Isabela Butnar

Integrated assessment models (IAMs) are increasingly criticised as opaque and disconnected from the concerns of those affected by their results. Participatory and transdisciplinary approaches respond to this, but stakeholder input is often simplified, narrowed, or dropped once it meets a model's technical limitations, without explanation. This paper asks what happens when model tractability no longer filters which research questions (RQs) stakeholders can raise in the first place. Drawing on the Horizon Europe project DIAMOND, we describe a transdisciplinary process in which 40 RQs were co-designed with stakeholders across nine themes, eight scoped in advance and one that emerged unprompted, then triaged for tractability against six IAMs. In six of the nine themes, stakeholder input redirected or extended the project's initial framing rather than confirming it, and none of the 40 RQs was rated as requiring no model adjustment. Rather than treating these limitations as reasons to filter questions in advance, we argue that transparency about them should be an output of the process itself. Research questions IAMs cannot yet answer are documented and published as an open repository instead of being silently dropped, turning an unexamined gatekeeper into a visible, contestable record of whose futures still need modelling.

Carbon dioxide removal (CDR) will be required to support rapid emission reductions and reach net zero emissions. Recent studies have highlighted different global warming impacts of CDR options depending on the durability of their carbon storage. Geological net zero, which demands that residual fossil CO2 emissions are matched by permanent geological storage of CO2, has been identified as one potential policy approach to address these durability differences, as it recognizes the warming risk of delayed CO2 release from less permanent storage. Considering the UK as a national case study, we investigate the effect a geological net zero policy may have on national climate change mitigation strategies. Using the national-scale energy system model UK TIMES, we explore different ways of implementing a geological net zero policy: a strict implementation applied on an annual accounting basis from 2030 forward, a progressive implementation that introduces a more gradual “share” of fossil emissions covered under the policy, and a cumulative implementation to 2050 which allows emissions earlier in the time horizon to be compensated for later. Our initial results suggest extreme difficulty in achieving GNZ, highlighting that the UK is unlikely to be able to able to reach geological net zero before 2040, as more than one decade is required to decarbonize the emitting sectors and significantly scale up removal methods with permanent storage. It is also clear that the speed of change required to achieve even this outcome is significant, requiring rapid and deep phase out of fossil fuel use much earlier than traditional scenarios suggest. We find, however, that progressive and cumulative GNZ implementations can get much closer to solving, and offer more ambitious pathways that significantly reduce the UK's cumulative emissions to 2050 compared to the current UK pathways and emissions targets. We quantify residual emissions and determine the sectors with the highest challenges for full decarbonization and find that the availability of key resource biomass as well as the pace of scaling up carbon capture and storage infrastructure have crucial impact on the feasibility of any geological net zero policy.To our knowledge, this study is the first to assess potential geological net zero policies at national level, providing insights into the opportunities and challenges of faster decarbonization and dependence on geological carbon storage in all sectors of the UK economy. Findings of this study are also relevant for other nations considering more ambitious climate change mitigation policy.

Carbon dioxide removal (CDR) is essential for achieving net zero and net-negative emissions, yet robust monitoring, reporting, and verification (MRV) remains a major challenge. Current accounting practices are fragmented, with inconsistent system boundaries and a narrow focus on carbon, overlooking wider environmental impacts and co-benefits. Drawing on five years of research and demonstration under the UK GGR-D Programme, the most long-term global MRV effort, with multiple years of monitoring across multiple CDR technologies, this study proposes a harmonized framework for defining system boundaries across six key CDR approaches: biochar, bioenergy with carbon capture and storage (BECCS), direct air capture with storage (DACCS), peatland restoration, enhanced rock weathering, and afforestation. We map data availability for evidencing net removal across full supply chains, including the capture of CO2 from the atmosphere and its final storage, and assess gaps in environmental impact data. Our findings show that harmonization is feasible across diverse CDR methods—land-based, engineered, and hybrid land-based - engineered—but data coverage is uneven, particularly for non-carbon metrics. These gaps pose risks for sustainability assessments and the credibility of CDR claims, with implications for emerging policy frameworks and carbon markets. This work provides actionable insights for developing robust MRV systems that support transparent, sustainable CDR deployment at scale.

Passenger car carbon footprints are highly sensitive to future energy systems, a factor often overlooked in life cycle assessment. We use a time-dependent prospective life cycle assessment to enhance carbon footprints under four 1.5–3.0 °C decarbonisation pathways for electricity, fuel, and hydrogen from an energy-based integrated assessment model. Across 5000 comparative cases, battery electric vehicles consistently have the lowest carbon footprints compared to hybrid, plug-in hybrid, and fuel-cell vehicles. For example, battery electric vehicles show an average 32 to 47% lower footprint than hybrid combustion in 3.0 °C and 1.5 °C climate-compatible futures, respectively. This is driven by greater projected decarbonisation of electricity compared to fossil-dominated fuels and hydrogen. Battery electric vehicles meaningfully retain their advantage for mileages over 100,000 km, even in regions with carbon-intensive electricity since these are anticipated to decarbonise the most. Although our study supports battery electric vehicles as the most reliable climate-mitigation option for passenger cars, reducing their high manufacturing footprint remains important.

Life Cycle Assessment (LCA) methods are increasingly used for policy decision‐making in the context of identifying and scaling up sustainable carbon dioxide removal (CDR) interventions. This article critically reviews CDR LCA case‐studies through three key lenses relevant to policy decision‐making on sustainable CDR scale‐up, namely comparability across CDR assessments, assessment of the climatic merit of a CDR intervention, and consideration of wider CDR co‐benefits and impacts. Our results show that while providing valuable life cycle understanding, current practices utilize diverse methods, usually attributional in nature, which are CDR and time‐specific. As a result, they do not allow comprehensive cross‐comparison between CDRs, nor reveal the potential consequences of scaling up CDRs in the future. We suggest CDR LCA design requires clearer definitions of the study scope and goal, the use of more consistent functional units, greater comprehensiveness in system boundaries, and explicit baseline definitions. This would allow for robust assessments, facilitating comparison with other CDR methods, and better evidencing net climate benefits. The inventory should collect time‐dependent data on the full CDR life cycle and baseline, and report background assumptions. The impact assessment phase should evidence the climatic merits, co‐benefits, and trade‐offs potentially caused by the expanding CDR. Finally, to ensure a sustainable scale‐up of CDR, consequential analyses should be performed, and interpretation involves the comparison of all selected metrics and the permanence of carbon storage against a baseline scenario.

Scientific research pushes forward the boundaries of human knowledge, but often at a sizable environmental cost. The reliance of researchers on single-use plastics and disposable consumables has come under increased scrutiny as decarbonisation and environmental sustainability have become a growing priority. However, there has been very little exploration of the contribution of laboratory consumables to ‘greenhouse gas’ (GHG) carbon emissions. Carbon footprint exercises, if capturing consumables at all, typically rely on analyses of inventory spend which broadly aggregate plastic and chemical products, providing inaccurate data and thus limited insight as to how changes to procurement can reduce emissions.This paper documents the first effort to quantify the carbon footprint of common, single-use lab consumables through emission factors derived from life cycle assessments (LCAs). A literature review of LCAs was conducted to develop emission factors for lab consumables, considering the emission hotspots along each product’s life cycle to identify where emission reduction policies can be most effective. Results can be used as inputs for lab practitioners seeking to understand and mitigate their carbon footprint.