What are the different methods of carbon sequestration and how do they work?
Carbon sequestration refers to the process of capturing and storing carbon dioxide (CO2) from the atmosphere to mitigate climate change. There are several methods of carbon sequestration, including terrestrial, geological, and oceanic approaches. Terrestrial methods involve enhancing natural processes like afforestation (planting trees) and reforestation, which absorb CO2 through photosynthesis and store it in biomass and soils. Geological methods entail injecting captured CO2 deep underground into geological formations or depleted oil and gas reservoirs, where it is trapped and stored safely over long periods of time. Oceanic carbon sequestration includes biological approaches like promoting phytoplankton growth to absorb CO2, as well as direct injection of CO2 into deep seawater or sediments.
Long answer
Carbon sequestration comprises various techniques aimed at reducing the amount of carbon dioxide in the atmosphere by capturing and storing it. Terrestrial methods involve utilizing vegetation to absorb atmospheric CO2. Afforestation involves planting new forests on areas that were previously devoid of trees, while reforestation focuses on restoring forests on previously deforested lands. Both approaches use the power of photosynthesis, a natural process where plants capture CO2 from the air, convert it into organic compounds through photosynthesis, and store most of the carbon in their biomass (stems, leaves) as well as in soils.
Geological methods involve capturing CO2 emissions directly from large stationary sources such as power plants or industrial facilities before they are released into the atmosphere. The captured CO2 is then transported via pipelines or ships to suitable geological formations for storage. Common storage options include deep saline aquifers (porous rock formations filled with salty water), depleted oil and gas reservoirs, or unmineable coal seams. In these formations, impermeable rock layers cap porous structures beneath the surface to provide secure trapping mechanisms that prevent the stored CO2 from leaking over long periods.
Oceanic carbon sequestration methods are broadly divided into biological and direct injection approaches. Biological methods utilize the potential of marine plants, mostly phytoplankton, to absorb CO2 through photosynthesis. By promoting phytoplankton growth in specific areas, such as ocean fertilization or iron enrichment zones, these plants can draw down significant amounts of atmospheric CO2 and eventually transfer it to deep ocean sediments through organic matter sinking.
Direct injection methods involve the injection of captured CO2 into the surface waters of the oceans or deep below them. In surface ocean CO2 injections, the gas dissolves in seawater and is subsequently transported to the deep ocean through circulation patterns where it can be stored for extended periods. In deep Ocean Sequestration (DOS) approaches, CO2 is directly injected into deep waters or sediments below a few thousand meters where it can either dissolve into the water or react with minerals present in sediments to form stable mineral carbonates.
To effectively address climate change, a combination of these carbon sequestration methods may be required. However, it’s important to consider potential challenges like cost, environmental impacts, reliable monitoring and verification techniques, and setting robust legal frameworks to ensure long-term storage integrity while minimizing unintended consequences.