Month: November 2020

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

https://doi.org/10.1002/wcc.671

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.

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). https://doi.org/10.1038/s41467-020-16510-3

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.

Duncan Brack, Richard King

doi: 10.1111/1758-5899.12827

Abstract

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 Paris‐Agreement‐compliant emission‐reduction pathways is unlikely. More generally, the sustainability of large‐scale 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 land‐based 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 pre‐eminent 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 carbon‐neutral), as well as other ecosystem and sustainability co‐benefits and trade‐offs.

Second, urgent action is required to scale up the development and deployment of sustainable NETs. No single NET – whether BECCS, nature‐based, 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.