The layer of gases around Earth, mainly nitrogen (78%) and oxygen (21%).
Troposphere
The lowest layer, where weather occurs.
Stratosphere
Above the troposphere; contains the ozone layer.
Greenhouse effect
Greenhouse gases absorb and re-emit infrared radiation, warming the lower atmosphere.
Albedo
The proportion of incoming radiation a surface reflects.
The atmosphere is a dynamic system with inputs and outputs of gases and energy.
The full notes, worked example and check questions for this subtopic are in the app.
Exam tip: The greenhouse effect is not the same as ozone depletion: don't mix them up in answers.
6.2Climate change: causes and impacts
Key terms
Climate change
Long-term change in global or regional climate patterns.
Global warming potential (GWP)
How much heat a gas traps compared with CO₂ over a set time.
Feedback loop
A process that amplifies (positive) or reduces (negative) warming.
Tipping point
A threshold beyond which change becomes self-sustaining (e.g. ice sheet collapse).
Evidence: rising CO₂ (over 420 ppm), global temperature about 1.2 °C above pre-industrial levels, sea-level rise, melting glaciers and sea ice, ice cores showing CO₂ and temperature linked over 800 000 years.
The full notes, worked example and check questions for this subtopic are in the app.
Exam tip: Support claims with data (ppm, °C, sea-level rise) where possible: precise evidence lifts an answer to the top band.
6.3Climate change: mitigation and adaptation
Key terms
Mitigation
Reducing greenhouse gas emissions or increasing sinks to limit climate change.
Adaptation
Adjusting to the effects of climate change.
Carbon capture and storage (CCS)
Capturing CO₂ from power stations or air and storing it underground.
Paris Agreement
2015 treaty aiming to limit warming to well below 2 °C, ideally 1.5 °C.
Mitigation: renewable energy, energy efficiency, electric transport, reforestation, carbon taxes and trading, CCS, diet change, reducing waste.
The full notes, worked example and check questions for this subtopic are in the app.
Exam tip: Classify every strategy as mitigation or adaptation before evaluating it. Mixing them up is a frequent error.
6.4Stratospheric ozone
Key terms
Ozone layer
Ozone (O₃) in the stratosphere that absorbs harmful UV radiation.
Ozone-depleting substances (ODS)
Chemicals such as CFCs and halons that destroy ozone.
Montreal Protocol
1987 treaty phasing out ODS: the most successful environmental agreement.
UV radiation
High-energy radiation that damages DNA, causing skin cancer and cataracts.
Ozone is constantly formed and broken down by UV radiation in a dynamic equilibrium.
The full notes, worked example and check questions for this subtopic are in the app.
Exam tip: Keep the ozone hole and global warming separate, but mention the link through HFCs and the Kigali Amendment.