The obvious response to too much carbon dioxide in the air is to take some out. Engineering a machine to do that is still largely at the research stage — but forests, peat bogs and oceans have been doing it for millions of years for free. Carbon sequestration is mostly about not breaking those, and repairing the ones already broken.
📘 What you need to know
Carbon sequestration is the process of capturing and storing carbon dioxide from the atmosphere.
It is achieved by increasing the removal of carbon into natural carbon sinks; artificial storage is still at the research stage.
Forest regeneration (reforestation) means planting trees in deforested areas; afforestation means creating new forest.
Trees grown to maturity store large amounts of carbon in their biomass.
Peat bogs form where plant matter cannot decompose fully because conditions are waterlogged (anaerobic) and acidic.
Peat bogs are restored by filling in drainage ditches and regulating peat harvesting.
There is active scientific debate over whether fast-growing non-native plantations or rewilding with native species is the better approach.
What sequestration means
Definition to learnCarbon sequestration = the process of capturing and storing carbon dioxide from the atmosphere
Scientists believe global warming can be slowed by increasing carbon sequestration. In practice this means increasing the removal of carbon from the atmosphere into natural carbon sinks. It is hoped that artificial carbon storage will become viable at some point, but that work is still at the research stage — which is why the biology syllabus focuses on the natural routes.
Every green arrow has a red one beside it. That symmetry is the reason conservation of existing sinks appears in sequestration answers as often as planting does.
Forest regeneration and afforestation
The two words are not interchangeable, and questions do test the difference:
Forest regeneration, also called reforestation, means planting new trees in deforested areas — putting forest back where it used to be.
Afforestation means the creation of new forests in places that were not previously forested.
If trees are allowed to grow to maturity, they store huge amounts of carbon in their biomass. The word “maturity” is doing real work there: a sapling planted and then felled for timber a few years later has sequestered very little.
Some countries have shown that restoring lost forest is genuinely possible. Costa Rica now plants around seven times more trees than it cuts down. Achievements on that scale require substantial government input, usually in the form of benefits paid to landowners — which is a reminder that this is an economic problem as much as a biological one.
Peat bog restoration
Peat bogs form where plant matter cannot decompose fully, because conditions are waterlogged — and therefore anaerobic — and acidic. Carbon stays locked in that partially decomposed plant matter, which makes peat bogs an essential carbon sink. Peatlands form in boreal and temperate ecosystems, and can form rapidly in tropical ones.
Two human activities damage them. Harvesting peat for fuel removes the store directly, and draining peat bogs to clear land for development or agriculture dries them out. Both release carbon back to the atmosphere — by combustion in the first case and decomposition in the second. Bogs are drained by digging drainage ditches to let the land dry out, and as the peat dries the activity of decay organisms increases.
The restoration is beautifully simple: fill in the drainage ditches and regulate peat harvesting. That allows the bog to recover and to continue growing in depth, which increases its ability to sequester carbon.
Peat bog restoration is one of the cheapest interventions in this whole unit. Blocking a ditch costs very little and switches a carbon source back into a carbon sink.
Link this back to the requirements for a stable ecosystem. Decomposers need oxygen, moisture and a suitable temperature. A waterlogged bog denies them oxygen, so decomposition stalls and carbon accumulates. Drain it and you hand the oxygen back.
NOS: an argument scientists are still having
Scientists do not always agree on the best approach to a problem, and different approaches bring different benefits and problems. Carbon sequestration by planting trees is a live example.
Approach
The argument for it
The trade-off
Plantations of fast-growing non-native trees
They grow quickly and sequester the maximum mass of carbon in the shortest time, which matters if the aim is to slow warming fast
A single-species plantation of non-native trees supports far less native wildlife than a natural woodland
Rewilding with native species
Encouraging the growth of native species restores naturally occurring ecosystems, which could be more beneficial for biodiversity
Carbon is sequestered more slowly, so less is removed in the short term
Notice that neither side is wrong about the biology. They are weighing two different goals — speed of carbon capture against biodiversity value — and which matters more is not a question that data alone can settle. That is exactly the point the NOS statement is making.
Worked examples
WORKED EXAMPLE 1
Explain how draining a peat bog changes it from a carbon sink into a carbon source. [4]
Step 1: why an intact bog stores carbon
Waterlogged conditions are anaerobic and acidic, so plant matter cannot decompose fully and carbon stays locked in the partly decomposed peat.
Step 2: what draining does
Drainage ditches let the land dry out, so oxygen reaches the peat.
Step 3: the biological consequence
Decay organisms become active, and their respiration releases carbon dioxide into the atmosphere.
Step 4: the outcomeRelease now exceeds storage, so the bog becomes a carbon sourcethe key word is anaerobic — it is the absence of oxygen that was doing the storing
WORKED EXAMPLE 2
Distinguish between reforestation and afforestation, and explain why trees must reach maturity to be effective for sequestration. [3]
Reforestation
Planting new trees in areas that were previously deforested.
Afforestation
Creating new forest in areas that were not previously forested.
Why maturity mattersCarbon is stored in the tree’s biomass, and biomass keeps accumulating as the tree grows, so a mature tree holds far more carbon than a young oneif trees are felled young, most of that stored carbon returns to the atmosphere quickly
WORKED EXAMPLE 3
A government must choose between planting a fast-growing non-native plantation and rewilding an area with native species. Discuss the advantages of each option. [4]
Case for the plantation
Non-native species chosen for fast growth sequester the maximum mass of carbon in the shortest time, which matters if warming must be slowed quickly.
Case for rewilding
Encouraging native species restores a naturally occurring ecosystem, so it is likely to support far greater biodiversity.
The trade-off
Rewilding sequesters carbon more slowly, while a plantation stores carbon fast but supports fewer native species.
A judgementThe best choice depends on whether the priority is rapid carbon capture or long-term biodiversity — scientists genuinely disagree on this“discuss” wants both sides plus a reasoned position, not a single preferred answer
💡 Exam tip
Learn the definition word for word: capturing and storing carbon dioxide from the atmosphere.
Keep reforestation and afforestation separate — the difference is whether forest was there before.
Explain peat bogs through anaerobic and acidic conditions preventing decomposition.
Say trees must reach maturity, and that carbon is stored in biomass.
Mention that artificial carbon storage exists but is still at the research stage.
For the NOS debate, give both positions and name the trade-off explicitly.
⚠ Common mix-up
Swapping reforestation and afforestation. Re- means putting it back where it was.
Saying peat forms because the ground is cold. The cause is waterlogging and acidity, which stop decomposition.
Thinking any planted tree sequesters well. It has to be allowed to grow to maturity.
Treating a carbon sink as permanent. Damage it and it becomes a source of the carbon it was holding.
Assuming the non-native plantation position is simply wrong. It has a real argument behind it; the debate is about priorities.
Confusing sequestration with reducing emissions. One removes carbon already in the air; the other stops adding more.
That completes Climate Change. The three pages fit together as cause, consequence and response — and the response page is the only one where the biology is genuinely on our side.
Want this explained one-to-one?
Book a free session with an experienced IB Biology tutor and get your trickiest topics made simple.
