Human and planetary health implications of negative emissions technologies

Limiting global warming to 1.5 °C likely requires large-scale carbon dioxide removal (CDR), potentially up to ~1,000 Gt CO₂ by 2100. While Direct Air Carbon Capture and Storage (DACCS) and Bioenergy with Carbon Capture and Storage (BECCS) are among the most prominent NETs, it remains unclear whether their societal and planetary benefits outweigh potential harms when deployed at scale. Prior work has largely emphasized costs and CDR potentials, with fewer efforts examining side-effects and co-benefits beyond climate change or benchmarking against Earth’s biophysical limits (Planetary Boundaries). A comprehensive assessment integrating both human health and planetary health implications of DACCS and BECCS is missing. This study addresses that gap by quantifying human health impacts in Disability-Adjusted Life Years (DALYs) and planetary impacts across seven Earth-system processes, to reveal co-benefits, trade-offs, and conditions under which NETs can advance climate targets without compromising other sustainability dimensions.

Previous assessments of DACCS and BECCS focused on techno-economics and CDR potentials, often overlooking broader health and environmental side-effects (e.g., Minx et al., Fuss et al., Keith et al., Realmonte et al., Marcucci et al.). Life cycle studies exist but are challenging to interpret in absolute sustainability terms. Only recently have BECCS impacts been compared to Planetary Boundaries, highlighting potential conflicts with biosphere integrity and biogeochemical flows (Heck et al.). Environmental co-benefits and trade-offs commonly arise in energy transitions, suggesting possible tensions for NETs. This work builds on LCA methods (ReCiPe 2016), updates climate-health damage factors (Tang et al.), and PB-linked impact assessment (Ryberg et al., Galán-Martín et al.) to evaluate NETs in an absolute sustainability context.

Study design and scenarios: Sixteen scenarios delivering 5.9 Gt/year net CO₂ removal from 2030 to 2100 were modeled, aligned with SSP2-1.9 (excluding AFOLU CDR). Scenarios vary by NET type, energy/biomass sources, and CO₂ storage routes: ten DACCS (HTLS-DACCS and LTSS-DACCS) powered by geothermal (excess heat), wind, PV, nuclear, NG+CCS, or the SSP2-1.9 grid; four BECCS configurations generating electricity (displacing SSP2-1.9 grid) using Miscanthus (rainfed, with soil carbon sequestration) or Poplar (irrigated, with land-use change emissions); two hybrid configurations (BEDACCS) coupling BECCS steam/electricity with LTSS-DACCS. CO₂ storage options include geological sequestration (high pressure), in situ mineral carbonation using freshwater or seawater, and ex situ mineral carbonation (the latter not applied to DACCS due to heat requirements). Unless specified, reported impacts average across in situ storage options. Functional unit and LCA approach: The functional unit is net removal of 5.9 Gt CO₂/year. An attributional LCA was used with background processes reflecting average market mixes (Ecoinvent 3.5). For BECCS multi-functionality, system expansion credits displacement of SSP2-1.9 grid electricity and, for ex situ mineralization, substitution of beneficiated iron ore and sand. The impacts to achieve the functional unit were scaled by CDR efficiency (ηCO₂ = (captured CO₂ − life-cycle CO₂ emissions)/captured CO₂). Models were implemented in SimaPro 9.2 using generic (non-spatial) data. Human health assessment: Health impacts were quantified in DALYs using ReCiPe 2016 endpoint (Hierarchist) over a 100-year horizon for non-climate mechanisms (fine particulate matter formation, tropospheric ozone formation, human carcinogenic and non-carcinogenic toxicity, water consumption, stratospheric ozone depletion, ionizing radiation). Climate-related health damages were calculated using spatially resolved damage factors (Tang et al.) for SSP2, covering undernutrition, malaria, coastal floods, diarrhea, heat stress, and dengue, apportioned to aggregated world regions. Population projections follow SSP2. Health externalities were monetized using a standard conversion (1 DALY ≈ €74,000 in 2003 euros). Planetary Boundaries assessment: Impacts on seven Earth-system processes were quantified relative to the Safe Operating Space (SOS): climate change (CO₂ concentration, energy imbalance), ocean acidification, terrestrial biosphere integrity, biogeochemical flows (N, P), global freshwater use, stratospheric ozone depletion, and land-system change. Characterization mainly follows Ryberg et al. (300-year horizon for climate and ocean acidification), complemented by Galán-Martín et al. For biosphere integrity, impacts were estimated from greenhouse gas emissions and land use using mean species abundance-based factors, with the PB expressed as a 10% decrease (mapped to mean species abundance). Results are reported as percentages of SOS. The baseline scenario (scenario 0) represents emitting 5.9 Gt/year CO₂ (i.e., SSP2-1.9 without NETs), resulting in +0.19 °C [0.11–0.26] relative to SSP2-1.9 by 2100. Key assumptions and exclusions: Prevented impacts from CO₂ removal are assumed equal in magnitude to impacts from emitting the same CO₂ amount. Potential weakening of carbon sinks under net-negative emissions is noted but not modeled. Infrastructure impacts for NETs are omitted due to data gaps; prior work suggests relatively small contributions versus operational life-cycle impacts.

Health impacts and co-benefits: Without NETs (scenario 0; +0.19 °C), the additional burden is on the order of 9–10² DALYs per million people per year, comparable to prostate cancer. Deploying NETs yields net health gains in 15 of 16 scenarios, ranging roughly from 2–10² to 9–10² DALYs per million per year relative to the baseline; top scenarios approach the 2019 global burden of prostate cancer, with many comparable to Parkinson’s disease. Monetized health co-benefits span 35–148 US$/t CO₂ captured, comparable to levelized costs of scaled BECCS (134–188 US$/t) and HTLS-DACCS (121–249 US$/t). Scenario rankings and drivers: BECCSO-MISC (Miscanthus, soil carbon sequestration) performs best for health; BEDACCS-MISC, and HTLS-DACCS powered by wind or nuclear also rank highly. LTSS-DACCS using geothermal excess heat fares well among LTSS; LTSS-DACCS powered by PV performs worst among DACCS due to particulate matter from PV panel production. Ex situ mineralization is the most damaging storage option for health; in situ mineralization using seawater shows the lowest health impacts among storage routes. In BECCS, displacement of grid electricity is a key health benefit; removing electricity credits reduces BECCSO-MISC and BECCSO-POP avoided impacts by 9% and 26%, respectively. Fine particulate matter formation is the dominant regional health contributor (>44%) in most scenarios; irrigation water use dominates in poplar-based BECCS (50% in BECCSO-POP, 47% in BEDACCS-POP). Toxicity impacts in poplar BECCS arise largely from heavy metal leaching in plantations and fly ash disposal; Miscanthus BECCS can avoid some toxicity impacts due to metal retention in biomass. Regional distribution of climate-health co-benefits: For a representative DACCS case (HTLS-DACCS with wind and seawater mineralization), 98% of avoided climate-sensitive DALYs accrue to Africa and Asia, with more than half in Sub-Saharan Africa. Breakdown of avoided climate-related DALYs: 70% undernutrition, 15% malaria, 9% coastal floods, 5% diarrhea, 2% heat stress. On a per capita basis, Sub-Saharan Africa benefits most; North America, Europe, and Russia benefit least due to lower sensitivity to climate-amplified health risks. Planetary Boundaries outcomes: The baseline (no NETs) imposes climate change impacts >200% of the climate SOS and 70% of the ocean acidification SOS, and 12% of biosphere integrity SOS (over a 300-year horizon). NETs can avoid impacts equivalent to 204–229% (climate change) and 70–73% (ocean acidification) of SOS relative to the baseline. DACCS scenarios (especially LTSS with renewables and HTLS) have low planetary impacts and can avert 8–12% of biosphere integrity impacts relative to baseline. By contrast, BECCS imposes net damage to terrestrial biosphere integrity (exceeding the baseline by up to 16% of SOS) due to land-use pressures, and creates higher pressures on biogeochemical N flows and freshwater use. Only DACCS prevents damage to biosphere integrity while keeping all other Earth-system impacts within a small fraction of the SOS (≤~2% per process, depending on configuration).

The study demonstrates that large-scale CDR via DACCS and BECCS can yield substantial human health co-benefits, offsetting non-climate life-cycle health burdens and achieving net health gains comparable to major global diseases. These benefits are unevenly distributed, overwhelmingly favoring regions most vulnerable to climate-sensitive health risks (Africa and Asia). From a planetary perspective, both NETs help remain within climate- and ocean-related boundaries by counteracting historic emissions; however, BECCS poses significant trade-offs—especially land-system and biosphere integrity impacts, nitrogen flows, and freshwater use—while DACCS offers a more favorable environmental profile with minimal pressure on other Earth-system processes. These insights indicate that while emissions reductions must remain the priority, DACCS can be a complementary tool to address hard-to-abate emissions with relatively limited side-effects, and BECCS may be beneficial when biomass sources and locations minimize irrigation and land-use impacts (e.g., rainfed Miscanthus on suitable lands). The quantified health externalities provide an additional economic incentive for NET deployment, potentially improving cost-effectiveness when co-benefits are internalized. Policy implications include setting separate targets for emissions reductions and CDR to avoid mitigation deterrence, aligning NET strategies with SDGs (co-benefits for SDG3 and SDG2; potential tensions with SDG6 and SDG15), and adopting regionally tailored portfolios that leverage local energy, land, and water conditions.

This work provides an integrated, absolute-sustainability assessment of DACCS and BECCS, quantifying long-term human health and planetary health implications of removing 5.9 Gt CO₂/year under SSP2-1.9. NETs deliver significant global health co-benefits—monetarily meaningful and comparable to levelized costs—while reducing pressures on climate and ocean acidification. DACCS emerges as environmentally superior, capable of averting damage to terrestrial biosphere integrity without challenging other planetary boundaries, whereas BECCS performance is highly contingent on biomass choice and management, with rainfed Miscanthus outperforming irrigated poplar. The results support NETs as part of a broader mitigation portfolio, with careful design to minimize regional health burdens and planetary trade-offs. Future research should develop regionalized, spatially explicit assessments, incorporate infrastructure and supply chain impacts, expand indicators (e.g., SDG7 and SDG14), and evaluate alternative biomass strategies and storage pathways to optimize NET roadmaps within planetary limits.

Key limitations include: use of generic, non-spatial life-cycle inventory data (Ecoinvent 3.5), precluding detailed geographic differentiation for non-climate health impacts; omission of NET infrastructure construction and decommissioning due to data gaps (likely minor but unquantified); assumption that avoided impacts from CO₂ removal equal the impacts of emitting the same amount, despite potential weakening of natural carbon sinks under net-negative emissions; health impact characterization over a 100-year horizon (non-climate) and planetary climate/ocean assessments over 300 years, which influence temporal attribution; omission of freshwater and marine biosphere integrity impacts due to lack of suitable methods; and reliance on system expansion credits for BECCS electricity and ex situ byproducts, which affect comparative results. NET location is not specified, yet siting strongly influences regional health outcomes (e.g., particulate matter exposure, water scarcity).