The Paris Agreement's goal of limiting global warming to well below 2°C, ideally 1.5°C, necessitates drastic reductions in CO2 emissions. The remaining carbon budget, the total allowable CO2 emissions to achieve these targets, is rapidly depleting. Current emission rates, around 42 GtCO2 per year, threaten to exhaust the 1.5°C budget by 2030. Exploiting all existing fossil fuel resources (nearly 11,000 GtCO2) is incompatible with these goals. This discrepancy has led to discussions on 'unburnable fuels' and the risk of stranded assets, prompting interest in supply-side climate policies, including production taxes, subsidy removal, and extraction moratoria. Several countries have initiated unilateral moratoria, and social movements actively target fossil fuel projects. Initiatives like Leave It in the Ground (LINGO) and Oil Change International have increased awareness. The International Energy Agency advocates for reduced fossil fuel investment and the retirement of existing projects. Selecting which resources remain unextracted is crucial for effective international systems. Ethical considerations suggest developed countries should bear more responsibility, while economic efficiency points to leaving resources with higher extraction costs untapped. This study departs from previous approaches by using socio-environmental impacts to suggest alternative unburnable fuel distributions. Previous global-scale assessments focused primarily on production costs, lacking spatially explicit allocations based on equity and socio-environmental factors. Local initiatives exist to protect resources in biodiverse areas, but a global, spatially explicit assessment is lacking. Fossil fuel extraction severely impacts biodiversity, human health, and human rights, providing further rationale for their conservation. This paper proposes a methodology to prioritize unburnable fossil fuel resources using socio-environmental criteria, focusing on conventional oil due to the high cost and impact of unconventional extraction.

Existing literature highlights the urgent need to reduce fossil fuel emissions to meet the Paris Agreement goals. Studies have estimated the remaining carbon budgets for limiting warming to 1.5°C and 2°C, emphasizing the rapid depletion of these budgets at current emission rates. The concept of 'unburnable fuels' or 'stranded assets' has gained prominence, underscoring the incompatibility of exploiting all existing fossil fuel resources with climate targets. Research has explored supply-side climate policies, including various regulatory and economic instruments aimed at limiting fossil fuel production. Studies have examined the ethical and economic considerations for allocating unburnable fossil fuels, with some focusing on the historical responsibility of developed countries and others on the economic efficiency of resource allocation. However, existing work often lacks the spatially explicit allocation of unburnable fossil fuels at the global level. Although previous studies have assessed the need to leave fossil fuels in the ground at a global scale, they have focused predominantly on cost-optimality and not on the crucial role that socio-environmental criteria can play in defining which specific resources need to be kept untapped. This work bridges this gap by proposing a methodology and implementing it to create a spatially explicit map of unburnable conventional oil.

This study utilizes a spatial assessment model to identify and prioritize unburnable conventional oil resources based on socio-environmental criteria. The model integrates georeferenced data on conventional oil resources from the United States Geological Survey (USGS), along with data on biodiversity hotspots, richness centers of endemic species (terrestrial and marine), protected areas (from the World Database on Protected Areas), urban areas (with a 10-km buffer), and territories of Indigenous Peoples in voluntary isolation. The study follows Welsby et al.'s (2021) estimate that 71% of conventional oil resources should remain unextracted by 2050 to limit warming to 1.5°C. Based on this, and using the USGS data, the study calculates that 1524 Gbbl of conventional oil resources need to remain untapped. The methodology involves two steps: 1) defining 'exclusion zones' where oil extraction is strictly off-limits due to overlapping with high-priority socio-environmental criteria; and 2) ranking remaining oil resources to identify additional resources to reach the 1524 Gbbl target, prioritizing areas with high biodiversity or high rural population density. The spatial analysis is conducted using Geographic Information Systems (GIS) software (QGIS, ArcGIS) to calculate overlaps between oil resources and the socio-environmental criteria. Three scenarios are developed for the second step: one based on rural population density (social criterion) and two based on terrestrial and marine endemic species richness (biological criteria). Data sources are predominantly open-access databases, including the USGS, FAO, UNEP-WCMC, CEPF, Conservation International, and Survival International.

The study's key findings center on the creation of a global atlas of unburnable conventional oil resources. Analysis reveals that 609 Gbbl of conventional oil resources overlap with the defined exclusion zones, which include areas such as biodiversity hotspots, protected areas, urban regions, and territories of Indigenous Peoples in voluntary isolation. These exclusion zones encompass a total area of approximately 29.5 million km². Significant portions of these resources are located in the Middle East, but the proportion of unburnable resources is highest in Developing Asia (excluding China and India), with approximately 78% of their resources falling within the unburnable category. Since 1524 Gbbl of conventional oil needs to remain untapped to meet the 1.5°C warming target, additional resources beyond those in the exclusion zones must be identified. Three scenarios for prioritizing these additional resources are presented: a social scenario based on rural population density, and two biological scenarios based on terrestrial and marine endemic species richness. The spatial distributions of these additional unburnable resources vary across scenarios, highlighting the trade-offs between social and ecological considerations. Table 1 provides a detailed breakdown of unburnable oil resources by socio-environmental criterion, and Table 2 shows the regional distribution of unburnable conventional oil resources within exclusion zones.

This research provides a spatially explicit framework for operationalizing supply-side climate policies, moving beyond previous cost-based approaches by incorporating socio-environmental considerations. The atlas of unburnable oil resources offers practical guidelines for energy corporations, governments, and investors to minimize the risk of stranded assets by identifying areas where oil extraction is incompatible with environmental and social priorities. The findings reinforce the strong case for leaving a substantial portion of oil resources untapped to limit warming to 1.5°C. Using socio-environmental criteria strengthens the collateral benefits of climate policies, generating additional co-benefits beyond climate mitigation. The study demonstrates the feasibility of entirely excluding extraction in highly sensitive areas while still meeting the overall unburnable oil target. The flexibility of the methodology allows for the inclusion of additional criteria, such as Indigenous Peoples' consent or the potential for environmental conflicts, further enhancing the policy relevance of this work.

This study presents a novel, spatially explicit atlas of unburnable conventional oil resources, integrating socio-environmental criteria to enhance the co-benefits of climate policies. The results highlight the substantial overlap between environmentally and socially sensitive areas and conventional oil resources, demonstrating the feasibility of prioritizing these areas for protection while meeting climate goals. The methodology is flexible and can be adapted to incorporate additional criteria and other fossil fuel types, providing a powerful tool for informing supply-side climate policies. Future research could focus on refining the spatial resolution of the data, incorporating additional socio-environmental criteria, and analyzing trade-offs between different criteria to further optimize the selection of unburnable resources.

The study acknowledges limitations related to data availability. The use of 'technically recoverable resources' instead of 'economically recoverable resources' might overestimate the amount of potentially extractable oil. The spatial resolution of the data, using geological provinces rather than individual oil fields or reservoirs, limits the precision of the analysis. While the study utilizes a range of open-access datasets, some data may contain inherent uncertainties or biases. The lack of readily available global data on Indigenous consent presents a limitation in fully incorporating this critical social consideration. Further research could address these limitations by employing higher-resolution data, incorporating additional socio-environmental factors, and enhancing the assessment of economic feasibility.