What Are Carbon Sinks? How Do They Impact Climate Change?

A carbon sink is any natural system that absorbs and stores more carbon from the atmosphere than it releases. The largest carbon sinks on Earth are forests, soil, and the ocean, with the latter already accumulating roughly 30% of the atmosphere's total carbon dioxide emissions.

Why are they so important? Carbon dioxide (CO2) is released through natural processes, like when animals breathe and during volcanic eruptions, and human activities, such as burning fossil fuels and chopping down trees. Carbon sinks are nature's way of closing the gap between what carbon is released and what is stored. 

Carbon dioxide is also the main greenhouse gas responsible for climate change. As CO2 envelops the planet in greenhouse gas molecules and traps the sun's heat, it causes the global temperature to rise. Higher levels of carbon emissions mean more elevated temperatures. Since human activities produce increasingly more CO2 than the natural carbon storage process can handle, it is vital that nature's carbon sinks remain protected.

Types of Carbon Sinks

The world’s main carbon sinks are soil, plants, and the ocean. Together, these environmental powerhouses naturally accumulate carbon from the atmosphere and store it for long periods of time.

Soil

Soils contain mineral particles, broken-down plant matter, air, water, and even living organisms. This means they retain a large amount of carbon that those materials, predominantly plants, have taken from the atmosphere previously. Soils can store this carbon, which would have otherwise returned to the atmosphere as carbon dioxide, for a very long time.

Peatlands are wetlands where waterlogged conditions slow down plant decomposition to create carbon-rich soil, or "peat," in abundance. The carbon the plants already absorbed from the atmosphere is then naturally stored within these peat soils, helping to mitigate global warming. And though peat soils cover only about 3% of the global land surface, they contain over 600 gigatonnes of carbon and represent 44% of all soil carbon, making peatlands the world’s largest terrestrial carbon sink.

Plants and Forests

Plants and forests absorb carbon from the atmosphere through photosynthesis, which then becomes deposited and stored in forest biomass like tree trunks, branches, roots, and leaves. Large areas of trees and forests act as more significant carbon sinks simply because of their size and longer lifespans.

Grasslands also sequester a large amount of carbon. In places like California, where forests are more greatly threatened by wildfires and droughts, they could be considered more reliable carbon sinks than trees.

Ocean

The world’s oceans play a huge role in carbon sequestration, both by dissolving and absorbing CO2 from the surface water and also through photosynthesis by phytoplankton, seaweeds, and sea grasses. Microscopic plants called diatoms have been found to absorb 10 to 20 billion metric tons of carbon dioxide each year simply by floating on the surface of the ocean.

Coastal vegetation like mangrove forests are also massive contributors to global carbon sequestration (typically referred to as “blue carbon”) since the soils of marine plant habitats have a significantly higher rate of carbon absorption than terrestrial ecosystems.

Carbon Sinks and Climate Change

Carbon sinks are critical to managing the carbon levels in our atmosphere and ensuring that global warming is kept under control. The only problem is, carbon sinks have a maximum limit.

When carbon sinks are damaged or destroyed (for instance, as fires rage in the Amazon rainforest or when excess carbon in the ocean causes the water to become acidic), these ecosystems may stop absorbing carbon altogether and even emit stored carbon back into the atmosphere. Ocean warming, for instance, affects the ability of marine ecosystems to absorb CO2 because warmer water naturally absorbs less CO2 and because it stresses marine habitats that are designed to survive in cooler temperatures.

Burning fossil fuels like coal, oil, and natural gas is the greatest contributor to climate change by far. According to the United Nations, it accounts for almost 90% of all carbon dioxide emissions and over 75% of global greenhouse gas emissions.

Protecting Our Carbon Sinks

Natural carbon sinks that absorb CO2 perform biological carbon sequestration, but climate engineers are also developing new technologies that capture carbon from industrial sources and inject it into underground storage. However, these solutions come nowhere close to providing enough carbon storage to reduce current atmospheric CO2 concentrations and can’t replace the power of natural carbon sinks.

Unfortunately, human activity and subsequent increased CO2 release is upsetting the delicate balance between carbon and the earth’s atmosphere. Protecting and restoring our most indispensable carbon sinks and other important natural resources is essential to maintaining a stable future environment.