Try this 15-question A level quiz to see how much you know about the carbon cycle, its stores, sinks and the place of the lithosphere, atmosphere and cryosphere in the system.

If you haven't already done them, work through the ‘Carbon cycle’ and ‘Peatlands and the carbon cycle’ units to find out more. Or look at them again to help fill in any gaps in your knowledge about the carbon cycle.

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QUIZZES // The carbon cycle

Q1. Which one of these processes takes carbon dioxide out of the atmosphere?





Q2. Which one of these processes releases carbon dioxide into the atmosphere?





Q3. Which one of the following is the largest store (or sink) of carbon?

The biosphere

The atmosphere

The lithosphere

The hydrosphere

Q4. Which one of these carbon stores is the soil store?

The lithosphere

The cryosphere

The biosphere

The pedosphere

Q5. Carbon is often measured in GtC – a gigatonne of carbon dioxide. How much is a gigatonne?

One thousand tonnes

One hundred thousand tonnes

One million tonnes

One billion tonnes

Q6. Which one of these terrestrial ecosystem’s soil stores the most carbon?

Boreal moist

Boreal dry

Tropical moist

Tropical dry

Q7. Annual fluctuations in the concentration of atmospheric CO2 naturally occur because of which one of the following?

Plants respire all the time but photosynthesis stops when it gets dark

Volcanic activity increases in winter

Northern hemisphere plants lose their leaves in winter, reducing photosynthesis

Human activities produce more CO2 in winter

Q8. What percentage of the atmosphere is carbon dioxide?





Q9. In the slow carbon cycle (long-term carbon cycle) how long does it take for carbon to move between the rock, soil, ocean and atmosphere?

Between 1 and 2 million years

Between 10 and 20 million years

Between 100 and 200 million years

Between 1 billion and 2 billion years

Q10. What is the term given to describe natural CO2 outgassing events, such as occurred in Lake Nyos, Cameroon, in 1986?

Hydrothermal eruption

Phreatomagmatic eruption

Limnic eruption

Plinian eruption

Q11. What do negative emission schemes aim to do?

Create a new carbon sink / amplify the actions of an old carbon sink

Reduce carbon emissions from human activities through economic incentives

Reduce carbon emissions from human activities through changes in legislation

Provide geoengineering solutions to global warming, e.g. spraying sunlight-reflecting aerosols into the lower atmosphere

Q12. Peatlands are an important global store of carbon – globally, they account for about 650 GtC. Where are most of the world’s peatlands located?

Sub-Saharan Africa

Amazon River basin


Northern Europe, Russia, Canada and Alaska

Q13. What does the term ‘global carbon budget’ refer to?

The total amount of carbon in all global carbon stores

The amount of carbon in the atmosphere

How much carbon is emitted compared to how much is absorbed

The measurement of the transfer of carbon between the land and the oceans

Q14. Which one of the following terms would be crucial to use in explaining why peatlands accumulate carbon?


Anaerobic conditions

Carbon source

Carbon density

Q15. Which of the following processes takes the most carbon (120 GtC) out of the atmosphere?

Plant respiration

Plant photosynthesis

Ocean uptake

Litter fall


You scored this time. The more correct answers you give, and the fewer incorrect answers you guess, the better your score.

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