Your net zero target will one day require you to neutralise the emissions you cannot cut. Offers for that are already on the market: forest projects, soil carbon, biochar, carbon capture and storage. Each method stores carbon in a different place and for a different time. Not every one of them takes CO₂ out of the air.
- Carbon sequestration: capturing CO₂ and storing it for a long time in soil, plants, oceans, rocks or products.
- Methods: geological, biological, carbon farming, industrial carbon capture and storage (CCS) and chemical storage in minerals.
- Carbon removal: takes CO₂ out of the air; CCS at a chimney prevents emissions but is not a removal.
- Permanence: carbon in trees and soil can return to the air; carbon stored in rock stays for centuries.
What is carbon sequestration?
Carbon sequestration means that carbon dioxide (CO₂) is captured and stored. More carbon then stays in soil, oceans, plants or rocks. The CO₂ can come from the air, or from a factory before it gets out.
Greenhouse gases, such as CO₂, drive climate change. Warming harms nature, animals and people. Sequestration lowers the amount of CO₂ in the air, and so its effect on the climate. Natural carbon sinks, such as forests, soils and oceans, already store carbon. But they take up only part of what we emit.
What are the benefits of carbon sequestration?
Sequestration helps to limit the effect of greenhouse gases on the climate. Its benefits include:
- less CO₂ that warms the climate;
- more carbon stored in soil;
- better soil and better crops;
- the chance to use CO₂ to make chemicals and fuels;
- lower CO₂ costs for industry;
- better health for people and animals, thanks to lower emissions.
What methods of carbon sequestration and storage are there?
Sequestration happens both in nature and through human action. The methods differ in where the carbon goes and how it is held. The main ones are:
- geological sequestration;
- biological sequestration, including seaweed;
- carbon farming;
- carbon capture and storage from industry (CCS);
- chemical sequestration.
Geological carbon sequestration
In this method, CO₂ is stored deep underground. It is pumped into a chosen geological formation. This can be salty water deep in the rock, an empty oil or gas field or a coal seam that cannot be mined. Over time, part of the gas dissolves in the water or turns into minerals. This needs special equipment and long-term checks of the storage site.
Biological carbon sequestration
The biological method uses ways of farming that help plants take up more CO₂. Soil can store more carbon than it would on its own, above all in carbon farming. Cover crops, no ploughing and more organic matter in the soil can all raise carbon uptake.
Another new method uses seaweed. These sea plants take up CO₂ very well. Seaweed in the world's oceans may store about 173 million tonnes of carbon a year (Krause-Jensen and Duarte, 2016).
Carbon farming
Carbon farming means ways of growing food that store more carbon. Terms such as regenerative farming, agroforestry and carbon farming are often used as synonyms. They include no ploughing, crop rotation, cover crops and keeping animals on the land.
Many governments now see this kind of farming as part of the answer to climate change. They are writing rules for carbon farming. In the EU, Regulation (EU) 2024/3012 (CRCF) sets up certification for carbon farming and carbon removals.
Carbon capture and storage from industry
In industry, sequestration means carbon capture and storage (CCS). A plant captures CO₂ from a factory or a power station and sends it to a storage site.
CCS is often controversial. It is expensive, and critics say it can keep fossil fuel plants running longer instead of replacing them.
Chemical carbon sequestration
The last method is chemical. It uses a process called mineral carbonation. CO₂ reacts with rock or waste that contains calcium or magnesium. This forms solid carbonates that do not dissolve. In this way, carbon can be stored in building materials, such as cement.
Carbon removal
Carbon sequestration and carbon removal are related, but they are not the same. Carbon removal means taking CO₂ out of the air and storing it. It can be stored in plants, soils, oceans, rocks, caverns deep underground or long-lasting products such as cement.
Forests, carbon farming and seaweed farms count as carbon removal. So does direct air capture, which takes CO₂ straight from the air and stores it deep underground. Carbon capture and storage (CCS) at a factory does not count. There, carbon is caught at the source and never reaches the air. So CCS prevents an emission, but does not remove one.
How long the carbon stays stored also matters. Carbon in trees and soil can return to the air after a fire, logging or ploughing. Carbon stored in rock or turned into minerals stays there for centuries.
New technologies for capturing carbon from the air
Scientists and engineers are working on better ways to capture and store CO₂. For example, new materials that bind only CO₂ could make capture work better.
Seaweed farms, artificial photosynthesis and other new solutions may also store more carbon. They may also let us use the captured carbon, for example in building materials, fuels or fertilisers.
Carbon sequestration is an important part of the response to climate change. It works best together with emission cuts and sustainable business practices. Sequestration projects can also issue units for sale on the market. We describe carbon removal credits, their prices and how to judge their quality in a separate article.