Carbon dioxide removal

[12]: 8  There is potential to remove and sequester up to 10 gigatons of carbon dioxide per year by using those CDR methods which can be safely and economically deployed now.

The term geoengineering (or climate engineering) is sometimes used in the scientific literature for both CDR or SRM (solar radiation management), if the techniques are used at a global scale.

[7]: 114 After net zero emissions have been achieved, CDR could be used to reduce atmospheric CO2 concentrations, which could partially reverse the warming that has already occurred by that date.

[22][23] The possibility of large-scale future CDR deployment has been described as a moral hazard, as it could lead to a reduction in near-term efforts to mitigate climate change.

[21]: 124 [12] However, the 2019 NASEM report concludes: "Any argument to delay mitigation efforts because NETs will provide a backstop drastically misrepresents their current capacities and the likely pace of research progress.

[24] Experts also highlight social and ecological limits for carbon dioxide removal, such as the land area required.

[25] Forests, kelp beds, and other forms of plant life absorb carbon dioxide from the air as they grow, and bind it into biomass.

For example, natural events, such as wildfires or disease, economic pressures and changing political priorities can result in the sequestered carbon being released back into the atmosphere.

Afforestation and reforestation – sometimes referred to collectively as 'forestation' – facilitate this process of carbon removal by establishing or re-establishing forest areas.

[29]: 26–28 Depending on the species, the trees will reach maturity after around 20 to 100 years, after which they store carbon but do not actively remove it from the atmosphere.

[29]: 26–28  Carbon can be stored in forests indefinitely, but the storage can also be much more short-lived as trees are vulnerable to being cut, burned, or killed by disease or drought.

[33] Agricultural methods for carbon farming include adjusting how tillage and livestock grazing is done, using organic mulch or compost, working with biochar and terra preta, and changing the crop types.

It is created using a process called pyrolysis, which is basically the act of high temperature heating biomass in an environment with low oxygen levels.

[38][better source needed] However, at the moment, biochar is restricted by the terrestrial carbon storage capacity, when the system reaches the state of equilibrium, and requires regulation because of threats of leakage.

A 2021 report on CDR indicates that there is medium-high confidence that the technique could be efficient and scalable at low cost, with medium environmental risks.

[45] Ocean fertilization is estimated to be able to sequester 0.1 to 1 gigatonnes of carbon dioxide per year at a cost of USD $8 to $80 per tonne.

[46] The removal potential of alkalinity enhancement is uncertain, and estimated at between 0.1 to 1 gigatonnes of carbon dioxide per year at a cost of USD $100 to $150 per tonne.

[47] Preliminary estimates suggest that the cost of such carbon removal can be paid for in large part if not entirely from the sale of the desalinated water produced as a byproduct.

[48] The cost of CDR differs substantially depending on the maturity of the technology employed as well as the economics of both voluntary carbon removal markets and the physical output; for example, the pyrolysis of biomass produces biochar that has various commercial applications, including soil regeneration and wastewater treatment.

[50][51] The fact that biochar commands a higher price in the carbon removal market than nature-based solutions reflects the fact that it is a more durable sink with carbon being sequestered for hundreds or even thousands of years while nature-based solutions represent a more volatile form of storage, which risks related to forest fires, pests, economic pressures and changing political priorities.

[57][58] After the diffusion of net-zero targets, CDR plays a more important role in key emerging economies (e.g. Brazil, China, and India).

[59] As of early 2023, financing has fell short of the sums required for high-tech CDR methods to contribute significantly to climate change mitigation.

[60] Such as a private sector alliance led by Stripe with prominent members including Meta, Google and Shopify, which in April 2022 revealed a nearly $1 billion fund to reward companies able to permanently capture & store carbon.

"[61] The predominance of private sector funding has raised concerns as historically, voluntary markets have proved "orders of magnitude"[60] smaller than those brought about by government policy.