In this discussion, CGS Assistant Research Scholar Jay Fuhrman will cover new model developments for carbon management technologies as well as their role in meeting Nationally Determined Contribution pledges under the Paris Agreement.
Abstract: In the decade since the Paris Agreement, the expected role of carbon dioxide removal (CDR) in limiting end-of-century temperature increase to “well- below 2C” has grown substantially. CDR will be critical to reduce net greenhouse gas (GHG) emissions in the short to medium-term, and to compensate for carbon budget overshoot in the longer term by enabling net-negative global emissions. Despite this, most countries remain vague about how they will deliver the large-scale removals implied in their Nationally Determined Contributions (NDCs) and Long-Term Strategies (LTS) under the UNFCCC. To the extent that countries have considered CDR in these submissions, they have generally relied heavily on an expansion of their land carbon sink by increasing forest area. Others have used bioenergy with carbon capture and storage (BECCS) as a proxy for all CDR. However, relying solely on these CDR pathways could lead to unacceptable strain on the land system, and/or reversibility risks. Alternative methods, such as direct air carbon capture and storage (DACCS), enhanced rock weathering (ERW), and biochar (BC), may offer the prospect of higher durability and/or near-term scalability. These limitations are due in part to limits on integrated assessment models (IAM), which have long supported Working Group III reports and helped to guide national decarbonization strategies. But their realism and usefulness with respect to CDR has been hindered for several reasons. First, only recently have models begun to represent CDR pathways beyond BECCS and afforestation on a widespread basis. Second, scenarios often use stylized global emissions pathways and/or end-of-century warming targets, which do not necessarily reflect real-world policy commitments across nations. Critically, rate and growth limits for different CDR approaches, or enabling technologies such as geological carbon storage, are not considered a systematic matter for individual countries or regions in these scenarios. Finally, the additional costs of measurement, monitoring, reporting and verification (MMRV) are often not reflected in the technoeconomic literature used to parametrize IAM input assumptions.
To begin addressing these limitations, we present the results of a 3-model intercomparison study on the role of a portfolio of CDR in the NDCs and long-term strategies. Each of the three models differs in the breadth and depth of CDR technology representation, but all have been updated to reflect the latest science on CDR and associated enabling sectors, such as geological carbon storage. These developments are then applied in an series of scenarios based on NDC pledges submitted as of June 2025 to evaluate the potential for CDR pathways in regions around the world in meeting their emissions reduction targets. Initial efforts to reflect MMRV costs for various CDR pathways in the GCAM model will also be presented.