. very high evaporation and transpiration
3. warm, moist air rises in convection currents
4. low pressure at the surface
5. air cools as it rises
6. condensation forms cumulonimbus clouds
7. the clouds reach saturation
8. heavy convectional rain falls in the afternoon.

Marks note: on the 4 mark version of this question the mark scheme awards a mark per correct process, in order: heating, evaporation, transpiration (or evapotranspiration for one mark instead of both), rising air or convection, cooling, condensation, saturation. It then adds: maximum 2 marks if the answer is in the wrong context, for example relief rainfall. Equatorial rainfall is convectional. Do not describe air rising over mountains.

Why humidity is always high: high temperatures all year, high rainfall all year, warm air holds more moisture, and evaporation rates are very high.

5. The hot desert climate

The hot desert climate is very dry, very hot by day, and marked by large temperature ranges.

The figures to learn

A Cambridge worked example. The Simpson Desert in Australia was set as a climate graph. In January its mean daily maximum was 36 °C and its mean daily minimum 21 °C, giving a range of 15 °C, and its average December rainfall was 7 mm. Australian deserts lie south of the Equator, so January is midsummer there.

A second Cambridge worked example. Two Saharan stations were compared. In Salah, deep inland in Algeria, had a mean May temperature of 30 °C and a mean annual temperature range of 23.5 °C. Nouakchott in Mauritania, on the Atlantic coast, was more moderate: cooler in summer, warmer in winter, wetter, with a small amount of rain in August and September. The mark scheme's explanation was simply "one is coastal and one is inland". Distance from the sea is doing all the work.

Explaining the characteristics

Why rainfall is low. There are six separate reasons, and the 4 mark questions expect you to develop two or more rather than list all six. This is the single most repeated question in the topic:

1. hot desert sits under high pressure
2. air descends and is warmed by compression
3. relative humidity falls
4. condensation cannot occur
5. no clouds form
6. annual rainfall stays below 250 mm.

Marks note: the mark scheme for a 4 mark version of this question rejected "distance from the sea" written as a bare list item with no explanation, gave only 1 mark for "dry winds" alone, and called "too hot for water to condense" too vague. Every factor needs its mechanism.

Why the diurnal range is so large:

1. clear skies and no cloud
2. the sun's rays are not blocked and reach the surface directly by day
3. the ground heats rapidly to very high temperatures
4. at night there is no cloud blanket to trap outgoing radiation
5. heat escapes rapidly to space
6. night temperatures fall steeply, sometimes close to 0 °C.

Add that sand and rock have a low heat capacity, so they both heat and cool quickly, and that low humidity means there is little water vapour in the air to hold heat.

Why the annual range is also large: unlike the Equator, the tropics do get a real change in the angle of the overhead sun through the year, so summer insolation is much higher than winter insolation. A mark scheme accepted "changing angle of overhead sun during the year" and "variation in amount of insolation" for this.

6. The six factors that control both climates

The syllabus names six factors "including latitude, pressure systems, winds, distance from the sea, altitude and ocean currents". Any of them can be asked about directly, so hold each one as a mechanism rather than a label.

Exam trap: the Atacama question asked specifically about the cold ocean current and the prevailing winds, and awarded 2 marks for each. When a question splits itself like that, split your answer under the same two headings, or you will write four marks' worth about one factor and score two.

7. Convectional and relief rainfall

The syllabus names both types by name. Convection is the one that matters for the equatorial climate, and relief matters for the rain shadow explanation in deserts.

Convectional rainfall

1. the sun heats the ground strongly
2. the air in contact with the ground is warmed
3. water evaporates from surfaces and transpires from plants
4. the warm, moist air becomes less dense and rises
5. it expands and cools as it rises
6. it reaches dew point and water vapour condenses on condensation nuclei
7. cumulus builds into towering cumulonimbus
8. the cloud reaches saturation and can hold no more
9. heavy rain, often with thunder and lightning, falls in the afternoon.

Convectional rain is typically intense, short lived, localised and daily in equatorial areas.

Relief (orographic) rainfall

1. moist air from the sea is forced to rise over a mountain barrier
2. it cools as it rises
3. condensation occurs and cloud forms
4. heavy rain falls on the windward slope
5. the air descends the far side, is compressed and warmed
6. its capacity to hold moisture rises
7. no condensation occurs
8. the leeward side lies in a dry rain shadow.

This is the mechanism behind the Atacama sitting behind the Andes, and behind many desert margins worldwide.

Marks note: describing relief rainfall in an equatorial rainfall question is explicitly capped at 2 marks by the mark scheme. Match the process to the climate.

8. What an ecosystem is

An ecosystem is a community of living things (plants, animals and micro organisms) together with the non living parts of their environment (climate, soil, water and rock), and all the links between them.

The syllabus wants "the relationship in each ecosystem of natural vegetation, soil, wildlife and climate". Four elements, and the relationships between them, not four separate lists.

The links run in every direction, and that is what a "describe three ways in which vegetation, soil and wildlife depend on each other" question is testing. Cambridge's own credited answers were: wildlife eats plants, birds and snakes eat smaller creatures, nutrients from dead animals and droppings return to the soil, the soil enables plants to grow, and populations are kept in balance.

Vocabulary that earns credit

• Producer: a plant, which makes its own food by photosynthesis.
• Consumer: an animal. Primary consumers eat plants (herbivores), secondary and tertiary consumers eat other animals (carnivores).
• Decomposer: fungi, bacteria and termites, which break down dead material and release nutrients back to the soil.
• Food chain: a single line of who eats whom. Food web: the many interlinked chains in a real ecosystem.
• Biodiversity: the number and variety of species present.

Food web questions. Paper 2 has set a rainforest food web and asked what happens if one species declines. The reasoning the mark scheme wanted, for a fall in orchids, was: fewer spider monkeys because their food supply falls, therefore less food for ocelots and jaguars, therefore fewer secondary and tertiary consumers. Follow the arrows upward through the web and name the species at each step. Vague answers about "damaging the ecosystem" are marked as too vague.

9. The tropical rainforest ecosystem

Climate inputs

Hot (about 27 °C every month), wet (over 2000 mm a year), humid, and with no dry season. Nothing ever stops growth, so growth is continuous, competition is ferocious, and biodiversity is enormous.

Structure: the four layers

This is a labelling question waiting to happen, and Cambridge has set it repeatedly with a cross section diagram.

Cambridge's own figures from set diagrams: emergents at 45 to 50 m against a canopy at 25 to 35 m; and on another paper an emergent maximum of 56 m with the canopy running from 30 m to 40 m.

Adaptations of the vegetation

The 5 mark and 7 mark questions want the feature plus the reason. A feature on its own is one mark; the pair is what builds a Level 3 answer.

Marks note: a mark scheme for the buttress and drip tip question awarded 2 marks for each and gave zero for "wide leaves for maximum sunlight" as an explanation of drip tips. Answer the feature you were asked about.

Wildlife and biodiversity

Rainforest biodiversity is the highest of any land ecosystem. The reasons Cambridge credits are: high rainfall and humidity all year, high temperatures and strong sunlight, conditions that do not change with the seasons so growth never stops, abundant food and rapid decomposition, many different habitats at different heights, and large undisturbed areas.

Adaptations of rainforest animals

• Living in the canopy, where the food is: prehensile tails, gripping hands and feet, and in some species gliding membranes.
• Camouflage against a background of green and dappled shade.
• Bright warning colours in poisonous species such as poison dart frogs.
• Strong beaks and jaws for hard fruit and nuts.
• Nocturnal habits to avoid daytime predators.
• Specialised diets, so many species can share the same forest without competing directly.

Named Amazon species worth carrying: jaguar, harpy eagle, howler and spider monkey, tapir, caiman, sloth, macaw, poison dart frog, piranha.

Soil and the nutrient cycle

Rainforest soils are latosols (also called oxisols or ferralsols): deep, red, rich in iron and aluminium, and surprisingly infertile.

The apparent contradiction is the whole point of this section, and Cambridge has set it as a systems diagram question:

• The largest nutrient store is the vegetation (biomass), not the soil. Cambridge's own mark scheme states this outright.
• Nutrients enter the system from rainfall and from weathered rock.
• Nutrients leave the system through leaching by heavy rain, through surface runoff, and when the biomass is removed.
• The cycle is fast and closed: leaves fall, the hot wet conditions let fungi, bacteria and termites decompose them within weeks, and the released nutrients are taken up again almost immediately by the shallow roots before rain can wash them away.

1. leaf litter falls
2. hot, humid conditions drive rapid decomposition
3. nutrients are released into a thin surface layer of soil
4. shallow, wide roots absorb them almost immediately
5. nutrients return to the biomass
6. the soil itself stays poor.

Why this matters for deforestation. Remove the trees and you remove the store. Heavy rain then falls directly on bare soil, leaching washes the thin nutrient layer down beyond root depth, and the soil is exhausted within two or three harvests. This is exactly why shifting cultivators moved on, and why cleared rainforest land is abandoned so quickly.

10. The hot desert ecosystem

Climate inputs

Under 250 mm of rain a year, arriving unpredictably. Very high daytime temperatures, cold nights, intense sunlight, low humidity, and strong drying winds. Water is the limiting factor in everything that follows.

The soil

• Thin, sandy or stony, and poorly developed.
• Very low organic matter, because there is little vegetation to supply leaf litter and decomposition is slow without moisture.
• Alkaline and often saline. Water is drawn up through the soil by capillary action, evaporates at the surface, and leaves its dissolved salts behind as a crust.
• Little leaching, because there is little water moving downward.
• Easily eroded by wind once any binding vegetation is disturbed.

Desert landforms worth naming: ergs (sand seas of dunes), regs (stony plains), hamadas (bare rock plateaux), wadis (dry valleys that flash flood), oases, and salt pans.

Vegetation adaptations

Desert plants are xerophytes: plants adapted to survive with very little water. The vegetation is sparse, low growing and widely spaced. The mark schemes for this are unusually detailed, and each of these pairings is worth marks.

Marks note: the 5 mark version of this question carries the instruction "explanation cannot be credited alone" and "do not credit examples alone, for example cacti; it needs cacti have long roots for credit". Naming plants is worth nothing by itself. Name the feature, then say what it does.

Wildlife adaptations

Cambridge has set this as a 5 mark question, and the credited answers were specific and physiological:

• Can survive long periods without water or food, and can store water or fat (the camel's hump stores fat, not water).
• Obtain water from succulent plants or from their food rather than by drinking.
• Large feet to spread weight and stop sinking into sand.
• Large ears with many blood vessels, which radiate excess heat away. The fennec fox is the classic example.
• Nocturnal habits, active at night and sheltering by day.
• Burrowing into sand or soil during the hottest hours, where it is far cooler.
• Concentrated urine and dry droppings, because their kidneys reclaim water, so very little is excreted.
• Thick outer coverings or scales that reduce moisture loss.
• Urinating on their own legs so that evaporation cools the blood, which then circulates back through the body.
• Light coloured coats that reflect heat.

Named Saharan species worth carrying: dromedary camel, fennec fox, addax antelope, dorcas gazelle, jerboa, horned viper, scorpion, desert monitor lizard.

The relationships between the four elements

1. low rainfall and intense heat
2. only xerophytic plants survive, and only sparsely
3. little leaf litter reaches the ground
4. soil organic matter and fertility stay very low
5. the sparse vegetation supports only a small number of specialised animals
6. animals in turn depend on plants for both food and water
7. so the whole ecosystem holds low biomass and low biodiversity, and is very slow to recover once damaged.

11. Deforestation: the causes

The syllabus asks for causes and effects, and the 5 mark and 7 mark questions on causes come round constantly. Sort them into groups, because a list of ten in one sentence rarely gets beyond Level 1.

Agriculture, the largest cause

• Cattle ranching, above all in the Amazon. Cambridge's own mark scheme identified cattle ranching as the main cause in South America.
• Commercial and cash crop plantations: oil palm in Indonesia and Malaysia, soy beans in Brazil, rubber, coffee and cocoa. Cambridge identified large scale agriculture as the main cause in Asia.
• Subsistence and smallholder farming, including slash and burn. Cambridge identified smallholder farming as the main cause in Africa.
• Pulpwood plantations for paper.

Real figures Cambridge has printed. A comparison of Africa and South America gave: commercial agriculture 66 per cent of deforestation in South America against 35 per cent in Africa, subsistence agriculture 18 per cent in South America against 40 per cent in Africa, and agriculture overall 84 per cent in South America against 75 per cent in Africa. The single sentence that scored best was: the main cause is commercial farming in South America but subsistence farming in Africa.

Extraction of resources

• Logging for hardwood timber such as mahogany and teak, for furniture, building materials, paper and export earnings.
• Fuelwood and charcoal collection.
• Mining and quarrying: gold, iron ore, bauxite, and drilling for oil.

Infrastructure and settlement

• Road and railway building, both to reach resources and to move timber. Roads are the multiplier: they open previously inaccessible forest to everyone else.
• Hydroelectric dams and reservoirs, which drown large areas of forest.
• Settlement growth, resettlement schemes, urban expansion and factory building.

The underlying reasons

These are the developed points that lift an answer into Level 2 and 3, because they explain why rather than listing what:

• The country needs economic development and foreign currency, and may be servicing debt.
• Individuals are poor and the forest is the resource they have.
• The forest area is vast and remote, so laws are almost impossible to enforce.
• Weak legislation and corruption mean permits are ignored or bought.
• Profit is put before the environment.

Explaining the distribution of deforestation

Cambridge set a map of Amazon deforestation in 2021 and asked why the pattern looked as it did. The credited reasoning:

• Clearance follows roads and railways, because access controls everything.
• Areas closer to towns, ports and dense population go first.
• Conservation areas and indigenous reserves stay forested.
• Different governments have different attitudes and different enforcement.
• Some areas have already been cleared, so nothing of value remains.
• Some areas have better quality or more valuable timber.

12. Deforestation: the effects

The syllabus asks for "effects on the natural environment (both locally and globally) and effects on people". Cambridge splits these three ways in the questions, and the mark schemes police the split strictly.

Local effects on the natural environment

• Loss of habitat and shelter for forest species.
• Death and forced migration of animals, and extinction of species with small ranges.
• Loss of biodiversity.
• Disruption of food chains and food webs: removing one species removes the food supply of everything above it.
• Soil erosion, because there are no roots to bind the soil, no canopy to intercept rain, and bare soil is exposed to rain splash and wind.
• Leaching and the rapid loss of the thin nutrient layer, so the soil becomes infertile within a few years.
• Soil compaction by machinery and cattle.
• Increased overland flow, because interception and infiltration both collapse.
• Flooding and flash floods in rivers downstream, and landslides on steep slopes.
• Siltation of rivers as eroded soil is washed in, and river pollution.
• Air pollution and smoke from burning.
• Locally hotter and drier conditions, because transpiration from the forest no longer feeds local rainfall.

Global effects on the natural environment

• Trees are a carbon sink. Fewer trees means less carbon dioxide absorbed by photosynthesis.
• Burning the cleared timber releases stored carbon dioxide straight into the atmosphere.
• Carbon dioxide builds up and forms a layer in the atmosphere.
• The sun's short wave rays pass through this layer, strike the Earth and are re radiated as long wave heat, which the layer traps. This is the enhanced greenhouse effect.
• Global temperatures rise, which is global warming.
• Ice caps and glaciers melt, and sea levels rise.
• Coastal lowlands flood, and mangroves are lost.
• Rainfall patterns change, bringing drought to some regions and heavier rain to others.
• Species elsewhere are lost as their habitats change, for example polar species as sea ice retreats.

Marks note, and this one is strict. The mark scheme for "how deforestation is threatening the local natural environment" prints a list of things not to credit: temperature increase, rainfall decrease, decreased evaporation and transpiration, and melting ice. Those are global effects. The reverse also applies: a global effects question refuses local answers unless they are clearly happening somewhere other than where the deforestation is. Read the word local or global and answer only that one.

Effects on people

Local people, mainly indigenous groups:

• Loss of land, homes and hunting grounds, and forced migration.
• Loss of culture, language and traditional way of life.
• Loss of resources: food, building materials, and plants used as medicines.
• Conflict with loggers, ranchers and plantation owners, sometimes fatal.
• Disease introduced by outsiders, such as influenza, to which forest peoples have no resistance.

Cambridge illustrated this with the Awa Guaja people of the Brazilian Amazon, and the credited reasons for their threatened extinction were: illegal logging and invasion of their territory, habitat destruction by loggers and ranchers, diseases to which they have no resistance, hunger from lost food supplies, and killings in conflict with loggers.

People elsewhere in the world:

• Flooding of coastal areas as sea levels rise, threatening low lying countries.
• Drought and failing harvests where rainfall patterns shift.
• Knock on effects such as less snow in mountain skiing regions and not enough water for irrigation.
• Loss of potential medicines from plants never yet studied.

And, honestly, positives, which mark schemes do credit:

• Jobs in logging, ranching, mining and processing.
• Economic development and export earnings for the country.
• Land for farming for people who have none.

Marks note on scale. One mark scheme for a global impacts question set the bar as: maximum 5 with no named places, maximum 6 with one named place, 7 marks needs two or more. On a question that says "you should refer to named places", one place is not enough.

13. Detailed case studies

The syllabus requires two: an area of tropical rainforest and an area of hot desert. Each must cover the ecosystem's climate, natural vegetation, soil and wildlife, and for the rainforest also the causes and effects of deforestation. Learn names, species and figures, because the 7 mark mark schemes describe Level 3 as needing "locational details, named places, statistics".

Scale warning. A mark scheme elsewhere in this syllabus states that a country name is not acceptable when the question asks for a named area. "Brazil" is a country. "Amazonia", "the Amazon basin", "the state of Pará" and "the forest around Manaus" are areas. Name at the scale the question asks for.

13a. Tropical rainforest: the Amazon, Brazil

Location and scale. The Amazon rainforest covers roughly 5.5 million km² of the Amazon river basin in South America, spread over nine countries, with around 60 per cent of it in Brazil. It also reaches into Peru, Colombia, Bolivia, Ecuador, Venezuela, Guyana, Suriname and French Guiana.

Climate, using Manaus. Manaus sits in the middle of the Brazilian Amazon at about 3 degrees south, and Cambridge has used it as a set climate graph more than once. From those mark schemes: mean monthly temperature is about 27 to 28 °C all year, giving an annual range of only 1 °C; March runs at about 26.5 to 27 °C and November at 28 °C; monthly rainfall runs from about 120 mm in June to about 250 mm in May; and the annual total is well over 2000 mm. The rain is convectional and falls almost every afternoon.

Vegetation. Four layers, with emergents such as the kapok and the Brazil nut tree rising above a continuous canopy. Buttress roots, drip tip leaves, lianas and canopy epiphytes including orchids and bromeliads. Everything is evergreen; growth never stops.

Soil. Deep red latosols, heavily leached, iron and aluminium rich, and infertile below a very thin surface layer of nutrients. The nutrient store is the biomass, not the soil.

Wildlife. Jaguar, harpy eagle, howler and spider monkeys, tapir, sloth, macaw, caiman, poison dart frogs, piranha, and enormous numbers of insect species. The forest is estimated to hold around a tenth of all known species on Earth.

People. Several hundred indigenous groups, including the Yanomami and the Awa Guaja of Maranhão, who are among the most threatened peoples in the world.

Causes of deforestation here

• Cattle ranching, the single largest cause in Brazil.
• Soy bean cultivation, much of it grown for animal feed and export.
• Logging, both legal and illegal, for hardwoods including mahogany.
• Mining, including the Carajás iron ore complex in the state of Pará, one of the largest iron ore operations in the world, and widespread illegal gold mining along the rivers.
• Roads, above all the Trans Amazonian Highway (BR 230), begun in 1972 and running roughly 4000 km east to west. Clearance spreads outward from the roads in the "fishbone" pattern visible from satellites.
• Hydroelectric dams, including Tucuruí on the Tocantins and Belo Monte on the Xingu, which flooded large areas of forest.
• Settlement and government resettlement schemes moving landless families into the interior.

The rate of loss. Brazil's National Institute for Space Research, INPE, measures Amazon clearance every year from satellites. The annual figure peaked at roughly 27,800 km² in 2004, fell to roughly 4,600 km² by 2012 as enforcement tightened, and rose again to roughly 13,000 km² in 2021. Quote these as approximate and attribute them to INPE.

Effects on the local natural environment. Habitat destroyed and jaguar and harpy eagle populations fragmented; soil erosion and leaching on cleared land, which is often exhausted within a few harvests and abandoned; rivers silted and polluted, including mercury contamination from gold mining; increased overland flow and local flooding; smoke from burning severe enough to close airports in Amazonian cities.

Effects on the global natural environment. The Amazon is one of the world's largest carbon stores, and clearance plus burning releases that carbon and reduces future absorption, feeding the enhanced greenhouse effect. The forest also recycles its own rainfall through transpiration, so large scale clearance reduces rainfall over a much wider region of South America.

Effects on people. Indigenous groups have lost territory, been exposed to introduced disease, and come into violent conflict with loggers and ranchers. Against that, ranching, soy, mining and timber generate export earnings and jobs, which is exactly why the clearance continues.

13b. Hot desert: the Sahara, North Africa

Location and scale. The Sahara is the largest hot desert in the world, covering roughly 9 million km² across North Africa, from the Atlantic to the Red Sea. It spans eleven countries including Algeria, Libya, Egypt, Sudan, Chad, Niger, Mali, Mauritania, Morocco and Tunisia, and lies on and around the Tropic of Cancer.

Climate, using In Salah and Nouakchott. Cambridge has set both stations. In Salah, deep inland in central Algeria, has a mean May temperature of 30 °C and a mean annual temperature range of 23.5 °C, with rain in most months at or near zero. Nouakchott, on the Atlantic coast of Mauritania, is markedly more moderate: cooler in summer, warmer in winter, with a smaller range and a little rain in August and September. The difference is distance from the sea, plus the moderating effect of the cold Canary Current offshore. Across the Sahara annual rainfall is under 250 mm everywhere and under 25 mm in the driest interior, summer daytime temperatures above 45 °C are routine, and nights can fall close to freezing.

Why it is so dry. The Sahara sits under the descending limb of the Hadley cell, so high pressure and sinking, warming air suppress cloud formation. The northeast trade winds reach it after crossing the whole width of Asia and Arabia and arrive dry. The interior is thousands of kilometres from any ocean. The cold Canary Current cools the air on the western coast so that condensation happens offshore as fog rather than inland as rain. The Atlas Mountains cast a rain shadow across the northwest.

Landscape. Not all sand. Ergs (sand seas such as Erg Chebbi in Morocco and the Grand Erg Oriental in Algeria) make up only a minority of the surface. Most is reg (stony plain) and hamada (bare rock plateau), cut by dry wadis and broken by the Ahaggar and Tibesti mountain ranges. Water reaches the surface at oases, fed from aquifers.

Soil. Thin, sandy or stony, alkaline, very low in organic matter, and often carrying a salt crust left where capillary water has evaporated at the surface. Easily blown away once disturbed.

Vegetation. Sparse, low and widely spaced. Date palms at oases, acacia and tamarisk trees along wadis where groundwater is closer to the surface, halfa grass, cram cram and drought resistant shrubs on open ground, and ephemerals that appear and flower within days of rare rain. All the xerophytic adaptations in section 10 are visible here: tap roots reaching to groundwater, waxy and reduced leaves, dormancy, and wide spacing.

Wildlife. Dromedary camel, able to go for long periods without drinking, with wide feet for soft sand and nostrils that close against blown sand. Fennec fox, with very large ears that radiate heat and a nocturnal, burrowing habit. Addax antelope and dorcas gazelle, which get most of their water from plants. Jerboa, which burrows by day and produces highly concentrated urine. Horned viper, scorpions and desert monitor lizards, all of which shelter in burrows or under rock through the heat of the day.

How the four elements link.

1. under 25 mm of rain a year and daytime heat above 45 °C
2. only widely spaced xerophytes survive
3. very little leaf litter reaches the ground
4. the soil holds almost no organic matter and stays infertile and saline
5. sparse plants support only a small number of highly specialised animals
6. those animals depend on plants for both food and water
7. biomass and biodiversity stay low, and recovery from any damage is extremely slow.

People. Oasis settlements growing dates and irrigated crops, nomadic pastoralists such as the Tuareg herding camels and goats, and modern oil and gas extraction in Algeria and Libya. The desert margin to the south, the Sahel, is where desertification pressure is greatest, though desertification itself belongs to syllabus point 3.7, not to 2.5.

If you were taught a different desert. The Sonoran and Mojave deserts of North America have appeared in Cambridge photographs, and they carry the best named flora and fauna: saguaro and organ pipe cactus, creosote bush, Joshua tree, kangaroo rat, Gila monster, roadrunner and rattlesnake. The Atacama is the strongest example for the cold current and rain shadow explanation. Any of these is acceptable, so long as you learn it in the same depth.

14. What the 7 mark questions have actually asked

Sixteen 7 mark questions on this topic were set between 2020 and 2024. Every one falls into one of five shapes, and knowing the shapes is worth more than any amount of general reading.

How the levels work. Every one of these mark schemes uses the same ladder:

• Level 1, 1 to 3 marks: simple statements with limited detail.
• Level 2, 4 to 6 marks: developed or linked statements, and a named example.
• Level 3, 7 marks: comprehensive and accurate statements including place specific detail.

The rule that costs the most marks. Most of these mark schemes carry the printed line "Max 5 if no named or inappropriate example". That is not the examiner's judgement, it is a rule. A perfectly correct answer with no named place is capped at 5 out of 7 by instruction. Some versions go further and print a maximum of 5 with no named places and a maximum of 6 with only one.

What place specific detail means here. The mark schemes spell it out: locational details, named places within the area, named flora and fauna, specific details of species lost, climate statistics, and dates. "The Amazon" is a named example. "Manaus has an annual temperature range of 1 °C and over 2000 mm of rain" is place specific detail. You need both.

One that scores zero. For a question on the effects of deforestation, the mark scheme states: "Logging or trees chopped down = 0". That is the cause, not the effect. Answer the question that was asked.

15. Common exam mistakes

• Confusing the two pressure systems. Equatorial is low pressure with rising air. Hot desert is high pressure with descending air. Getting these the wrong way round destroys every explanation that follows.
• Explaining equatorial rainfall as relief rainfall. It is convectional, and the mark scheme caps a relief answer at 2 marks.
• Saying equatorial areas have no variation in rainfall. Temperature barely varies; rainfall does, and one mark scheme was built entirely around that distinction.
• Answering a local effects question with global ones (global warming, melting ice, rising sea level), or a global question with local ones. Mark schemes list the wrong scale explicitly as not credited.
• Giving the cause of deforestation when the question asks for the effect. "Trees are chopped down" scores zero on an effects question.
• Naming a plant or animal without an adaptation. "Cacti" earns nothing. "Cacti have fleshy stems that store water" earns the mark.
• Describing a feature without saying what it does, or explaining a function without naming the feature. Both halves are required, and the mark schemes say so.
• Writing about managing deforestation. This syllabus point asks for causes and effects only. Management belongs to 3.7.
• Reading the rainfall bars when the question asked for the temperature line, or the reverse.
• Not showing the working on a temperature range calculation, which loses one of the two marks.
• Justifying a climate graph choice after choosing the wrong graph. The mark scheme refuses all the reasons if the choice is wrong.
• Naming a country when the question asked for a named area.
• Confusing attrition style vocabulary errors here too: transpiration is water lost from plants, evaporation is from open water and soil, and evapotranspiration is the two combined. One mark scheme accepts evapotranspiration as an alternative to the pair but not as well as it.
• Forgetting that the largest nutrient store in a rainforest is the vegetation, not the soil.

16. Quick revision

• Equatorial: about 27 °C every month, annual range 1 to 3 °C, over 2000 mm of rain, rain in every month, low pressure, convectional, daily afternoon storms.
• Hot desert: under 250 mm of rain a year, hottest month often 30 to 50 °C, large annual range (In Salah 23.5 °C) and very large diurnal range, high pressure, clear skies.
• Rainforest distribution: on and near the Equator, within about 10 degrees, in South America, Central America, Central Africa and Southeast Asia.
• Hot desert distribution: on and near the Tropics, about 5 to 30 degrees north and south, mostly on the west sides of continents.
• Six low rainfall reasons for deserts: high pressure and descending air, distance from the sea, dry trade winds, rain shadow, cold ocean currents, no water or vegetation to evaporate.
• Convection chain: heating → evaporation and transpiration → rising air → cooling → condensation → saturation → heavy rain.
• Rainforest layers: emergents 40 to 60 m, canopy 25 to 40 m, under canopy, shrub layer and forest floor.
• Rainforest adaptations: buttress roots for support, drip tips to shed heavy rain, shallow wide roots for surface nutrients, lianas and epiphytes to reach light.
• Nutrient cycle: the largest store is the vegetation. Nutrients enter from rain and weathered rock, and leave by leaching and runoff. The soil is poor.
• Desert adaptations: tap roots or wide shallow roots, fleshy water storing stems, spines instead of leaves, waxy cuticles, sunken stomata, dormancy, light colours, wide spacing.
• Desert animals: nocturnal, burrowing, large ears to lose heat, concentrated urine, water from food.
• Deforestation causes: cattle ranching (South America), smallholder farming (Africa), large scale agriculture (Asia), plus logging, mining, roads, dams and settlement.
• Local effects: habitat loss, extinction, soil erosion, leaching, overland flow, flooding, siltation.
• Global effects: less carbon dioxide absorbed, more released by burning, enhanced greenhouse effect, global warming, melting ice, rising sea level, changed rainfall patterns.
• Effects on people: loss of land, culture and resources for indigenous groups, introduced disease, conflict, and against that, jobs and economic development.
• Two case studies required: one area of tropical rainforest and one area of hot desert.
• A named example lifts you to Level 2. Place specific detail buys the seventh mark. Without a named example the mark scheme caps you at 5.

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