Despite several emission reduction efforts, the atmospheric concentration of carbon dioxide remains significantly high. This is where carbon removal technologies come into play. Carbon dioxide removal (CDR) sequesters atmospheric carbon dioxide and locks it away for centuries and millennia. Also known as negative emissions technologies (NETs), this approach holds immense promise in combating the negative effects of climate change that have become rampant, including wildfires and heatwaves.
Planting trees, biomass carbon removal and storage (BiCRS), direct air capture, carbon mineralization, and ocean-based CDR are the primary strategies for carbon removal. Trees naturally remove carbon dioxide from the atmosphere through photosynthesis and convert it into carbon stored in the soil and wood. Expanding and restoring forest covers significantly leverages photosynthesis, and this can be done using several approaches, such as restoring forests damaged by wildfire or diseases, integrating trees into animal agricultural farms, planting trees in crop farms, and encouraging urban reforestation.
BiCRS is a variety of techniques that utilize biomass, the renewable organic matter in plants, to sequester atmospheric carbon dioxide and store it for extended durations. These methods optimize plants’ carbon sequestration capabilities beyond their natural life cycles. Unlike trees that capture and store carbon until they decay, BiCRS seeks to remove the carbon dioxide that trees store permanently.
There are several methods for carbon removal using biomass, including the production of biochar, which involves heating biomass at high temperatures in environments with limited oxygen to yield a charcoal-like soil additive that effectively sequesters carbon in the soil. Bio-oil production is another method where biomass is heated at high temperatures, resulting in a liquid injected and permanently stored underground.
Additionally, carbon-rich biomass can be permanently stored in secure vaults. Another option for carbon removal is Bioenergy Carbon Capture and Storage (BECCS), wherein biomass is used to generate energy, and subsequent carbon dioxide emissions are captured and sequestered.
On the other hand, direct air capture is a technology that extracts carbon dioxide directly from the atmosphere. Direct air capture systems use chemical solvents to trap carbon dioxide molecules, concentrate and store them in long-lived commodities like concrete, or utilize them in various applications, such as synthetic fuel production. Direct air capture has the potential for achieving negative emissions, helping to offset emissions from sectors that are hard to restrict.
Carbon mineralization is a process that converts carbon dioxide into stable carbonate minerals, effectively removing it from the atmosphere. This natural process occurs over geological timescales, but various techniques can accelerate this process, such as exposing rocks to carbon-rich environments. Carbon mineralization offers a promising solution for long-term carbon sequestration, as the resulting carbonate minerals can remain stable for thousands to millions of years. Additionally, carbon mineralization can address carbon emissions from industrial sources by permanently locking away captured carbon dioxide.
Lastly, ocean-based carbon removal sequesters atmospheric carbon dioxide and stores it in the ocean to mitigate climate change. This is achievable through several approaches, including ocean fertilization, where nutrients such as iron or nitrogen are introduced into nutrient-deprived ocean areas to stimulate phytoplankton growth. As phytoplankton photosynthesize, they draw carbon dioxide from the atmosphere, and upon their death, some of the carbon sinks into the ocean.
Blue carbon is an alternative approach that conserves and restores coastal ecosystems such as mangroves, seagrasses, and salt marshes. These ecosystems are highly efficient at sequestering carbon dioxide in their biomass and sediments. Moreover, experts are exploring injecting captured carbon dioxide into the deep ocean directly to sequester carbon.
