More is More: A Case for Expanded Life Cycle Assessment (LCA) for Carbon Dioxide Removal (CDR) Applications

Why CDR Is Unique

The goal of carbon dioxide removal (CDR) is greenhouse gas (GHG) mitigation, which necessitates a framework to measure corresponding removals and emissions over a complete life cycle. Life cycle assessment (LCA)-based accounting has served as the consistent basis for this assessment by calculating “net removals” associated with various CDR projects.

There are environmental attributes of CDR that warrant a broad suite of environmental impact categories to illuminate potential tradeoffs:

• Reliance on directly enhancing naturally occurring ecosystem processes that result in potential dynamic impacts that may not be evident.
• The scale required to limit warming is on the order 5–10 gigatonnes annually, meaning that potential tradeoffs could also be large.
• CDR approaches are diverse, and there is a desire to assess them broadly as a potential portfolio of solutions.

Many CDR approaches have the potential to not only remove carbon dioxide but also to provide other ecosystem services, yielding co-benefits. To appropriately quantify those benefits, it is necessary to consider a broad scope of impacts.

Some CDR registry protocols and standards have also included assessments of a broader set of environmental and societal impacts, sometimes referred to as “sustainability metrics” or “sustainability criteria.” These include characterizing metrics such as water quality and availability, soil health, air quality, biodiversity/conservation, and responsible waste management. Assessment of these criteria is an important step towards considering the performance and potential impacts of a project.

However, these assessments are based on heuristics, and we do not yet have enough experience to provide insight as to the potential trade-offs in other environmental impacts, especially for specific deployment locations. This begs for standardization of the approach to ensure consistency and depth.

LCA: An Approach for Expanding Beyond Carbon Footprinting

LCA and carbon footprinting are analysis frameworks that evaluate a product or system from cradle-to-grave. Over the years, these terms have been used largely synonymously; however, there are important differences in the scope of impacts evaluated.

Carbon footprinting (ISO 14067) is considered to be a subset of LCA that focuses solely on GHG emissions and the corresponding global warming potential (GWP) of the system. LCA is an ISO (14040/14044) standardized, multi-criteria framework that provides a holistic view of the potential environmental impacts attributed to a product or service throughout its entire life cycle.

For LCA in the U.S., we often focus on the environmental impacts defined in the EPA’s Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI). These include categories such as ozone depletion, acidification, eutrophication, smog formation, human health impacts, and ecotoxicity and can be complemented with other methods, such as water stress. 

Motivation for Exploring Broader Impacts

Avoiding unintended consequences is the motivation for considering a broad scope of environmental impacts. This helps us illuminate trade-offs and avoid less favorable outcomes that have been observed in historical applications of policy and technology. These include tradeoffs associated with the addition of the oxygenate MTBE to gasoline, shifts in burdens of air quality impacts to downwind communities through the use of tall smokestacks to mitigate air pollutants through dilution and dispersion, and increases in water pollution due to fertilizer runoff as a result of biofuels mandates in the U.S. through the Renewable Fuels Standard (RFS).

LCA in isolation would not have mitigated these outcomes; however, by adhering to a standardized framework focused on a broad set of impacts, it forces us to identify potential trade-offs and explore them further through an appropriate assessment of risks and benefits.

Doing a robust LCA is not easy. Evaluating a wide range of environmental impacts is data-intensive and fraught with uncertainty, especially for emerging technologies. Once the compiled data is sufficient to inform the impact assessment, the next challenge is interpreting multiple results with different metrics that may conflict across different impact categories.

Some impacts, such as ozone depletion and climate change, are global in scale, whereas others, such as smog formation, eutrophication, and water scarcity, are highly localized. LCA can illuminate tradeoffs, but other tools must be leveraged in combination to help facilitate decisions. 

Moving forward, we recommend that CDR protocols and standards leverage LCA to its fullest extent—to holistically explore systems so that there is a clear understanding of tradeoffs to balance CO2 removals and potential adverse environmental impacts. Using LCA as a framework will ensure a robust assessment of sustainability criteria and metrics. Optimal CDR projects should not only be cost-effective but also environmentally effective, considering removals in relation to potential ecosystem impacts.

Greg Cooney

Senior Fellow

Greg Cooney is a senior fellow at the Kleinman Center. He previously served as director of the policy and analysis division in the U.S. Department of Energy’s Office of Carbon Management.

Michael Shell

Carbon Removal Scientist, Isometric

Michael is a Carbon Removal Scientist at Isometric. He previously served as a Senior Analyst with the U.S. Department of Energy’s Office of Energy Efficiency & Renewable Energy, and an Economist in the Office of Transportation and Air Quality at the U.S. Environmental Protection Agency.

Jennifer Wilcox

Presidential Distinguished Professor

Jen Wilcox is Presidential Distinguished Professor of Chemical Engineering and Energy Policy. She previously served as Principal Deputy Assistant Secretary for the Office of Fossil Energy and Carbon Management at the Department of Energy.