Carbon sequestration at Higher Level: The same ideas as SL, with different examples: Iceland's Carbfix and Orca, Mediterranean seagrass and Canada's Quest. At HL, expect to weigh how secure and how large each kind of store is.
Practise this as you read
- Name the solid or liquid form for every store.
- Weigh artificial sequestration: what it stores against what it lets us keep burning.
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Catch it and lock it away: carbon sequestration takes carbon dioxide out of the atmosphere, or stops it getting there, and stores it as a solid or a liquid.
The points to remember
- Carbon sequestration captures CO₂ gas, from the atmosphere or from a chimney.
- It stores the carbon in a solid or liquid form, so it stays out of the air.
- It can be natural (plants, soils, oceans) or artificial (carbon capture and storage).
- The longer the carbon stays locked away, the better it is for the climate.
Remember it as: Catch the gas, lock it up as a solid or liquid.
Real example: at the Carbfix site in Iceland, CO₂ is dissolved in water (a liquid) and pumped into basalt. Within about two years most of it has turned into solid carbonate rock.
Say both halves: A definition needs the capture of the CO₂ gas AND its storage as a solid or liquid. 'Storing carbon' alone is too vague.
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Nature has sequestered carbon for billions of years. Living things build carbon into their bodies, and some of it is buried before it can rot.
The points to remember
- Trees absorb CO₂ by photosynthesis and turn it into biomass: wood, roots, leaves.
- Dead plant matter builds up in soils and peat where it decomposes slowly.
- In the sea, seagrass, kelp and plankton take up CO₂; some carbon sinks into the sediment.
- Over millions of years, buried organic matter is fossilised into coal, oil and natural gas.
| Natural store | How the carbon gets there | Form |
|---|---|---|
| Trees | Photosynthesis builds wood and roots | Solid biomass |
| Soils and peat | Dead leaves and roots rot slowly | Solid organic matter |
| Seagrass and sea floor | Plants and plankton sink and are buried | Solid sediment |
| Coal, oil and gas | Buried remains fossilised over millions of years | Solid, liquid, gas |
Real example: Posidonia meadows build thick mats of roots and sediment, several metres deep in places. The carbon in them has been stored for thousands of years.
Fossil fuels count too: Coal, oil and gas are carbon that plants and plankton sequestered long ago. Burning them undoes that sequestration in a few seconds.
People now copy nature with carbon capture and storage, often shortened to CCS.
How it works, step by step
- Capture: CO₂ is removed from the waste gas of a power station or factory.
- Compress: the CO₂ is squeezed into a liquid, so it can be piped or shipped.
- Store: it is pumped over 1 km down into salty sandstone, old oil or gas fields, or coal seams.
- An impermeable cap rock above stops it escaping; in basalt it can turn into solid rock.
- Direct air capture filters CO₂ straight out of the air, then stores it the same way.
Real example: since 2015 the Quest project in Alberta, Canada, has stored about 1 million tonnes of CO₂ a year from an oil plant. The Orca machine in Iceland, built by a Swiss company to take up to 4,000 tonnes a year straight from the air, shows direct air capture is still tiny.
Reading a CCS diagram: Follow each numbered flow: where the CO₂ comes from, which rock layer it goes into, and what (if anything) comes back up, such as oil or methane.
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Artificial sequestration can help, but it is not a simple fix. Weigh it up with points for and against.
For and against
- For: it removes CO₂ from the biggest sources before it reaches the air.
- For: it lets countries keep using fossil fuels while they switch to cleaner energy.
- Against: CO₂ pumped into an oil field pushes out more oil, which releases more CO₂ when burned.
- Against: it is costly and uses extra energy; a power station burns more fuel to run it.
- Against: it is small: about 50 million tonnes a year, far under 1% of the CO₂ we emit.
- Against: it treats the symptom; it does not cut the burning of fossil fuels.
Remember it as: Stores the waste, but can pump out more oil.
Real example: Petra Nova in Texas captured CO₂ from a coal power station and sold it to push more oil out of an old oil field. It shut down in 2020 when oil prices fell, showing that storage depended on oil sales.
The oil-field trap: CO₂ pumped into an oil field is stored, but the extra oil it pushes out is burned. Say both halves: some carbon is stored, yet more fossil carbon is released.
How this comes up: Paper 2, Section B (a): outline natural and artificial ways of sequestering carbon [4].
Countries are looking for ways to take carbon dioxide out of the atmosphere and keep it out.
Outline two natural and two artificial ways in which carbon can be sequestered.
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