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Highlights

• The ambitious emissions reduction measures modeled in most global emissions pathways are not enough to achieve the Paris Agreement targets for limiting temperature rise. In these pathways, it is also necessary to undertake efforts to remove carbon dioxide (CO2) from the atmosphere at the gigaton scale—billions of metric tons per year globally.
• There is untapped potential to increase carbon removal in America’s forests and farms. However, although marginal costs of implementation are generally below US$50/tCO2, deploying these approaches at large scale will require addressing a set of needs related to scientific uncertainty, measurement, and monitoring; mechanisms to drive landowner adoption at large scale; and public funding.
• If these needs can be addressed, the potential scale of deployment in the United States is likely on the order of hundreds of millions of metric tons (MtCO2) per year.

Background

Heightened abatement of greenhouse gas (GHG) emissions is needed to achieve the goals of the Paris Agreement to limit warming to well below 2˚C, with efforts to limit warming to 1.5˚C, to avoid the most dangerous climate impacts. Furthermore, most scientific estimates show that to keep these goals within reach, the global emissions trajectory needs to not only reach net-zero by the second half of this century but continue downward into net-negative emissions. Global climate models therefore illustrate the need to pursue both aggressive emissions reductions and significant deployment of carbon removal. They rely upon carbon removal approaches to offset the last remaining GHG-emitting activities that are too challenging or expensive to eliminate, and to compensate for any temporary overshoot of temperature goals.

Carbon removal is the process of removing CO2 from the atmosphere and storing it. It is distinct both from solar radiation management, which seeks to reflect sunlight to reduce warming rather than remove carbon from the atmosphere, and from carbon capture and storage (CCS) from point sources of emissions such as fossil-fueled power plants or other industrial facilities. Approaches to carbon removal traverse a spectrum from land manage­ment approaches to technological options, including carbon management in agricultural soils, forests, and agroforestry; bioenergy with carbon capture and stor­age (BECCS); direct air capture and storage (DACS); and frontier technologies such as biochar, plant breeding or engineering, enhanced weathering, and seawater capture. The intention of carbon removal is to store CO2 in plants, soils, and oceans, as well as nonbiologically in geological formations and products (e.g., building materials), aug­menting the net transfer of carbon from the atmosphere that naturally takes place as part of the carbon cycle (Minx et al. 2018). In some cases, storage is permanent; in others the CO2 may return to the atmosphere over time.

To date, a gap exists between the need for rapid emissions reductions to stabilize the climate at the temperature targets established in the Paris Agreement, and the availability of cost-effective measures that can provide those reductions (UNEP 2017). Advancements in carbon removal can help close that gap. However, each carbon removal approach available today faces its own challenges, potential pitfalls, and limitations. The full potential of each remains uncertain. Given this uncertainty, a portfolio of approaches and technologies could yield greater opportunities for achieving large-scale carbon removal (Minx et al. 2018; Fuss et al. 2018).