Carbon removal is the process of removing carbon dioxide from the atmosphere and locking it away for decades, centuries, or millennia. This could slow, limit, or even reverse climate change—but it is not a substitute for cutting greenhouse gas emissions. This is because carbon removal is generally slow-acting and may not be able to be deployed at scales commensurate with society’s current greenhouse emissions. Carbon removal is sometimes referred to as carbon dioxide removal or CDR, and technologies for implementing carbon removal are sometimes called Negative Emissions Technologies (NETs).
Some prominent ideas for carbon removal include:
- planting massive new forests (afforestation/reforestation)
- using no-till agriculture and other practices to increase the amount of carbon stored in soils (soil carbon sequestration)
- creating charcoal and burying it or plowing it into fields (biochar)
- capturing and sequestering carbon from biofuels and bioenergy plants (bioenergy with CCS or BECCS)
- spreading crushed rocks over land to absorb carbon dioxide from the air or exposing them to carbon dioxide-rich fluids (enhanced mineralization)
- building machines that would suck carbon dioxide directly out of the atmosphere and bury it (direct air capture)
- oceans-based methods, including:
- spreading alkaline materials, such as lime, over the ocean (ocean alkalinization)
- fertilizing selected areas of the ocean by spreading nutrients, such as iron, over the surface (ocean fertilization)
- fertilizing selected areas of the ocean by pumping nutrient-rich waters from the depths to the surface (artificial upwelling)
- accelerating the transport of carbon to the ocean depths by pumping surface waters downward (artificial downwelling)
Similar methods for capturing and storing other greenhouse gases, such as methane, are known as greenhouse gas removal.