There are only two ways to bring the carbon cycle back towards balance: put less carbon into the atmosphere, or take more out. Every strategy in this topic is one of those two, and answers get much sharper once you sort them that way instead of memorising a list.
📘 What you need to know
Human activity has raised atmospheric carbon dioxide and driven climate change.
Strategies either reduce sources or strengthen sinks.
Biomass and BECCS: energy from crops, with the emissions captured and stored underground.
Soil and forests: less tillage, less deforestation, reforestation of degraded land.
Artificial sequestration: carbon capture and storage from industry and power stations.
Ocean methods: fertilisation and increased upwelling to boost phytoplankton growth.
Two levers, that is all
Some measures sit in both columns. Protecting wetlands stops carbon being released and keeps a sink working, which is why it comes up so often.
Reducing the sources
Low-carbon technologies
Energy production, transport, industry and heating are the big emitters. Switching them to solar, wind and hydropower cuts emissions at the point where they are largest. Efficiency counts too — better insulation and heat pumps mean the same comfort for less fuel burned.
Burning fewer fossil fuels
This sounds like the same point, and it overlaps, but it is worth stating separately because it is the direct one: every tonne of coal, oil or gas left in the ground is carbon that stays in a long-term store.
Less soil disruption
Ploughing exposes soil organic matter to oxygen, so it decomposes and releases carbon dioxide. Crop rotation, cover cropping and reduced tillage keep that carbon where it is and cut erosion at the same time.
Notice how often the same practice appears in more than one topic. No-till farming turns up here, in soil systems, and in food production. Learning it properly once pays off three times.
Strengthening the sinks
Reforestation and reduced deforestation
Planting trees on cleared or degraded land sequesters carbon dioxide into biomass and soil. Preventing clearance in the first place is cheaper and faster, which is why international programmes such as UN-REDD focus on halting deforestation and promoting sustainable forest management.
Biomass and BECCS
Bioenergy crops absorb carbon dioxide as they grow, so burning them releases carbon that was recently taken from the air rather than fossil carbon. On its own that is roughly neutral. BECCS goes further: the carbon dioxide from burning the biomass is captured and stored underground, so the overall process removes carbon from the atmosphere.
Why BECCS gets attention. Most measures slow the rise. BECCS is one of the few that can produce a net removal — the crop takes carbon out of the air, and the carbon dioxide from burning it never gets back. The catch is that the crops need land that could be growing food or holding forest.
Artificial sequestration
Carbon capture and storage (CCS) traps carbon dioxide from industrial processes and power stations before it reaches the atmosphere, then transports it and injects it underground for long-term storage. It treats the emission at the chimney rather than avoiding it altogether.
Boosting ocean uptake
Two proposed methods both work by growing more phytoplankton, which photosynthesise and take up carbon dioxide:
Ocean fertilisation — adding nutrients such as nitrogen, phosphorus or iron to stimulate growth.
Increasing upwelling — bringing nutrient-rich deep water to the surface to do the same thing naturally.
Both are experimental, and both carry real risk of disrupting marine food webs, so treat them as proposals rather than solutions.
🧩 Structuring an “evaluate this strategy” answer
Say what it does. Reduces a source, or strengthens a sink.
Give the mechanism. How exactly does carbon stop entering, or start leaving, the atmosphere?
Give one strength. Scale, cost, speed, or a co-benefit such as biodiversity.
Give one limitation. Land needed, energy needed, cost, uncertainty, or unintended effects.
Reach a judgement. Say clearly whether you think it is worth doing and why.
WORKED EXAMPLE
Explain how reforestation reduces atmospheric carbon dioxide, and give one limitation of relying on it.
Step 1: Name the mechanismTrees absorb carbon dioxide during photosynthesisStep 2: Say where the carbon ends upstored in woody biomass and in surrounding soilsStep 3: Give the limitationTrees take decades to mature, and the carbon is released again if the forest burns or is clearedA real sink, but slow and not permanent
WORKED EXAMPLE
A power station switches from coal to biomass with carbon capture and storage. Explain why this can result in a net removal of carbon dioxide from the atmosphere.
Step 1: The growing stagebioenergy crops absorb CO2 as they photosynthesiseStep 2: The burning stageBurning would normally return that carbon to the airStep 3: The capture stagethe CO2 is captured and injected underground insteadCarbon comes out of the air and does not go back – a net removalOnly true if the crops are grown without causing deforestation
💡 Exam tip
Open by classifying: source reduction or sink enhancement. It shows the examiner you understand the cycle.
Always give a mechanism, not just a name. “Trees photosynthesise and store carbon in wood” beats “trees help”.
Learn two or three named examples properly (BECCS, CCS, UN-REDD) rather than eight vaguely.
Evaluate questions need a limitation as well as a benefit — land use, cost and permanence are safe ones.
Say what the strategy does to the balance of inputs and outputs. That is the language of the whole sub-topic.
⚠ Common mix-up
Treating burning biomass as automatically carbon negative. Without capture it is roughly neutral, not a removal.
Confusing CCS with BECCS. CCS captures emissions from industry; BECCS combines capture with bioenergy crops.
Saying renewables “have no carbon”. They emit far less in use, but manufacturing and installation still have a footprint.
Presenting ocean fertilisation as proven. It is experimental and could disrupt marine food webs.
Listing measures with no mechanism. A list scores far less than two well-explained examples.
Up next: Where Carbon Is Stored (HL) — the lithosphere and biological stores in detail, including limestone and methane.
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