Atmospheric processes and global climate change
Explain energy budgets and atmospheric circulation, connect moisture processes to precipitation, and evaluate climate evidence and causes.
Exam scope and assessment notes
Cambridge International AS & A Level Geography 9696, 2027–2029 syllabus, Topic 2. Across every topic, practise reading both quantitative and qualitative geographical resources, describing patterns before explaining them, evaluating evidence and producing a structured, supported conclusion. These original explanations and self-checks are independent study support, not Cambridge questions, official marks or grades. Centre-selected named examples and detailed case studies still need course-specific evidence packs. Full timed mock papers, official marking or grade prediction, and human subject-teacher review are not provided. Fieldwork is not assessed in this syllabus, but this site does not collect or supervise primary data.
Before you begin
- Cambridge recommends prior Geography at approximately Cambridge IGCSE or Cambridge O Level. Read the source and its scale before explaining patterns; support evaluation with relevant evidence.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Is sunlight mainly incoming shortwave or outgoing longwave radiation?
What you will learn
- Account for shortwave and longwave energy inputs, transfers and outputs
- Explain global and seasonal patterns of energy transfer
- Relate atmospheric moisture processes to precipitation and weather
- Evaluate proxy and instrumental evidence and compare physical with human climate influences
Energy is received, transferred and returned
Incoming shortwave solar radiation is partly reflected, scattered or absorbed. Earth's surface emits longwave terrestrial radiation. Albedo describes the proportion reflected; greenhouse gases absorb and re-emit some longwave radiation as back radiation. Sensible heat warms air directly, while latent heat moves energy through evaporation and condensation.
Low latitudes tend to have an energy surplus and high latitudes a deficit. Hadley, Ferrel and Polar cells, the ITCZ, wind belts, jet streams and ocean gyres redistribute energy. Their patterns vary with season, latitude, land–sea distribution and currents. Day and night also change surface energy budgets; do not describe the global mean as if every place receives the same energy.
Moisture changes phase and air is lifted
Evaporation, condensation, freezing, melting and sublimation move water between states. Air may be lifted by surface heating (convection), fronts or topography (orographic uplift); cooling can cause condensation and precipitation. Rain, snow, hail, dew and fog depend on temperature and the atmospheric conditions, not just the name of the uplift process.
A climate explanation links energy, moisture and circulation while distinguishing local weather from longer-term climate. A diagram should show the direction of energy or air movement and name the process rather than relying on arrows alone.
Climate claims need multiple kinds of evidence
Ice cores, tree rings and fossils provide proxy evidence for past climate. Instrumental records extend back to the nineteenth century; sea-level rise, sea-ice reduction and shrinking ice sheets or glaciers provide other evidence. Each source has a time span, resolution and uncertainty, so compare independent lines of evidence.
Greenhouse gases differ in concentration, atmospheric lifetime and global-warming potential; carbon-dioxide equivalence helps compare their warming effect. Solar output, volcanic eruptions and ENSO can affect energy budgets; human emissions, changes to carbon storage and altered surface albedo also matter. Explain how the enhanced greenhouse effect changes the global budget, and avoid claiming that one cold day or one proxy proves or disproves a long-term trend.
Sources for this lesson
Pause and explain
Why is a long instrumental record stronger evidence of a climate trend than one unusual day?
Worked example
At one location, 300 W/m² of shortwave radiation arrives, 90 W/m² is reflected and 190 W/m² of longwave radiation leaves. Estimate the net radiative balance using these supplied values.
Show the worked solution
- Absorbed shortwave = 300 − 90 = 210 W/m².
- Net radiative balance = absorbed shortwave − outgoing longwave = 210 − 190.
- State the sign: the supplied radiative balance is positive before any other transfers are considered.
Answer Net radiative balance = +20 W/m². This simplified result omits other energy transfers and time variation.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A diagram shows rising warm air at the equator and sinking air near 30° latitude. Name the circulation cell and explain one way it can influence rainfall.
Give me a hint
Identify the tropical cell, then link rising or sinking motion to moisture and condensation.
Compare my reasoning
- The circulation is the Hadley cell.
- Warm air near the equator rises; cooling can promote condensation and rainfall near the ITCZ.
- Descending air near the subtropics is generally drier, though local conditions and season also matter.
The Hadley cell transfers energy from the tropics. Rising air near the ITCZ can cool and condense, while subtropical descent is often associated with drier conditions.
Look for these in your work
- Cell named
- Vertical motion connected to moisture
- Pattern qualified
A mountain region receives more precipitation on its windward slope than on its leeward slope. Explain the pattern and name one limit to the explanation.
Give me a hint
Track moist air up and over relief, including cooling and descent.
Compare my reasoning
- Moist air is forced up the windward slope and expands as pressure falls.
- Cooling can cause condensation and precipitation on the windward side.
- Descending air on the leeward side warms and may be drier; wind direction and moisture supply affect the strength of the rain shadow.
Orographic uplift and cooling encourage windward precipitation; descending air can create a drier leeward rain shadow, depending on wind and moisture conditions.
Look for these in your work
- Uplift and cooling explained
- Windward/leeward distinction
- A condition named
Assess the claim that recent global warming is either entirely natural or entirely caused by one human activity.
Give me a hint
Compare instrumental and proxy evidence with several physical and anthropogenic influences.
Compare my reasoning
- Use long-term temperature records alongside independent evidence such as sea level, sea ice or glacier change.
- Consider solar variability, volcanic activity and ENSO, then assess greenhouse-gas emissions, carbon storage and albedo changes.
- A sound conclusion compares magnitude, timing, mechanism and uncertainty; it should avoid attributing a complex trend to one cause without evidence.
Both absolute claims are too simple. Multiple evidence sources establish the pattern; physical factors affect climate, while human activities alter greenhouse-gas concentrations and energy storage. A conclusion should compare their mechanisms and evidence over the relevant timescale.
Look for these in your work
- More than one evidence type
- Physical and human factors considered
- Conclusion qualified by scale and uncertainty
Common mistakes
- Treating back radiation as incoming solar radiation
- Confusing local weather with long-term climate
- Assuming the three-cell model predicts every local wind
- Treating one proxy as a complete climate record
- Ignoring non-human factors or overstating them as an alternative to all human influence
What can you explain now?
Which process transfers latent heat from a surface into the atmosphere: evaporation or reflection?
Compare with the explanation
Evaporation
Evaporation moves water and latent energy into the atmosphere; reflection changes the radiation returned from a surface.
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Make it stick
Distinguish the natural greenhouse effect from the enhanced greenhouse effect, and name two independent ways to examine a climate trend.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.