OCR GCSE (9-1) Geography A: Geographical Themes (J383) · Spec 2.3.1, 2.3.2 and 2.3.3
Climate change: evidence, causes and consequences
Read the notes, then try the questions. Each one is marked the moment you press Check, and shows the right answer and why.
Key ideas
- The Quaternary began about 2.6 million years ago. Cold glacials and warm interglacials have alternated. We are in an interglacial now.
- In the last thousand years there was a medieval warm period, then the Little Ice Age (about 1300 to 1850), then modern warming since the late 1800s.
- Evidence: thermometer records since about 1850, ice cores, tree rings, and old paintings and diaries. Ice cores trap air bubbles that record past carbon dioxide and go back hundreds of thousands of years.
- Paintings and diaries are local and may be biased, so they are less reliable than measurements.
- Natural causes: changes in the sun's output, changes in the Earth's orbit (eccentricity, tilt, wobble) and volcanic eruptions. Ash and sulphur dioxide reflect sunlight and cool the planet for a year or two.
- Human cause: the enhanced greenhouse effect. Burning fossil fuels, cutting down forests and farming add greenhouse gases. They absorb heat leaving the Earth and send some back down.
- Consequences: rising temperatures, sea-level rise, melting ice, more heatwaves and heavy rain, drought and coral bleaching.
Key terms
- Glacial
- A cold period when ice sheets spread.
- Interglacial
- A warm period between glacials.
- Ice core
- A tube of ice drilled from an ice sheet. Trapped air in it shows past atmospheres.
- Greenhouse gas
- A gas such as carbon dioxide or methane that traps heat in the atmosphere.
- Mitigation
- Reducing the causes of climate change.
- Adaptation
- Adjusting to the effects of climate change.
Common mistakes
- Saying volcanic ash warms the planet. Ash and sulphur dioxide cool it for a short time.
- Saying ice cores go back millions of years. They go back hundreds of thousands of years.
- Explaining the greenhouse effect by listing the gases. The explanation is the mechanism: gases trap heat that is leaving the Earth.
- Thinking mitigation and adaptation are the same. Mitigation tackles the causes. Adaptation copes with the effects.
Exam tip
On a 'describe the relationship' question worth 2 marks, one mark is for naming it, such as positive correlation, and one is for describing how the two things change using data. The opposite statement, such as 'they also fall together', earns nothing more. An 'evaluate' question on reliability needs strengths and limitations of the evidence.
Free practice questions
7 questions, 14 marks. Answer, then press Check. The marking guide explains how the marks are worked out. Nothing is saved.
- Question 1 · Multiple choice[1 mark]
How do greenhouse gases warm the Earth's atmosphere?
- Question 2 · Fill the gaps[2 marks]
Burning ___ fuels releases carbon dioxide, which strengthens the ___ effect.
Word bank: ozone · fossil · greenhouse
- Question 3 · Matching[3 marks]
Match each term to its meaning.
- Question 4 · True or false[3 marks]
Decide whether each statement about evidence for climate change is true or false.
1. Ice cores hold trapped air that shows past atmospheres.
2. Tree rings give clues about past growing conditions.
3. Thermometer records cover the whole of the last 2.6 million years.
- Question 5 · Sort into groups[3 marks]
Sort each cause of climate change into natural or human.
Volcanic eruptions
Changes in the Earth's orbit
Burning coal for electricity
- Question 6 · Put in order[1 mark]
Put these steps in order, starting with the human activity.
Use the arrows to put these in the right order, first at the top.
- 1Sea level rises
- 2Ice melts and warming oceans expand
- 3More heat is trapped in the atmosphere
- 4Global temperatures rise
- 5Fossil fuels are burned and release CO2
- Question 7 · Multiple choice[1 mark]
The 1815 eruption of Mount Tambora in Indonesia was a VEI 7 event. How do very large eruptions affect global temperature for a year or two?