Negative Emissions and The Long History of Carbon Removal

Authors: Wim Carton, Adeniyi Asiyanbi, Silke Beck, Holly J. Buck, Jens F. Lund

Prepared for the Institute for Carbon Removal Law and Policy

Recent IPCC assessments highlight a key role for large-scale carbon removal in meeting the objectives of the Paris Agreement. This focus on removal, also referred to as negative emissions, is suggestive of novel opportunities, risks, and challenges in addressing climate change, but tends to build on the narrow techno-economic framings that characterize integrated assessment modeling. While the discussion on negative emissions bears important parallels to a wider and older literature on carbon sequestration and carbon sinks, this earlier scholarship—particularly from the critical social sciences—is seldom engaged with by the negative emissions research community. In this article, we survey this “long history” of carbon removal and seek to draw out lessons for ongoing research and the emerging public debate on negative emissions. We argue that research and policy on negative emissions should proceed not just from projections of the future, but also from an acknowledgment of past controversies, successes and failures. In particular, our review calls attention to the irreducibly political character of carbon removal imaginaries and accounting practices and urges acknowledgment of past experiences with the implementation of (small-scale) carbon sequestration projects. Our review in this way highlights the importance of seeing continuity in the carbon removal discussion and calls for more engagement with existing social science scholarship on the subject. Acknowledging continuity and embracing an interdisciplinary research agenda on carbon removal are important aspects in making climate change mitigation research more responsible, and a precondition to avoid repeating past mistakes and failures.

Ambient Weathering Magnesium Oxide For Co2 Removal From Air

Authors: Noah McQueen, Peter Kelemen, Greg Dipple, Phil Renforth, Jennifer Wilcox

Full Citation: McQueen, N., Kelemen, P., Dipple, G., Renforth, P., and Wilcox, J. Ambient weathering of magnesium oxide for CO2 removal from air. Nat Commun 11, 3299 (2020).

Updated Abstract: 

To combat the dangerous effects of climate change, new technologies are needed to remove billions of tonnes of carbon dioxide (CO2) from the atmosphere. This paper analyzes the cost of a land-based process that uses a magnesium carbonate (magnesite, MgCO3) feedstock to repeatedly capture CO2 from the atmosphere. 

In this process, the initial magnesium carbonate feedstock is fed into a high temperature reactor, called a calciner. In the calciner, the magnesium carbonate is heated to produce magnesium oxide (MgO) and CO2, which is subsequently captured. The produced MgO is highly reactive with the CO2 in air; at ambient conditions, the MgO and CO2 react to re-produce magnesium carbonate materials. This high reactivity means the MgO can be transported to plots of land and used to naturally uptake CO2 from the ambient air. At the end of one year, the MgO will have reacted with CO2 to form magnesium carbonates. From here, the magnesium carbonates are transported back to the calciner, where they are once again heated to re-produce the MgO and release the atmospheric CO2 as a high-purity CO2 stream which can then be captured and stored or utilized. The process can then continue cyclically, making up for any losses by adding new MgCO3 into the calciner. 

Using an exploratory economic analysis, we estimate that this process could cost approximately 45 to 193 USD per tonne of CO2 captured from the air, considering the use of grid or solar electricity. The thermal energy for this process is provided by natural gas, which is combusted inside the calciner in pure oxygen, allowing for the co-capture of combustion-related CO2. The cost range presented here is large mainly on account of varying process parameters and uncertainty in the capital expenses.

This cyclical technology may achieve lower costs than optimistic projections for other direct air capture methods and has the scalable potential to remove 2 to 3 billion tonnes of CO2 per year, and thus may make a meaningful contribution to mitigate global warming.

California Announces New Actions to Fight Climate Change and Protect Biodiversity

Authored by Sydney J. Chamberlin, Ph.D. Climate Policy Associate, The Nature Conservancy in California

Record breaking heat waves. Massive mega-fires. Hurricane after hurricane. In a year wrought with disaster on global scales, these fingerprints of climate change serve as a poignant reminder that the time for climate action is now. With a recent Executive Order, California Governor Gavin Newsom lays out a new possible path for action – focusing on the role that natural and working lands can play in mitigating climate change and protecting biodiversity.

When sustainably managed, our natural and working lands – our forests, wetlands, grasslands, farmlands, rangeland, deserts and urban green spaces – provide a multitude of services that support thriving communities and habitat: they provide food, fiber, and recreational space; store and transport water; bolster local economies; support wildlife; buffer communities against floods, storms, and other disasters; and capture and store carbon. 

In the same way that our lands can act as a carbon sink, changes that impact soil organic matter and ecosystem health – including land-use modifications, deforestation, wildfires, and more – can result in stored carbon being released to the atmosphere. Ultimately, the dance between carbon stored and carbon released determines whether our lands function as a net sink of carbon or net source of carbon – and consequently, whether they serve as an asset or a liability in the fight against climate change. 

In the United States, managed forests and other lands have traditionally acted as net carbon sinks (EPA, 2020). However, over the past 150 years, land-use changes have added almost half as much carbon to the atmosphere as fossil fuel emissions (Houghton & Nassikas, 2017; Le Quéré et al., 2017) – and climate stressors are further driving changes in ecosystem carbon stocks, threatening to turn some of our lands into a net source of emissions (Sleeter et al., 2019). 

In light of this threat, decision-makers and governments are increasingly recognizing the role that strategic land management, conservation, and restoration activities (also known as nature-based climate solutions) can play in removing carbon from the atmosphere and sequestering it in soil and vegetation. 

These nature-based strategies provide climate mitigation benefits while they deliver a suite of additional environmental, economic and social benefits – enhancing both ecosystem and community resilience. Protecting people and nature from the worsening impacts of climate change will require swift and decisive action that recognizes the importance of natural and working lands and intact ecosystems. 

In 2020, California legislators led efforts to integrate nature into the State’s climate strategy. Assemblymember Kalra’s (aptly named) Assembly Bill 3030 aimed to protect 30% of the state’s land areas and water by 2030, aligning with an international “30 by 30” campaign that strives to avoid a point of no return for many of Earth’s species and ecosystems. Assembly Bill 2954, authored by Assemblymember Robert Rivas, would have required the State to set an overall climate goal for California’s natural and working lands and to identify methods to help the State utilize the natural and working lands sector in achieving its goal of carbon neutrality by 2045.

California’s new Executive Order, signed in October 2020, builds on the leadership of Assemblymembers Kalra and Rivas and advances some of the outcomes that Assembly Bills 3030 and 2954 strove to achieve. The Order calls for the State to protect 30% of the state’s water and land by 2030, and directs the California Natural Resources Agency to form a California Biodiversity Collaborative to help achieve this goal. 

The Order also acknowledges the critical role that the stewardship of natural and working lands must play in achieving the State’s climate change, air quality, water quality, equity, and biodiversity goals. It tasks California agencies with establishing a climate target for the natural and working lands sector and firmly establishes carbon sequestration as a part of the State’s climate strategy. The Order further directs State agencies to identify and implement strategies that will accelerate the removal of carbon with nature – while building climate resilience in California communities.

Accomplishing these ambitious goals will require the State to reexamine its current priorities and funding commitments – though there are also a number of non-monetary policy pathways that the State can use to elevate the role of natural and working lands in its climate action. 

The potential rewards of this action are substantial; a newly released report by The Nature Conservancy shows that implementing a suite of nature-based climate solutions could reduce more than 514 million metric tons of carbon dioxide cumulatively by 2050, with economic savings from avoided damages of more than $2.4 billion (The Nature Conservancy, 2020). The report shows that, in many cases, nature-based strategies can be dramatically scaled up by better aligning existing California policies and programs – and at a fraction of the cost of other methods such as industrial carbon capture. The many additional multiple benefits that accompany nature-based climate solutions provide another incentive to achieve the goals laid out by the Executive Order. 

In the post-COVID-19 world, restoring the vibrancy of California communities will require the State to balance climate action against other competing priorities. Nature is a powerful and cost-effective tool that the State can and should deploy to remove carbon. Implementing this tool will require shifting priorities and funding to match the urgency of the climate crisis. The time to act is now – and in acting to protect nature, California ensures that nature can help to protect us. 



EPA. (2020). Inventory of US Greenhouse Gas Emissions and Sinks. 

Houghton, R., & Nassikas, A. A. (2017). Global and regional fluxes of carbon from land use and land cover change 1850–2015. Global Biogeochemical Cycles, 31(3), 456–472.     

Le Quéré, C., Andrew, R. M., Friedlingstein, P., Sitch, S., Pongratz, J., Manning, A. C., …, Zhu, D. (2017). Global carbon budget 2017. Earth System Science Data Discussions, 10, 405–448.‐2017‐123   

Sleeter, B. M. , D. C. Marvin, D. R. Cameron, P. C. Selmants, A. L. Westerling, J. Kreitler, C. J. Daniel, J. Liu, and T. S. Wilson. (2019). Effects of 21st‐century climate, land use, and disturbances on ecosystem carbon balance in California. Global Change Biology 25(10):3334-3353. 

The Nature Conservancy. (2020). Nature-based Climate Solutions: A Roadmap to Accelerate Action in California. 

Managing Land‐based CDR: BECCS, Forests and Carbon Sequestration

Duncan Brack, Richard King

doi: 10.1111/1758-5899.12827


Decisions about when, where and how to achieve widespread carbon dioxide removal (CDR) are urgently required. Delays in developing the requisite policy and regulatory frameworks increase the risks of overshooting climate goals and will necessitate much larger negative emissions initiatives in the future. Yet the deployment of bioenergy with carbon capture and storage (BECCS) at the scales assumed under most ParisAgreementcompliant emissionreduction pathways is unlikely. More generally, the sustainability of largescale BECCS is questionable given its extensive land, water, and energy requirements for feedstocks and the competing necessity of these resources for the provision of ecosystem services and attainment of multiple Sustainable Development Goals. BECCS on a more limited scale, however, could have more benign impacts if feedstocks were restricted to wastes and residues. There is also widespread recognition that extensive afforestation, reforestation and forest restoration have critical roles in reducing greenhouse gas emissions to net zero. To date there has been little focus on the optimum strategies for integrating landbased CDR approaches – under which circumstances forest areas are best left undisturbed, managed for conservation, and/or managed for harvested wood products, and how these options affect the availability of residual feedstocks for BECCS. This paper reviews this debate and suggests appropriate policy measures.

Three principal policy implications emerge:

First, the necessity of abandoning the assumption, common in integrated assessment models, that BECCS is the preeminent carbon removal solution. Rather it needs to be analysed alongside all other negative emissions technologies (NETs), on the basis of full lifecycle carbon balances (including dropping the assumption that biomass feedstock is inherently carbonneutral), as well as other ecosystem and sustainability cobenefits and tradeoffs.

Second, urgent action is required to scale up the development and deployment of sustainable NETs. No single NET – whether BECCS, naturebased, or otherwise – will achieve the scale of CDR required in the vast majority of 1.5°C and 2°C mitigation scenarios, let alone do so sustainably. But portfolios of multiple NETs, deployed sensitively at modest scales, will be invaluable for achieving climate security. This requires designing policy and financial mechanisms that are sufficiently attuned to the contextual specificities of each potential deployment, but which are sufficiently catalytic to galvanise appropriate and complementary actions at adequate scales and with enough urgency.

Third, we need to be absolutely clear that all CDR efforts have to be additional to – not substituting for, or detracting from – urgent acceleration of conventional abatement actions. This means we need to accelerate conventional abatement action as rapidly as possible. There are too many drawbacks and uncertainties associated with BECCS and other NETs to place excessive reliance on them – though carbon removal solutions will undoubtedly be needed.