Two pages of bad news, and now the useful bit. If ecosystems can be turned into carbon sources by human activity, they can also be turned back into carbon sinks – and the biology of how that works is straightforward, even if the politics is not.
📚 What you need to know
Carbon sequestration is the capture and storage of carbon dioxide from the atmosphere.
It can be increased by boosting the removal of carbon into natural carbon sinks.
Forest regeneration (replanting cleared land) and afforestation (creating new forest) both store carbon in tree biomass.
Peat bogs store carbon because waterlogged, acidic conditions stop plant matter decomposing fully.
Draining and harvesting peat releases that carbon; restoring bogs allows them to sequester again.
NOS: scientists actively disagree about whether fast-growing non-native plantations or rewilding with native species is the better approach.
What sequestration means
Scientists think global warming can be slowed by increasing carbon sequestration. The definition is short, so learn it word for word.
DefinitionCarbon sequestration is the process of capturing and storing carbon dioxide from the atmosphere.
In practice this means increasing the amount of carbon moving out of the atmosphere and into natural carbon sinks. There is hope that artificial carbon storage will become viable at some point, but you should be clear in an exam that it is still at the research stage. Everything usable today is biological.
These are the same sinks that appeared on the causes page. Protecting them and building them up is the whole of natural sequestration.
Forest regeneration and afforestation
Two words that sound similar and mean different things, so get them straight now.
Term
What it means
Forest regeneration (reforestation)
Planting new trees in areas that have been deforested – putting forest back where forest used to be
Afforestation
The creation of new forest in an area that did not previously have it
The biology behind both is simply photosynthesis running for a long time. If trees are allowed to grow to maturity, they can store huge amounts of carbon in their biomass. The carbon that was carbon dioxide in the air ends up as cellulose and lignin in the trunk, and it stays there for as long as the tree does.
Costa Rica is the example to quote: the country now plants around seven times as many trees as it cuts down, which shows that lost forest really can be restored. It is worth adding the honest caveat, because examiners like it – achieving this needs large government inputs, usually in the form of payments and benefits to landowners. Trees are cheap; persuading people not to clear land is not.
Peat bog restoration
To understand why peat bogs matter, you have to understand why the plant matter in them never finishes decomposing.
Peat forms when dead plant matter cannot decompose fully, because the ground is waterlogged – and therefore anaerobic – and acidic. Decomposers cannot work properly in those conditions, so the plant material only partly breaks down and accumulates as peat, year after year. The carbon locked into that partly decomposed matter is what makes peat bogs an essential carbon sink. Peatlands form in boreal and temperate ecosystems, and can form rapidly in tropical ones.
Human activity releases that store in two main ways. Peat is harvested for fuel, and bogs are drained so the land can be used for development or agriculture. Both routes return carbon to the atmosphere – the first by combustion, the second by decomposition.
The draining part is worth thinking about carefully. Bogs are drained by digging drainage ditches so the land dries out. As the peat dries, the waterlogged anaerobic conditions disappear, and the activity of decay organisms increases. The bog does not need to be dug up to lose its carbon; it just needs to be dried.
A drained bog is not a neutral piece of ground – it is actively leaking carbon that took thousands of years to accumulate.
Restoration is therefore about water, not planting. Filling in drainage ditches and regulating peat harvesting allows bogs to recover and to continue growing in depth, which increases their ability to sequester carbon.
Notice the pattern. Both sequestration methods on this page work by restarting a natural process that human activity had interrupted – photosynthesis in one case, incomplete decomposition in the other. Neither invents anything new. That is exactly why they are described as naturally occurring ecosystem processes.
NOS: an argument scientists are still having
Scientists do not always agree on the best way to do something, and different approaches can bring different benefits and different problems. Carbon sequestration by tree planting is a live example, and the syllabus expects you to be able to present both sides fairly.
Approach
The argument for it
The trade-off
Plantations of non-native trees
Fast-growing species sequester the maximum mass of carbon in the shortest time, which matters if the goal is to slow warming quickly
A plantation is not a natural ecosystem, so the benefit for biodiversity is limited
Rewilding with native species
Encouraging native species restores naturally occurring ecosystems, which is likely to be better for biodiversity
Carbon is sequestered more slowly, so the climate benefit arrives later
In a NOS question you are not being asked which side is right. You are being asked to show that you understand why reasonable scientists can look at the same goal and disagree about the method. Give both positions, name the trade-off between them, and stop there.
Worked examples
WE 1
Define and apply
Define carbon sequestration, and outline how forest regeneration increases it. (3 marks)
Step 1: the definition
Carbon sequestration is the process of capturing and storing carbon dioxide from the atmosphere.
Step 2: what regeneration is
Forest regeneration means planting new trees in areas that have been deforested.
Step 3: the mechanism
Those trees take in carbon dioxide by photosynthesis and, if allowed to grow to maturity, store large amounts of carbon in their biomass.
Photosynthesis moves carbon from the air into wood, and holds it therethe phrase “grow to maturity” is doing real work – young trees store far less
WE 2
Explain why peat stores carbon
Explain why peat bogs act as carbon sinks, and how draining them releases carbon dioxide. (4 marks)
Point 1: the conditions
Peat bogs are waterlogged, and therefore anaerobic, and acidic.
Point 2: why that stores carbon
Decomposers cannot function properly in these conditions, so plant matter only partly decomposes and the carbon in it accumulates as peat.
Point 3: what draining does
Digging drainage ditches allows the peat to dry out, removing the waterlogged anaerobic conditions.
Point 4: the release
Decay organisms become active, decomposition proceeds, and respiration by these organisms releases carbon dioxide into the atmosphere.
Carbon is stored by decomposition failing, and released when it restartssay both “anaerobic” and “acidic” – one on its own usually only earns half the credit
WE 3
Evaluate two approaches
Outline the scientific debate over whether non-native plantations or rewilding with native species is the better approach to carbon sequestration. (3 marks)
Point 1: one position
Some scientists favour planting fast-growing non-native trees, because these sequester the maximum mass of carbon in the shortest time.
Point 2: the other position
Others favour rewilding, encouraging the growth of native species so that naturally occurring ecosystems are restored.
Point 3: the trade-off
Rewilding sequesters carbon more slowly, but is likely to be more beneficial for biodiversity.
Speed of carbon capture against ecosystem qualitypresent it as a genuine disagreement between scientists, not as one side being wrong
💡 Exam tips
Learn the definition of carbon sequestration as a single sentence.
Distinguish regeneration (replanting cleared land) from afforestation (new forest).
For peat, always give both conditions: waterlogged/anaerobic and acidic.
Mention that artificial storage is still at the research stage if asked about future options.
Use Costa Rica as a named example, including the government support needed.
In NOS questions, present both positions and name the trade-off.
⚠ Common mistakes
Saying peat forms because plants grow quickly. It forms because decomposition is incomplete.
Thinking a bog must be dug up to lose its carbon. Simply drying it out is enough.
Using regeneration and afforestation interchangeably. They describe different situations.
Claiming artificial carbon capture is already solving the problem. It is still being researched.
Writing that trees store carbon dioxide. They store carbon, as carbon compounds in biomass.
Treating the rewilding debate as settled. The syllabus point exists precisely because it is not.
Up next: Climate Change & Phenology – how warming knocks the timing of biological events out of step, and why a caterpillar peaking two weeks early is bad news for a nest full of chicks.
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