Rising emissions and the enhanced greenhouse effect

The enhanced greenhouse effect

The natural greenhouse effect keeps Earth habitable: greenhouse gases absorb outgoing long-wave radiation and re-emit some back towards the surface. Adding more gases enhances this effect, trapping more heat.

• Carbon dioxide (CO2): burning fossil fuels, cement, deforestation.
• Methane (CH4): livestock, rice paddies, landfill, leaks from oil, gas and coal.
• Nitrous oxide (N2O): nitrogen fertilisers, industry.

At Mauna Loa, annual mean CO2 rose from 316.91 ppm (1960) to 338.76 (1980), 369.71 (2000), 390.10 (2010), 414.21 (2020) and 421.08 ppm (2023) (NOAA GML).

Who emits? Total, per capita and over time

IEA data for 2023:

• China emitted about 35% of global energy-related CO2, 15% more than all advanced economies combined; its per capita emissions passed the advanced-economy average in 2020 and are now 15% higher, though still about one third below the United States.
• India passed the EU as the third-largest emitter, but its per capita emissions (about 2 tonnes) are under half the global average.
• Developing Asia produces about half of global emissions, up from about one quarter in 2000.

Developed countries have the largest historical emissions; emerging economies now dominate growth; developing countries emit little per person.

Using the data

Skill (4) in this context means analysing atmospheric composition data. When describing a CO2 graph: state the overall trend, quote values with dates, calculate the change or rate, and note the seasonal zigzag (plants take up CO2 in the northern summer).

Examiners in June 2025 found a fundamental misunderstanding of per capita (emissions per person): some candidates wrote about population size or total emissions instead. Read the question carefully.

Worked example

Calculate the percentage increase in annual mean CO2 at Mauna Loa from 1960 (316.91 ppm) to 2023 (421.08 ppm).

1. Increase = 421.08 - 316.91 = 104.17 ppm
2. 104.17 / 316.91 x 100

Answer: About 32.9%.

Check yourself

1. Mauna Loa annual mean CO2 was 316.91 ppm in 1960 and 421.08 ppm in 2023. Calculate the percentage increase to 1 decimal place.
   Show answer

   32.9 %. 104.17 / 316.91 x 100 = 32.9%.

2. CO2 was 390.10 ppm in 2010 and 414.21 ppm in 2020. Calculate the mean rate of increase in ppm per year, to 2 decimal places.
   Show answer

   2.41 ppm per year. 24.11 / 10 = 2.41 ppm per year.

3. CO2 was 316.91 ppm in 1960 and 338.76 ppm in 1980. Calculate the mean rate of increase in ppm per year, to 2 decimal places.
   Show answer

   1.09 ppm per year. 21.85 / 20 = 1.09 ppm per year, slower than in 2010 to 2020.

4. Which is a major source of methane?
   • Wind turbines
   • Livestock and rice paddies
   • Nuclear power
   • Planting forests
   Show answer

   Livestock and rice paddies. Digestion in cattle and waterlogged rice fields release methane.

5. India passed the EU as the third-largest emitter in 2023, but its per capita emissions are under half the global average. This is because
   • India emits no CO2 from coal
   • per capita counts only industry
   • the EU has a larger population than India
   • India's very large population divides its total among many people
   Show answer

   India's very large population divides its total among many people. Per capita = total / population.

6. According to the IEA, about what share of global energy-related CO2 came from China in 2023?
   • 5%
   • 35%
   • 60%
   • 15%
   Show answer

   35%. IEA: China accounts for 35% of global CO2 emissions.

7. Explain why per capita emissions are usually higher in developed countries than in developing countries.
   Show answer

   People in developed countries have higher incomes and consume more energy for cars, heating, air conditioning and goods, much of it from fossil fuels, while many people in developing countries use little energy.. Higher incomes mean more fossil-fuel energy use per person.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Geography specification (Issue 3, September 2025)
• NOAA Global Monitoring Laboratory: Mauna Loa annual mean CO2 data file
• IEA: CO2 Emissions in 2023, the changing landscape of global emissions (2024)
• Pearson principal examiner report, WGE01 Global Challenges, June 2025

Last updated 8 November 2026. Spotted a mistake? Tell us.