What are Carbon Sinks? Different Types and Their Importance 

We can’t discuss carbon sinks without addressing carbon sequestration- the long-term storage of carbon dioxide in plants, soils, oceans, and other geological formations. A carbon sink is a natural ecosystem that removes carbon dioxide from the earth’s atmosphere. 

Human activities and industrialization advancements are among the primary carbon sources on the earth’s surface. Carbon sinks help mitigate the harmful accumulation of carbon emitted.  

This article explains artificial and natural carbon sinks. It also discusses the various types of carbon sinks and their importance. 

Table of Contents:

What are carbon sinks?

Carbon sinks refer to any natural ecosystem or artificial technologies that absorb carbon dioxide from the atmosphere and offset carbon emissions. They maintain the concentration of carbon dioxide in the atmosphere, reducing the risks of climate change and global warming. 

Types of carbon sinks

Natural Carbon Sink   

As you can already identify from the name, natural carbon sinks refer to a natural ecosystem on the earth’s surface that absorbs and stores carbon. Earth’s natural carbon sinks are: 

1. Forests 

Forest ecosystems are among the most prominent natural carbon sinks. Climate researchers consider a forest ecosystem a carbon sink when it captures more carbon than it releases. Trees play a significant role in capturing carbon dioxide in forests, and we can trace this back to the carbon cycle. 

The carbon cycle is a process by which the earth recycles carbon and ensures it reaches the living organisms that need it. Trees and vegetation are part of the carbon cycle, which is necessary for thriving plant growth. 

Trees absorb carbon from the atmosphere during photosynthesis, convert it to sugar or glucose, and release oxygen back into the atmosphere. They also use organic carbon to grow roots, branches, leaves, and seeds. Trees make incredible natural carbon sinks because about 50% of wood is carbon.

They keep absorbing more carbon dioxide because there is no limit to the quantity a tree can absorb. Forests also make the perfect carbon sink because the stored carbon lasts as long as the trees stand. It takes years to release the carbon stored, with some exceptions. 

Trees and vegetation release trapped carbon when their roots burn sugar to get water and other nutrients or when plants die and decompose as organic matter does. Forests store carbon at varying amounts and speeds, depending on the age and number of trees. New/young forests have many trees that multiply, enabling efficient carbon sequestration.

As forests age, their carbon storage potential increases. The mature and old-growth forests hold significant carbon despite their slower growth rate. Even when older trees die, the new ones compensate for this loss by absorbing carbon during their growth. However, newer forests sequester carbon more swiftly.

Related Read: What Is Sustainable Forestry?

2. Soil 

Carbon sequestration and soil go hand in hand. It is the second-largest natural carbon sink. Atmospheric carbon becomes soil organic carbon when plants photosynthesize, converting carbon compounds through the plant roots and residues. 

Soil also stores carbon through the decay of dead plants, animals, and microorganisms. Carbon content in soil is necessary because it helps improve soil structure and fauna. It also improves soil fertility and nutrient and water retention capacity.

A 1% increase in soil organic carbon can improve soil water retention capacity by 20,000 gallons per acre. Grassland soil can absorb up to 6.5 billion metric tons of carbon yearly¹, while croplands store up to 1.85 billion tons yearly³.

Changes in land use can affect soil’s carbon sequestration abilities. However, an increase in soil organic matter will ensure the continued storage of carbon. Organic matter helps increase the amount of carbon soil can absorb. The soil can store carbon for a long time, centuries even, but only if left undisturbed. 

However, soil degradation releases stored carbon back into the atmosphere. It is how we lost some of the world’s original soil carbon stock. Using land for human practices like agriculture and the Industrial Revolution reduces soils' ability to sequester carbon. The increase in land use over the past 12,000 years caused the loss of 133 billion metric tons of carbon from the soil⁵.

Related Read: Role of Soil Health in Climate Change Mitigation.

3. Oceans 

Earth’s oceans are the largest carbon sink on earth. It absorbs 25% of the carbon emissions and 90% of the excess heat from these emissions. So, how does the ocean absorb carbon from the atmosphere? 

The ocean covers 70% of land and has an ecosystem. It is the largest ecosystem on earth because we haven't explored up to 10% of the deep ocean. Mangroves, tidal marshes, and seagrass meadows store carbon—often called "blue carbon"—deep within their organic-rich soils. 

Despite covering only 0.2% of the ocean's surface, mangroves greatly contribute to organic carbon storage. Mangroves particularly shine, storing significantly more carbon within their biomass and soils. They can also store up to five times the amount of carbon as tropical forests on land⁴.

Plant-like phytoplankton consumes the carbon on the ocean’s surface, and other aquatic animals eat the plant-like phytoplankton. Eventually, they all die, and bacteria feed on them as they decay. This natural process produces C02, which dissolves at the bottom of the ocean. 

However, the ocean is not a reliable carbon pool. Carbon absorption changes the ocean’s chemistry by increasing its acidity, causing ocean acidification. The ocean’s acidity is steadily rising because of increased atmospheric carbon, causing problems for its organisms. 

Ocean acidification creates climatic conditions that destroy the minerals coral reefs, shrimp, clams, and oysters use to build skeletons and shells. It also fosters rapid algal blooms, which are harmful to human health. 

We can reduce the rate of ocean acidification by dissolving specific rocks like Olivine, a magnesium silicate mineral. However, it is not advisable because it contains metal that can harm aquatic organisms. Reducing emissions is the best way to keep the ocean’s carbon sequestration efficiency.

4. Fungi  

There’s a vast carbon pool in the earth’s crust. The pool is mycorrhizal fungi, a network of fungi beneath natural and urban environments. Scientists and researchers from the University of Sheffield recently discovered the extent to which mycorrhizal fungi can capture carbon⁶.

Initially, they believed mycorrhizal fungi could store carbon through their symbiotic relationship with terrestrial plants. The plant with which they form a relationship converts the absorbed sugar into sugar and fat, transferring it into the soil. The fungi have been supporting the terrestrial ecosystem for over 450 million years. 

The discovery shows that fungi store over a third of the carbon emissions from fossil fuels. Mycorrhizal fungi receive a transfer of 13.2 gigatons of carbon from plants annually, making it the soil’s most significant carbon source. Mycorrhizal fungi should be part of the essential carbon sinks because they are partially responsible for the carbon sequestration of forests and soils. It enhances their ability to keep carbon trapped.

However, this potentially huge carbon pool faces problems of its own. Research shows some forests in the United States have fewer trees with fungi because of another one of the greenhouse gases, nitrogen. Reducing nitrogen pollution in the environment will help restore the fungi and increase the sequestration process of the various ecosystems².

Artificial Carbon Sinks  

Artificial carbon sinks use technology to capture carbon from the atmosphere, store it somewhere, or recycle it. We discovered artificial carbon sequestration methods because we don’t want to stop the activities producing harmful emissions. 

An example of an artificial carbon sequestration process is ocean sequestration. It involves injecting carbon into the deepest depths of the ocean to form lakes of CO2. Scientists believe the oceans' pressure and temperature will keep the carbon down⁷.

Another technological innovation to capture carbon is Direct Air Capture (DAC) technologies. DAC removes CO2 from the atmosphere at any location and stores it in deep geological formations or recycles it. There are 27 DAC plants worldwide, and 130 more plants are in different construction stages. The 27 plants capture 0.01 Mt of carbon annually.

According to the Department of Energy, direct air capture is expensive, and governments are looking to reduce the costs to make carbon capture easier. These technologies operate using liquid solvents and solid sorbents.

Liquid solvents pass air through chemicals to remove CO2. Some existing systems use heat and vacuum to remove the captured carbon and return the chemicals to the air. Solid sorbents, on the other hand, use physical filters that chemically bind carbon molecules. Then, the filters heat or pass through a vacuum, releasing carbon into reservoirs or reuse.

Importance of carbon sinks

Climate Change Mitigation 

The availability of carbon sinks ensures the natural or artificial process of capturing carbon dioxide from the atmosphere. Carbon sinks are essential because they help mitigate climate change. 

We have natural carbon stock, a part of the carbon cycle necessary for survival. We also have carbon sources from using carbon pools. A carbon pool is a reservoir of carbon dioxide that can absorb and release natural gas. Some examples of carbon pools are the earth’s crust, oceans, forests, and sedimentary rocks.  

We release carbon through our interaction with these carbon sinks. For instance, burning fossil fuels can power industrial revolutions and the manufacturing industry. The extraction of fossil fuels contributes to carbon emissions, and the use of fossil fuels for various products and services causes fumes and plastic pollution, contributing to climate change and global warming. 

Natural carbon sinks help us mitigate the effects of global warming by absorbing the carbon emitted. Currently, the world is experiencing severe climate change. There is an influx of extreme weather conditions like; 

1. heat waves in India, 
2. flooding and landslides in Brazil, 
3. tornadoes in the United States, 
4. freezing in Afghanistan, 
5. flooding in South Korea,
6. wildfires in Canada, and 
7. Hawaiian fires.

Increasing the capacity of Earth’s carbon sinks will help us combat climate change. It will also stop ocean acidification and forest desertification. 

Protect and Nourish The Ecosystem and Its Organisms

Apart from carbon capture, carbon sinks help the earth’s ecosystems flourish. The natural process of trees and soil absorbing carbon helps purify the air and water. Using carbon to photosynthesize provides us with cleaner air and oxygen. 

Actively sequestering carbon on agricultural land also improves soil health and, by extension, leads to a bountiful harvest. It protects the resources wildlife and humans rely on for survival and fosters an abundance of wildlife. 

Conclusion  

Carbon sequestration helps reduce the risk of climate change. However, the environmental impacts of our activities, such as intensive farming practices and fossil fuel burning, damage natural carbon sinks. 

To mitigate the climate crisis we are experiencing, we need to focus on ecosystem restoration and reduce our contribution to carbon emissions. For instance, we should stop deforestation and burning trees because these activities release carbon dioxide back into the atmosphere.