Theme 2: The Natural Environment — Weather and Climate

What you'll learn

This revision guide covers everything you need to know about weather and climate for CIE IGCSE Geography. You'll master the difference between weather and climate, understand atmospheric processes including pressure systems and air masses, and learn about precipitation types and formation. The guide also covers climate graphs, factors affecting temperature and rainfall, and global climate zones — all tailored to what examiners actually test.

Key terms and definitions

Weather — the state of the atmosphere at a specific place and time, including temperature, precipitation, wind speed and cloud cover

Climate — the average weather conditions recorded over a period of at least 30 years for a particular region

Precipitation — any form of water (liquid or solid) that falls from the atmosphere to the Earth's surface, including rain, snow, sleet and hail

Air mass — a large body of air with similar temperature and humidity characteristics throughout, acquiring these properties from the surface over which it forms

Frontal rainfall — precipitation formed when a warm air mass meets a cold air mass, forcing the warm air to rise and cool

Convectional rainfall — precipitation caused by intense heating of the Earth's surface, leading to rising air currents that cool and condense

Anticyclone — an area of high atmospheric pressure with descending air, typically bringing settled, dry weather

Depression — an area of low atmospheric pressure with rising air, associated with unsettled weather, clouds and precipitation

Core concepts

Weather vs Climate

Weather refers to short-term atmospheric conditions — what you experience hour-by-hour or day-by-day. Climate describes long-term patterns and averages calculated over decades.

Key differences:

• Weather changes rapidly; climate changes gradually over years
• Weather is measured at a specific moment; climate uses statistical averages
• Weather forecasts cover days ahead; climate projections span decades

Weather elements measured include:

• Temperature (thermometer, measured in °C)
• Precipitation (rain gauge, measured in mm)
• Wind speed (anemometer, measured in km/h or knots)
• Wind direction (wind vane, recorded as compass direction)
• Cloud cover (visual observation, measured in oktas)
• Atmospheric pressure (barometer, measured in millibars/mb)
• Sunshine hours (Campbell-Stokes recorder)

Air masses and the UK's weather

The UK experiences weather influenced by five main air masses:

Polar Maritime (Pm)

• Source: Arctic/North Atlantic Ocean
• Characteristics: cold, moist air
• Weather: cool temperatures, heavy showers, good visibility

Tropical Maritime (Tm)

• Source: Atlantic Ocean near the Azores
• Characteristics: warm, moist air
• Weather: mild, cloudy, drizzly conditions

Polar Continental (Pc)

• Source: Northern Europe/Russia
• Characteristics: cold, dry air
• Weather: very cold in winter, warm and dry in summer

Tropical Continental (Tc)

• Source: North Africa/Mediterranean
• Characteristics: warm, dry air
• Weather: hot, dry conditions with heatwaves in summer

Arctic Maritime (Am)

• Source: Arctic Ocean
• Characteristics: very cold, moist air
• Weather: extremely cold with snow showers

Types of rainfall

Convectional rainfall

Formation process:

1. Intense solar heating warms the ground surface
2. Air in contact with the surface heats and expands
3. Warm air rises rapidly (convection currents)
4. Rising air cools at the dry adiabatic lapse rate (1°C per 100m)
5. Air reaches dew point and water vapour condenses
6. Cumulonimbus clouds form
7. Heavy rainfall occurs, often with thunder and lightning

Typical locations: Equatorial regions, UK summer afternoons

Characteristics: Short duration (1-2 hours), intense, localised, often in late afternoon

Frontal (cyclonic) rainfall

Formation process:

1. Warm air mass meets cold air mass at a front
2. Less dense warm air is forced to rise over denser cold air
3. Rising warm air cools and water vapour condenses
4. Layer clouds (nimbostratus) form along the front
5. Prolonged, steady rainfall occurs

Typical locations: Mid-latitude regions, UK throughout the year

Characteristics: Long duration (several hours/days), moderate intensity, widespread

Types of fronts:

• Warm front: warm air advancing, replacing cold air — gradual temperature rise
• Cold front: cold air advancing, undercutting warm air — sharp temperature drop
• Occluded front: cold front catches up with warm front — complex weather patterns

Relief (orographic) rainfall

Formation process:

1. Moist air is forced to rise over highland/mountain barriers
2. Air cools as it rises (adiabatic cooling)
3. Condensation occurs when dew point is reached
4. Clouds form on windward slope
5. Precipitation falls on windward side
6. Dry air descends on leeward side (rain shadow effect)

Typical locations: Western UK (Wales, Lake District, Scottish Highlands), windward slopes globally

Characteristics: Persistent, concentrated on windward slopes, creates rain shadow areas

Depressions and anticyclones

Depressions (low pressure systems)

Characteristics:

• Central pressure below 1000mb
• Air rises and cools
• Anticlockwise wind circulation in Northern Hemisphere
• Associated with frontal systems

Weather conditions:

• Thick cloud cover
• Precipitation (rain or snow)
• Strong winds
• Changeable temperatures
• Poor visibility

Sequence as depression passes UK (west to east):

1. Warm front approaches: pressure falls, cloud thickens, continuous rain
2. Warm sector: rain eases, mild temperatures, drizzle possible
3. Cold front passes: heavy rain/showers, sharp temperature drop, winds veer
4. After depression: clear skies, cooler, scattered showers

Anticyclones (high pressure systems)

Characteristics:

• Central pressure above 1013mb
• Air descends and warms
• Clockwise wind circulation in Northern Hemisphere
• Slow-moving systems

Summer weather:

• Clear skies and sunshine
• High daytime temperatures
• Light winds
• Early morning mist possible
• Dry conditions

Winter weather:

• Clear skies — rapid heat loss at night
• Very cold nights with frost
• Fog and freezing fog
• Low daytime temperatures
• Persistent cloud possible (anticyclonic gloom)

Factors affecting temperature

Latitude

• Lower latitudes (equatorial regions) receive more concentrated solar radiation
• Higher latitudes receive dispersed radiation at a low angle
• Equator averages 25-28°C; poles average below 0°C

Altitude

• Temperature decreases approximately 1°C per 100m gained
• Thinner air at altitude holds less heat
• Example: Mount Kenya (on equator) has permanent snow above 4,500m

Distance from the sea (continentality)

• Oceans heat and cool slowly; land heats and cool rapidly
• Maritime climates: smaller temperature range (e.g., UK — mild winters, cool summers)
• Continental climates: larger temperature range (e.g., Central Asia — cold winters, hot summers)

Ocean currents

• Warm currents raise coastal temperatures (e.g., North Atlantic Drift warming UK)
• Cold currents lower coastal temperatures (e.g., Benguela Current cooling Namibia coast)

Prevailing winds

• Winds from warm regions raise temperatures
• Winds from cold regions lower temperatures
• Tropical Maritime air warms UK in winter; Polar air cools it

Climate graphs and interpretation

Climate graphs display average monthly temperature (line graph) and precipitation (bar chart) for a location.

How to analyse climate graphs:

Temperature analysis:

• Identify highest and lowest months
• Calculate annual temperature range (highest month minus lowest month)
• Note hemisphere (Northern: July warmest; Southern: January warmest)

Precipitation analysis:

• Identify wettest and driest months
• Calculate total annual precipitation (sum all months)
• Identify seasonal patterns (wet/dry seasons or year-round rainfall)

Climate classification:

• Equatorial: High temperatures (25-28°C) year-round, rainfall every month (>2000mm/year)
• Tropical continental: High temperatures, distinct wet and dry seasons
• Hot desert: Very high temperatures, very low rainfall (<250mm/year)
• Mediterranean: Hot, dry summers; mild, wet winters
• Temperate maritime: Moderate temperatures, rainfall year-round (like UK)
• Temperate continental: Warm summers, cold winters, moderate rainfall
• Polar: Very cold year-round, low precipitation

Worked examples

Example 1: Explaining formation of frontal rainfall (4 marks)

Question: Explain how frontal rainfall is formed.

Mark scheme answer:

Frontal rainfall occurs when a warm air mass meets a cold air mass [1]. The warm air is less dense than the cold air [1], so it is forced to rise over the cold air mass [1]. As the warm air rises, it cools and the water vapour condenses [1], forming clouds and causing precipitation [1].

Examiner note: 4 marks available — any 4 well-developed points. Must show understanding of the process sequence.

Example 2: Interpreting a climate graph (6 marks)

Question: Study the climate graph for London, UK.

• Describe the temperature pattern shown [3]
• Describe the precipitation pattern shown [3]

Mark scheme answer:

Temperature (3 marks): The warmest month is July with approximately 18°C [1]. The coldest month is January with approximately 5°C [1]. The annual temperature range is about 13°C [1]. Temperatures rise from winter to summer / there is a clear seasonal pattern [1].

Precipitation (3 marks): Rainfall occurs throughout the year / every month receives precipitation [1]. Total annual precipitation is approximately 600mm [1]. The wettest months are October/November with about 65mm [1]. The driest months are February/March with about 40mm [1]. There is relatively little variation between months / fairly even distribution [1].

Examiner note: Award any 3 valid points for each section. Use specific data from the graph.

Example 3: Comparing weather in depressions and anticyclones (6 marks)

Question: Compare the weather associated with depressions and anticyclones in the UK.

Mark scheme answer:

Depressions bring unsettled weather with thick cloud cover [1], whereas anticyclones bring settled conditions with clear skies [1]. Depressions are associated with precipitation such as rain [1], while anticyclones bring dry weather [1]. Wind speeds are strong in depressions [1] but light in anticyclones [1]. Depressions have low atmospheric pressure (below 1000mb) [1], whereas anticyclones have high pressure (above 1013mb) [1]. In depressions, air rises [1], but in anticyclones air descends [1].

Examiner note: Award 1 mark per valid comparative point. Must compare, not just describe each separately.

Common mistakes and how to avoid them

• Confusing weather and climate — Remember: weather is day-to-day; climate is the 30-year average. Always use the correct term in your answer.

• Mixing up the three rainfall types — Create a clear revision table showing cause, process and typical location for convectional, frontal and relief rainfall. Don't describe one when asked about another.

• Failing to use data from climate graphs — Examiners want specific figures. Always quote temperatures in °C and precipitation in mm, not vague terms like "high" or "lots."

• Describing depressions and anticyclones without comparison — When asked to "compare," you must make direct links between the two (use "whereas," "in contrast," "while"). Simple separate descriptions score poorly.

• Forgetting the sequence in processes — Rainfall formation and frontal passages follow specific orders. Use numbered steps in revision to memorise the correct sequence.

• Confusing air mass source regions with weather impacts — Polar Maritime originates from cold regions but brings relatively mild conditions to UK in winter because it crosses warm ocean. Learn both source and resulting weather.

Exam technique for Theme 2: Weather and Climate

• Command word awareness: "Describe" requires stating what you observe (patterns, trends, data). "Explain" requires giving reasons and processes using connectives like "because," "this causes," "as a result." "Compare" demands you show similarities and differences explicitly.

• Using geographical terminology accurately: Examiners reward precise terms. Use "convectional rainfall" not "heat rain," "depression" not "low pressure thing," "adiabatic cooling" when describing air rising and cooling.

• Structuring process explanations: For formation processes (rainfall types, fronts), use a clear sequence: trigger → process → outcome. Number your points (1, 2, 3) to ensure logical order and help examiners follow your answer.

• Climate graph questions: Read the question carefully — separate marks are usually awarded for temperature description and precipitation description. Calculate ranges and totals before writing. Always include units and quote specific data values from the axes.

Quick revision summary

Weather describes short-term atmospheric conditions; climate is the 30-year average. The UK's weather results from five air masses (Polar Maritime, Tropical Maritime, Tropical Continental, Polar Continental, Arctic Maritime). Three rainfall types form differently: convectional (surface heating), frontal (air mass collision), relief (forced ascent over mountains). Depressions bring unsettled, wet, windy weather; anticyclones bring settled conditions (sunny in summer, cold/foggy in winter). Temperature varies with latitude, altitude, distance from sea, ocean currents and prevailing winds. Climate graphs show average monthly temperature and precipitation patterns, revealing climate type.