To interpret a dataset, read what each column measures, find the difference you need, calculate it correctly, and then describe it in one precise sentence. The figures in exam questions are supplied, so accuracy and wording earn the marks.
This lesson builds on separating a trend from attribution.
What should you check before calculating?
Look at the title, the units and the years first. Emissions might be in million tonnes of carbon dioxide, and temperature in °C. Then check whether the table gives totals, per person values, or both.
Wrong answers come from using the wrong column more than from wrong arithmetic. Underline the column you will use before you start.
How do you calculate and describe change?
- Absolute change: final value minus starting value.
- Percentage change: absolute change ÷ starting value × 100.
- Per person value: total ÷ population, keeping the units consistent.
- Sentence: state the variable, the period, the starting and final values, and the size of change.
Worked example
The data are invented for practice, for an imaginary country.
| Year | Emissions (million tonnes CO₂) | Population (millions) |
|---|---|---|
| 2000 | 400 | 20 |
| 2010 | 460 | 22 |
| 2020 | 506 | 25 |
Total change 2000 to 2020: 506 − 400 = 106 million tonnes.
Percentage change: 106 ÷ 400 = 0.265, so 26.5%.
Per person in 2000: 400 ÷ 20 = 20 tonnes. Per person in 2020: 506 ÷ 25 = 20.24 tonnes.
Per person change: 0.24 ÷ 20 = 0.012, so 1.2%.
Sentence: “Total emissions rose by 26.5% between 2000 and 2020, but emissions per person rose by only 1.2%, because the population grew by 25%.” The population check: 5 ÷ 20 = 0.25. This explains most of the rise in the total.
The mistake to watch for
Mistaken answer: “Emissions rose 15% from 2000 to 2010, then 10% from 2010 to 2020, so they rose 25% overall.”
The two percentages use different starting values, 400 and 460.
Check the two periods: 60 ÷ 400 = 15% and 46 ÷ 460 = 10%.
Both are correct on their own. The overall change goes from 400 to 506, which is 26.5%, not 25%. Adding percentages loses the effect of the changing base.
Check yourself
1. Emissions rise from 300 to 330 million tonnes. Calculate the percentage change.
Show answer
330 − 300 = 30. Then 30 ÷ 300 = 0.1, so 10%.
2. Emissions fall from 500 to 450 million tonnes. Calculate the percentage change.
Show answer
450 − 500 = −50. Then 50 ÷ 500 = 0.1, so a 10% decrease. Give the direction in words.
3. A country emits 150 million tonnes with a population of 10 million. Find the emissions per person.
Show answer
150 ÷ 10 = 15 tonnes per person. Check: 15 × 10 = 150.
Where this leads next
Once the calculations are steady, read how the greenhouse effect is explained as a mechanism. Try your own small data in the statistics and distribution explorer.
Students lose marks here for sentences that hold the right numbers but never state the period or units. A teacher in online one-to-one Geography tuition can check that wording against your own working.