Biosequestration involves capturing and storing atmospheric carbon dioxide (CO2) through biological processes. This natural phenomenon removes CO2 from the air, integrating it into living organisms and ecosystems. The stored carbon helps mitigate rising atmospheric CO2 levels, which influence global climate patterns.
The Core Process
Biosequestration relies on photosynthesis, where plants, algae, and some bacteria use sunlight to convert atmospheric CO2 and water into sugars for energy. Carbon from the CO2 incorporates into organic matter, forming living tissues. This carbon is then stored within the biomass of these organisms, such as in plant stems, leaves, and roots.
When photosynthetic organisms die, their carbon-rich organic matter transfers into soil or marine sediments. Microorganisms break down this material, and a portion of the carbon stabilizes in these environments, preventing its immediate release back into the atmosphere. This process continuously cycles carbon, with some sequestered for varying durations in natural reservoirs.
Natural Biosequestration Methods
Natural ecosystems are significant carbon sinks. Forests and terrestrial ecosystems absorb CO2. Trees and other plants store carbon in their woody biomass, leaves, and extensive root systems. Reforestation, replanting trees on deforested land, and afforestation, planting trees on land without prior forest cover, enhance this natural carbon uptake.
Oceans also function as major carbon reservoirs, absorbing approximately 25% of human-caused CO2 emissions annually. Marine organisms, especially microscopic phytoplankton, absorb dissolved CO2 from surface waters through photosynthesis. This process moves carbon from the surface to deeper ocean layers as organisms die and sink, or through the food web. Carbon is then sequestered in ocean waters and sediments for hundreds to thousands of years.
Soils are another vast carbon repository, holding approximately 75% of Earth’s terrestrial carbon. Organic matter from decomposing plant and animal residues, along with microbial activity, contributes to soil organic carbon (SOC). This carbon stabilizes within soil aggregates and through interactions with soil minerals, allowing it to be stored for extended periods. Practices like no-till farming and cover cropping increase carbon sequestration in agricultural soils.
Engineered Approaches
Engineered methods leverage biological processes to enhance carbon sequestration. Bioenergy with Carbon Capture and Storage (BECCS) involves growing biomass which absorbs CO2 during its growth. This biomass is then used to produce energy, and the CO2 released during combustion is captured and stored in geological formations deep underground, preventing atmospheric release. BECCS aims for net-negative emissions by permanently removing CO2 initially absorbed by plants.
Biochar is another engineered approach, created by heating biomass in a low-oxygen environment (pyrolysis). This converts organic materials into a stable, carbon-rich substance added to soil. Biochar’s porous structure retains carbon in the soil for hundreds to thousands of years, preventing its decomposition and release as CO2. Biochar also improves soil fertility and water retention.
Algae cultivation offers rapid CO2 absorption. Microalgae and macroalgae (seaweed) efficiently convert CO2 into biomass through photosynthesis. Some algae fix CO2 10 to 50 times more efficiently than terrestrial plants. Cultivated algae biomass can be used for biofuels or bioproducts, with potential for carbon storage if sequestered permanently, such as by sinking biomass to the deep ocean.
Importance for Climate Stability
Biosequestration addresses climate change by removing CO2 from the atmosphere, contributing to climate stability by reducing greenhouse gas concentration. Enhancing natural carbon sinks through sustainable land management and innovative technologies supports climate mitigation.
Long-term carbon storage in forests, oceans, and soils is crucial for managing atmospheric carbon. These processes are a key component of strategies for achieving climate goals and fostering a sustainable future. Understanding and supporting biosequestration allows humanity to work with natural systems to manage atmospheric carbon.