CARBON REMOVAL

Carbon removal is the process by which humans actively and intentionally remove carbon dioxide (CO2) from the atmosphere and store it in longer-lived reservoirs.

CARBON REMOVAL

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Carbon removal is the process by which humans actively and intentionally remove carbon dioxide (CO2) from the atmosphere and store it in plants, soils, oceans, geological reservoirs, or in long-lived products like cement. Carbon removal actions are typically distinct from important, natural CO2 uptake processes; rather, carbon removal focuses on direct removal initiated through human intervention.

There is a wide range of popular carbon removal strategies. Some are entirely focused on enhancing natural systems, some deploy high-tech engineered solutions, and others combine engineering with natural approaches. Technologies used to remove carbon are sometimes referred to as "negative emissions technologies (NETs)" or “carbon containment”, due to the ability of those technologies to remove CO2 from the atmosphere and contain it in geologic reservoirs and terrestrial ecosystems. [1]

Carbon removal is a field ripe for innovation and testing. Many governments, universities, companies, and non-profits are working to find and test carbon removal solutions that are technologically and economically feasible, as well as environmentally benign and socially just.

Curated by:

Dr. Anastasia O’Rourke

Managing Director

Yale Carbon Contaiment Lab

With help from:

Claire Goydan

Some examples of negative emissions technologies (NETs) [a]

Why is carbon removal rising in prominence as a climate strategy?

Removing and containing CO2 and other greenhouse gases could dramatically reduce climate risk if done at scale. Carbon removal approaches complement existing efforts to reduce or avoid greenhouse gas emissions, and also complement the immediate need for investment in resilience and adaptation to the effects of climate change.

CO2 emissions are a potent greenhouse gas, contributing to global climate change. Once in the atmosphere, CO2 is expected to reside there for thousands of years. Even if humans were to stop all CO2 emissions today, the effects of global climate change would continue for decades to come. To limit global warming to 1.5˚C and to reach “net zero” emissions goals as called for by the Paris Climate Accord, many climate models predict that a massive scale up in carbon removal may be necessary. Some climate models indicate that to achieve this could require upwards of 10 Gt/yr of CO2 removed from the atmosphere by 2070[2]. According to the National Academy of Sciences in 2019, we need to remove approximately 700 billion tons (Gt) of CO2 or equivalent by the year 2100.

Of course, how much carbon removal we will need depends on how much we reduce emissions, and over what time scale. Part of the driver for developing carbon removal solutions is the necessity to act quickly while research and development is conducted to find safe alternatives for greenhouse gas emissions that are currently hard to avoid. Such ‘hard to avoid’ emissions sources include:

Nitrous oxide from agricultural, waste, and wastewater sources
Aviation and shipping fuels
Building heating fuels

Carbon removal approaches are still at an early stage in their development, and there is much work to be done to design systems that can be environmentally safe, economically feasible, and deployed at scale.

Examples of carbon removal activities include:

BIOMASS

Burial of biomass, treatment of biomass to slow decay

Limit decomposition and aerobic respiration and decay of biomass through burial and/or encasement.

GEOLOGIC STORAGE

1. Carbon capture and storage
2. Biomass to carbon capture and storage (BECCs)
3. Direct air capture with carbon storage (DAC)

Long term or permanent storage of CO2 in geologic formations such as saline aquifers or basalts.
Sequestration of CO2 in biomass to energy systems coupled with CO2 capture and storage.
Separation of CO2 from air, coupled with geologic storage.

MINERALS

Mineralization, enhanced weathering

Reaction of minerals with CO2 to form solid carbonate minerals such as calcite or magnesite.

SOILS

Agricultural soil management, soil amendments, reduced tillage, cover crops, agroforestry, biochar

Improve soil capacity to store carbon. Increase amount of carbon deposited in and retained in both organic and inorganic forms.

FORESTS

Reforestation, afforestation, improved forest management

Regrowth of degraded forests, sequestration of CO2 in newly grown forests and regrowth of degraded forests; restoration of forests to protect from wildfire risk and to enhance rates of carbon sequestration

OCEANS

Increased ocean alkalinity, ocean fertilization, marine biomass management and cultivation

Enhancement of stored inorganic carbon in the ocean through increasing alkalinity. Cultivation of macro- and micro- algae in marine ecosystems. Adding nutrients to the upper layers of the ocean to stimulate photosynthesis. Burial of marine biomass.

PRODUCTS

Storing carbon in materials e.g. concrete, mass timber, insulation

Curing concrete with CO2, integration of mineralized carbon materials and plant fibers into building products, use of timber for structural buildings.

WETLANDS AND

PEATLANDS

Peat re-wetting and/or restoration,

coastal blue carbon

Storage of carbon in soil and biomass of wetlands or peatlands.

Watch to learn more about carbon removal, its implications as a climate change mitigation strategy, and the various carbon removal options, from WRI.

Here are some useful resources to learn more about carbon removal:

Learn about the research and initiatives occurring at Yale's Carbon Containment Lab:

Explore the Carbon Dioxide Removal Primer, written and curated by many of the academics and non-profits working most closely on carbon removal:

Read a comprehensive report on negative emissions technologies from the National Academies of Sciences, Engineering, and Medicine:

Read The Economist's breakdown of carbon removal and what needs to be done:

Explore WRI's resources on carbon removal (and watch their video above!):

Read The Royal Society's report on processes and methods for carbon removal:

Footnotes

[1] National Academies of Science, 2019, Negative Emissions Technologies and Reliable Sequestration: A Research Agenda http://nap.edu/25259

[2] AVOID 2 model cited in OECD, 2018, Innovation for the Low Carbon Economy https://www.oecd.org/environment/cc/g20-climate/collapsecontents/Imperial-College-London-innovation-for-the-low-carbon-economy.pdf

[3] National Academy of Sciences, 2019, Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. https://www.nap.edu/catalog/25259/negative-emissions-technologies-and-reliable-sequestration-a-research-agenda

[a] Caldecott, B., Lomax, G., & Workman, M. (2015). Stranded carbon assets and negative emissions technologies.

Chicago