Carbon Sequestration 101: Everything You Need to Know

Quick Key Facts

• Forests, grasslands and farms have traditionally captured about 25% of carbon emissions.
• Grasslands store about 12% of Earth’s terrestrial carbon.
• Each year, the planet’s peatlands store 307 megatons of carbon, more than the total carbon storage of all types of vegetation on Earth.
• The surface layer of the ocean has absorbed up to 30% of the carbon dioxide released by humans burning fossil fuels.
• Our planet’s forests, soils and oceans are its biggest carbon sinks.
• Most carbon on Earth is stored in sediments and rocks.
• Carbon is present in all living things on the planet.
• Humans are made up of about 18.5 percent carbon.

What Is ‘Carbon Sequestration’?

Carbon sequestration is the process of capturing atmospheric carbon dioxide — the most commonly produced greenhouse gas — and storing it in the Earth. Most of the carbon dioxide in the atmosphere is formed by the combustion of fossil fuels, primarily coal and petroleum.

The amount of atmospheric carbon dioxide has increased by 30% over the past 150 years. It is the general consensus of most scientists that there is a direct correlation between rising global temperatures and increasing carbon dioxide levels. The purpose of carbon sequestration is to reduce the amount of heat-trapping carbon dioxide in the atmosphere, in order to reduce global heating and climate change.

There are three types of carbon sequestration: biological, geological and technological. Biological carbon sequestration is the storage of carbon dioxide in vegetation found in the oceans, soils, forests and grasslands. Geological carbon sequestration is the process of storing carbon in underground geologic formations, like rocks. Technological carbon sequestration is a range of methods scientists are exploring to remove and sequester carbon using new technological innovations, as well as the investigation of innovative ways to use the carbon as a resource.

What Is the Carbon Cycle and Why Is It Important?

Carbon is a chemical element that is necessary for the formation of the DNA and proteins that make up all living things on Earth. Arthropods like insects, crustaceans and spiders are made up of about 50 percent carbon; on average mammals — both marine and terrestrial — are composed of about 8.35 percent carbon, and about 35 to 65 percent of the dry weight of biomass on Earth consists of carbon.

Earth’s carbon cycle keeps carbon — the amount of which never changes — continuously moving from the atmosphere back down to Earth where it is used, stored and released back into the atmosphere.

Carbon is found in the form of carbon dioxide in Earth’s atmosphere and helps to regulate our planet’s temperature. Without carbon dioxide and other greenhouse gases, our planet would be frozen, like Uranus and Neptune. With an excess of greenhouse gases, it would be too hot, like Venus. The carbon cycle keeps carbon moving to where it is needed on Earth, making sure our planet avoids these extremes.

Most of the carbon on Earth is stored in sediments and rocks, while the remainder is contained in the atmosphere, ocean and living things. These, along with environments like tropical rainforests, peatlands, grasslands, swamps, northern boreal forests, soils and coral reefs, are called carbon sinks — natural environments that have the ability to absorb carbon dioxide from the atmosphere and store it, sometimes for millennia. Carbon sinks absorb more carbon than they release, which means they lower the concentration of atmospheric carbon dioxide, helping to keep global warming in check.

Carbon can be rereleased into the atmosphere through the burning of fossil fuels — made up of prehistoric plants and animals that died and over time were embedded in layers of rock — the burning of biomass, the eruption of volcanoes and the death and decomposition of plant and animal matter and other processes.

The excess carbon dioxide that occurs when fossil fuels are burned by humans changes the planet’s climate, resulting in increased temperatures that lead to ocean acidification and disruptions to Earth’s delicately balanced ecosystems.

Why Is Carbon Sequestration Important?

Human & Climate Impacts

In less than 200 years, human activities have increased the carbon dioxide levels in the atmosphere by 50 percent. Around 45 percent of the carbon dioxide emitted by humans is still in the atmosphere, but carbon sequestration can prevent further emissions from contributing to global heating. Carbon sequestration reduces carbon dioxide levels in the atmosphere, which slows planetary warming and its negative effects on the climate. Global heating has led to an increase in wildfires, droughts, more extreme weather events, the melting of the polar ice caps and Arctic sea ice, sea level rise and other climate-related disasters.

Biodiversity Impacts

Experiments have found that increasing the abundance of plant species boosts carbon storage significantly. Grasslands have an important role in the planet’s carbon cycle. As atmospheric levels of carbon dioxide continue to rise, grasslands with more biodiversity can store more carbon.

Biodiversity enhances the storage of soil organic carbon (SOC) by increasing the diversity of soil microbes, improving net carbon gains — especially underground — and by subduing the losses of carbon from microbial decomposition.

Types of Carbon Sequestration

Biological Carbon Sequestration

Biological carbon sequestration occurs because of the natural ability of vegetation and ecosystems to store carbon. Plants capture atmospheric carbon and collect it as carbohydrates. Carbon can be stored in root systems, tree bark and trunks, leaves, branches and in seagrass beds through sedimentation. Carbon is stored in vegetation found in oceans, coastal wetlands, forests, grasslands, soils, peat marshes and arid regions like deserts. When plants die or their branches or leaves fall off, the carbon stored in them is either released into the atmosphere or absorbed into the soil or seabed.

Oceans & Coastal Wetlands

Phytoplankton, seagrass, algae and other ocean organisms like microscopic plants collect organic carbon and store it in the sediments on the ocean floor. Atmospheric carbon captured and stored by coastal wetlands ecosystems and oceans is referred to as blue carbon.

Parts of the ocean that are colder and rich in nutrients have the ability to absorb more carbon than warmer parts of the ocean. This is why the polar regions of the globe are generally carbon sinks.

It is thought that by the year 2100, much of the world’s ocean will be a carbon sink, which could change the chemistry of the ocean and reduce the water’s pH, causing it to become more acidic.

Forests

Forests absorb atmospheric carbon dioxide through photosynthesis and store it in both living and dead trees, their root systems, the forest floor itself, undergrowth and soils. Collectively, these carbon repositories are called carbon pools. The highest carbon density exists in live trees, soils and the forest floor.

Deforestation and wildfires can disrupt forest ecosystems and release sequestered carbon back into the atmosphere, thereby reducing forests’ effectiveness as carbon sinks.

Grasslands

About a quarter of Earth’s surface is covered by grasslands. These areas covered in herbaceous vegetation store about 12 percent of the planet’s terrestrial carbon, of which about 81 percent is stored in the soil.

Because most of the carbon absorbed by grasslands is stored underground, when there is wildfire or drought the sequestered carbon isn’t as susceptible to being disturbed and released back into the atmosphere. When the actual plants themselves are burned, the carbon they’ve stored remains safely in the roots and soil.

While forests have the potential to store more carbon than grasslands, grasslands are more resilient in the face of the unpredictable and often harsh conditions that come with climate change.

Peatlands

Peatlands consist of water and thick vegetation and play a critical part in carbon storage. Three percent of the planet’s surface is made up of peatlands. Damaged peatlands account for five percent of human-caused carbon emissions.

Types of peatlands include marshes, mudflats, estuaries, bogs and fens. Peat bogs sequester the most carbon of all types of peatlands. 

These important carbon stores can go as deep as 65 feet underground and can take thousands of years to form. These natural treasures are threatened by rising temperatures, wildfires and development. Since they take so long to develop, once they’re gone they are difficult to restore and their stored carbon gets released back into the atmosphere.

Oftentimes peatlands in tropical regions get converted to agricultural uses like palm oil production, which involves draining the wetlands, dramatically reducing their ability to store carbon. The process of converting these ecologically valuable lands in Indonesia and Malaysia is responsible for 30 percent of the countries’ overall greenhouse gas emissions.

A group of 380 mosses collectively referred to as sphagnum moss is always growing and replacing older moss in a healthy peat bog. These mosses depend on wet and cold conditions and, even as they die and turn into soil, their chemical components are retained and enrich the soil.

When the moss in a peat bog is broken down by fungi and bacteria, acid is released that stays in the surrounding water, which is already low in oxygen because the water doesn’t flow. The high acid, low oxygen conditions prevent dead moss from decomposing as new moss continues to grow and cover it. As the dead moss sinks into the bog, along with its organic compounds, the carbon remains stored within it instead of being released back into the atmosphere.

The peat — which contains most of the carbon in the bog — lies beneath the layers of dead moss and new sphagnum moss.

The carbon in peat bogs can take thousands of years to collect, and typically soil consisting of more than 20 to 30 percent organic matter is considered peat.

As temperatures rise twice as fast as the global average just below the Arctic Circle — where there is a concentration of peatlands — peatlands are drying out and creating ideal conditions for fires.

Soils

The main way carbon is stored in soils is as soil organic matter (SOM), which consists of different carbon compounds found in decomposing animal and plant tissue, fungi, bacteria, nematodes, protozoa and carbon from minerals in the soil.

As plants use photosynthesis to turn carbon into oxygen, carbon is stored as SOM, usually for several decades.

In desert and arid regions of the world, carbonates — formed by carbon dioxide dissolving in water and percolating in the soil over thousands of years — mix with magnesium and calcium, forming a mineral deposit called “caliche.” Carbonates have the ability to store carbon for more than 70,000 years.

Scientists have been adding pulverized silicates to soil in order to accelerate the formation of carbonates so that carbon can be stored for longer periods.

Geological Carbon Sequestration

Geological Carbon Sequestration is a type of carbon capture and storage (CCS) that stores carbon dioxide by injecting it into geologic formations, like porous rocks, in order to use the planet’s deep underground environment for long-term storage.

Types of geological carbon sequestration sites include coal beds, deep saline formations and former oil and gas reservoirs.

Technological Carbon Sequestration

Technological carbon sequestration is when scientists use innovative technologies — like CCS and carbon capture, utilization and storage (CCUS) to remove carbon from the atmosphere and store it. They are also exploring ways to use the sequestered carbon as a resource.

Carbon Capture & Storage

CCS is the process of capturing and storing carbon dioxide from the fossil fuels produced by human activities in order to prevent it from accumulating in Earth’s atmosphere.

The carbon is initially captured from an energy source where it is created — like a natural gas processing plant, power plant or oil refinery — or an industrial source, like a cement or steel factory.

Using CCS at an industrial facility or power plant usually involves capturing, transporting and storing the carbon. Different technologies are used to capture carbon dioxide at the emission point, but once the carbon dioxide is at a high enough concentration that it can be separated, compressed and chilled, it is captured and transported as a liquid via a pipeline to a special site where it is injected and sequestered.

Ships, pipelines and sometimes vehicles or trains are used to bring the liquified carbon to a suitable storage location. The carbon is then injected into the geological formations underground for long-term storage.

Carbon Capture, Utilization & Storage

When carbon dioxide is captured from emissions from a factory smokestack or other source — such as the air that surrounds us — it can be used to make a range of products, from concrete and plastics to fuel for vehicles and aircraft, even carbonated drinks.

This process — trapping carbon and making materials out of it — is called CCUS. While the technology is there, how the public would feel about drinking a beverage made with recycled carbon dioxide is something that’s still being discussed and explored.

Employing CCUS could put billions of tons of carbon to practical use in a wide array of sectors, rather than releasing it back into the atmosphere.

Graphene Production

Another example of carbon being recycled and turned into a material resource is graphene production. Graphene is a material used to make smartphone screens and other technological instruments. At temperatures of as much as 1,832 degrees Fahrenheit, carbon and hydrogen can be converted into graphene.

Direct Air Capture

Direct air capture (DAC) uses chemical reactions from engineered molecules that are designed to attract and pull carbon dioxide directly from the air. The most advanced systems use ordinary chemicals in the form of solvents or sorbents that single out carbon dioxide and trap it as the air moves over them. These carbon-trapping chemicals can then be reused.

As with carbon capture, carbon trapped using DAC can be injected into underground geologic formations or used in materials or products. When used in making materials like plastic or concrete, the carbon can be sequestered for decades or centuries. If it’s used in the making of fuel or beverages, it wouldn’t be long before it was released back into the atmosphere — not the most climate-friendly application. However, in the case of fossil jet fuel, it could still be a better alternative.

Benefits of Carbon Sequestration

Part of Earth’s natural carbon cycle, carbon sequestration is an important component of our planet’s overall balancing act.

Biological carbon sequestration is the most plentiful and reliable way to remove carbon dioxide from the air, but technological methods like CCS and CCUS can also be utilized to offset the additional greenhouse gas emissions from human activities. The best way to keep harmful emissions in check, however, is to reduce and eventually eliminate the use of fossil fuels.

In addition to removing carbon dioxide from Earth’s atmosphere — which helps slow down global heating — other benefits of carbon sequestration include improved soil health, which means better climate resilience and a reduced need for synthetic fertilizers.

Improved Soil Health

Higher SOC improves soil health by increasing the physical stability and structure of the soil, which improves water retention, drainage and aeration, as well as reduces the risk of nutrient loss and erosion.

Increased SOC also helps restore degraded soils, which means better agricultural productivity.

There are various ways to increase SOC, which fall under the general umbrella of regenerative agriculture. These include reducing soil disturbance through the use of low- or no-till farming practices, planting perennial crops, crop rotation, the application of crop residue or compost and managed livestock grazing.

Better Climate Resilience of Soils

Healthy soils are important because they not only have the ability to store more carbon, but can also absorb and hold a greater volume of water, making them more drought-resilient.

The ability of healthy soils to absorb more water before becoming saturated also means greater flood resilience and a reduction in cropland runoff.

Reduced Need for Fertilizer

Healthier soils don’t need as much or even any fertilizer to be productive, as they already have an adequate balance of the nutrients needed for plant growth. Using less fertilizer is better for the environment and can save farmers money.

Excessive fertilizer use can cause salt concentrations that are too high and can harm good soil microorganisms. Too much fertilizer is bad for ecosystems, as the excess nutrients can get swept into freshwater systems and create dangerous algal blooms.

Synthetic fertilizers that have been broken down by soil microbes can also release nitrous oxide — a powerful greenhouse gas.

Challenges of Carbon Sequestration

Saturation

New soil is made when carbon and microbes are added to existing soil from decomposing plant matter, fungi, plant roots and livestock manure.

While the shallower parts of healthy soils can become temporarily saturated with carbon, the carbon-saturated soil is continuously recycled and incorporated into the existing soil to make new soil with the capacity to hold additional carbon.

Reversibility

Carbon can be rereleased into the atmosphere through a variety of mechanisms, including human activities like the burning of biomass and fossil fuels, wildfires and the disturbance of soils.

It is important to maintain soil management practices that focus on soil health rather than increasing crop yields through the use of synthetic fertilizers — which do not contain soil-building nutrients — and monoculture, which disrupts soils’ natural balance. Healthy soils mean nutrient-rich foods, productive harvests and an essential repository for sequestered carbon.

Measurement

It is difficult to calculate the amount of carbon that has been removed from the atmosphere and sequestered in Earth’s oceans, rocks, trees and soils because there are many different variables involved in the complex processes of biological carbon sequestration.

Currently, monitoring and verifying the removal of carbon is too costly and difficult to try and implement on a large scale.

Pollution

Underground reservoirs used in CCS have the potential to leak carbon back into the atmosphere or groundwater. They can also bring about induced seismicity — human-caused tremors and earthquakes caused by changes in the pressure and strain on Earth’s crust.

Energy Intensive & Costly

DAC is energy intensive and still too expensive to implement on a mass scale, but it provides permanent and measurable carbon storage.

Because of the enormous energy requirements needed for the isolation of carbon dioxide from the ambient air, DAC is more expensive per ton of carbon removed from the atmosphere than many natural carbon removal methods or mitigation strategies.

There are varying estimates for the costs of DAC, but one estimate from 2022 says that they range from $250 to $600 per metric ton of carbon removed. By contrast, the cost of most reforestation is less than $50 per metric ton. In the next five to ten years, DAC costs could go down to $150 to $200.

The Carbon Negative Shot initiative launched by the Department of Energy in 2021 has a goal of reducing the costs of gigaton-scale technologies for carbon removal to $100 per ton.

One of the reasons DAC is so expensive is that there aren’t as many projects or companies using the method, but if that changes costs could come down.

What Can We Do to Support Carbon Sequestration?

As a Society?

The best way to support carbon capture is to preserve forests, wetlands, peatlands and their ecosystems, while reclaiming agricultural land to be reforested and rewilded.

Reducing the use of plastics and other toxic pollutants and preventing them from reaching our oceans, lakes and waterways will help nurture the best environments for carbon capture in our planet’s waters.

Improving land management methods and promoting regenerative agriculture while phasing out industrial agriculture will increase the ability of soils to absorb and sequester carbon.

In Our Own Lives?

Planting a garden, trees and flowers without the use of synthetic fertilizers or toxic pesticides, rewilding our own green spaces and adopting practices that help naturally regenerate soil are all ways to contribute individually to the lowering of carbon dioxide in our atmosphere.

In addition, anything we can do to reduce the production of fossil fuels — lowering our electricity use, reducing or eliminating meat and dairy from our diets, shopping and eating locally, avoiding fast fashion, minimizing the use of plastics and plastic packaging, traveling as efficiently as possible, utilizing solar, wind and other forms of renewable energy and driving electric rather than gas-powered vehicles — means less carbon dioxide is released into the atmosphere that will need to be captured and stored.

Takeaway

Carbon sequestration is an essential part of Earth’s carbon cycle and the maintenance of the balance between carbon coming together with other elements to make life and its natural release back into the planet’s atmosphere.

The Paris Agreement goal of limiting global heating to well below two degrees Celsius — preferably 1.5 degrees Celsius — above pre-industrial levels is one of the main ways humans are attempting to mitigate climate change and all of its disastrous consequences. In order to meet that target, the burning of fossil fuels must ultimately cease.

In the interim before the transition to 100 percent renewable energy — which will hopefully occur by 2050 at the latest — humans must do all we can to limit the release of carbon dioxide into the atmosphere.

To that end, technologies like CCS and CCUS may be utilized alongside reductions in the use of fossil fuels, factory farming — which produces a large amount of methane and nitrous oxide — and the destruction of forests for agriculture.