Dissertation
Responsible Removals: Holistic Portfolio Design, Systems Integration, and Equitable Allocation of Carbon Dioxide Removal
Limiting global warming to 1.5°C will require aggressive emission reductions and large-scale CO₂ removal from the atmosphere. Carbon Dioxide Removal (CDR) can neutralize hard-to-abate residual emissions and even draw down atmospheric CO₂ to reverse a temperature overshoot. However, deploying CDR at the gigatonne scale poses major challenges: if done without care it could threaten ecosystems, food security, or climate justice.
- Author
- O.R. Rueda González
- Date
- 13 May 2026
- Links
- Thesis in Leiden Repository
This thesis is centered on the concept of “responsible removals,” which means deploying CDR in a scientifically sound, sustainable, and equitable manner. It advances the analytical foundation for responsible CDR by addressing three interlinked questions: what CDR methods to prioritize, how to integrate CDR sustainably into natural and human systems, and who should bear responsibility for CDR efforts. These questions correspond to three core challenges—holistic portfolio design, sustainable systems integration, and equitable allocation—which are examined in Chapters 2, 3, and 4, respectively.
Chapter 2: Holistic portfolio design. This chapter develops and applies a multi-criteria framework to evaluate a diverse CDR methods, going beyond the conventional cost-only approach. The analysis incorporates criteria such as technological feasibility, durability of carbon storage, speed of climate impact, resource needs, and co-benefits or side effects. This holistic assessment reveals that the prioritization of CDR options shifts markedly when broader criteria are considered. For example, Direct Air Carbon Capture and Storage (DACCS), which offers highly permanent CO₂ storage and scalable deployment, rises to the top rank under balanced criteria, even though it is relatively costly, because of its strong performance on effectiveness and governance feasibility. In contrast, “low-cost” land-based solutions like afforestation or certain bioenergy with carbon capture and storage (BECCS) options drop in priority once factors like land use, impermanence of carbon in plants, and governance challenges are accounted for. The results underscore that no single CDR method can dominate a responsible removal strategy: every option has trade-offs, and an optimal strategy requires a portfolio of methods. Chapter 2 demonstrates that a diversified CDR portfolio, chosen via transparent multi-criteria evaluation rather than narrow least-cost optimization, would be more robust and aligned with society’s broader objectives (climate effectiveness, sustainability, and risk mitigation).
Chapter 3: Sustainable systems integration. This chapter examines how CDR deployment can be coordinated with transformative changes in other sectors to overcome resource constraints – in particular, it explores the synergy between a global dietary transition and BECCS. The study asks whether shifting the world’s protein supply from animal products to plant-based alternatives (a major demand-side climate mitigation action) could free up enough agricultural land to facilitate large-scale CDR via bioenergy. The analysis finds that a worldwide protein transition offers a systemic solution to land-use competition: in an ambitious scenario where animal-sourced foods are largely replaced, on the order of 3,000 million hectares of pasture and cropland could be liberated by 2050 (roughly 60% of today’s agricultural area). The research assessed the bioenergy crop potential over 1,947 Mha of such area. Even under more moderate dietary shifts, a vast land area is freed for other uses. Crucially, the spatial analysis shows that most of this potential biomass-growing land is geographically well-aligned with places suitable for CO₂ storage. Approximately 61% of the biomass cultivation areas identified lie within 300 km of a viable geological storage basin for carbon, with a global average transport distance of only around 250 km. This tight source-sink coupling greatly enhances the feasibility of BECCS by minimizing transport and infrastructure hurdles.
Building on that land-resource synergy, Chapter 3 quantifies the carbon removal and energy potential of BECCS when using bioenergy crops grown on the liberated farmland. Under a scenario of a 50% global shift to plant-based proteins by 2050, the freed land could sustainably support bioenergy crop cultivation that feed BECCS power plants, yielding on the order of 6–9 gigatonnes of CO₂ removal per year. At the same time, these BECCS facilities would produce roughly 25–40 exajoules of electricity annually, comparable to about 25–40% of today’s global electricity supply – or alternatively, a substantial quantity of carbon-neutral liquid fuels or hydrogen. Notably, these estimates represent net removals, accounting for the full life-cycle emissions (e.g. from cultivation, transport, and processing) and even the “opportunity cost” of foregone natural carbon uptake if the land were instead left to revert to natural grassland or forest. The analysis is conducted under strict sustainability safeguards: it ensures that food production remains sufficient for the growing population, prevents any expansion of agriculture into intact ecosystems, and limits irrigation to protect water resources. Even with these constraints, the findings indicate that integrating demand-side dietary change with CDR supply can unlock a multi-gigatonne negative emissions potential that was previously thought implausible for BECCS due to land limitations. In summary, Chapter 3 illustrates that CDR need not be planned in isolation. By co-transforming the food system, we can dramatically expand sustainable CDR capacity while also achieving co-benefits like reduced agricultural emissions and improved public health.
Chapter 4: Equitable allocation of CDR responsibility. The final study introduces a stock-based metric to complement fossil-focused responsibility accounts: the land-use carbon debt, defined as the present-day terrestrial carbon stock deficit between carbon stored in currently managed lands (cropland, pasture and managed forests) and their potential natural carbon stocks in vegetation and soils. The analysis estimates a global land-use carbon debt of ~1,470 GtCO₂ in 2020, comparable in magnitude to cumulative fossil CO₂ emissions since the Industrial Revolution. Linking these stock deficits to production and trade enables both production- and consumption-based attribution (with trade-based allocation from 1970 onward). Incorporating land-use carbon debt increases the estimated 1.5°C overshoot attributed to high-income countries by ~87–114 GtCO₂, raising their total overshoot to ~812–885 GtCO₂, and shows that animal products contribute ~63% of the food-related debt while supplying ~17% of global calories. The chapter frames these results as a legacy responsibility indicator that persists until carbon stocks recover, and as a complementary lens for debates on equitable mitigation and carbon dioxide removal.
Taken together, the three studies highlight that deploying CDR in a responsible manner requires an integrated strategy encompassing the three pillars examined: diversification, systemic integration, and equity. First, a portfolio approach is essential: no single technology can safely achieve the billions of tonnes of removals needed, so a mix of methods must be pursued to balance feasibility, effectiveness, and co-benefits while hedging against the risks of any one approach. Second, systems thinking is crucial: CDR options should be planned in concert with broader sustainability transformations (like changes in agriculture and energy systems) to overcome resource bottlenecks and avoid simply shifting problems from one domain to another. Third, fairness must be a core design principle: the responsibility for removing carbon should align with those actors most responsible for emissions (past and present) and most capable of taking action, to uphold climate justice on the path to net-zero. Limitations of the research include, among others, uncertainties in future scenarios and global datasets, and the need for socio-political analysis beyond the scope of this thesis. Future work could integrate these technical findings with governance and public engagement strategies. All in all, the insights from this thesis provide a more solid analytical grounding for CDR policy. By answering what portfolio of CDR to deploy, how to implement it sustainably, and who should shoulder the responsibility, this work contributes to ensuring that CDR can safely help stabilize the climate. In sum, responsible removals, characterized by effectiveness, sustainability, and equity, offer a credible and ethical pathway to help meet our climate targets while minimizing the risks and trade-offs that uncritical CDR deployment would entail.