Geo-engineering - The Sustainability Management Wiki

Authors: Muhammad Khuzaim Khan, Marinda Febri
Edited by: –
Last updated: May 17, 2026

Executive summary

Geoengineering refers to deliberate, large-scale interventions in the Earth system intended to limit climate risks. In practice, the field divides into carbon dioxide removal (CDR), which lowers atmospheric CO₂ by strengthening natural or engineered sinks, and solar radiation modification (SRM), which reflects a small fraction of sunlight to reduce warming. CDR addresses the root cause of warming but requires substantial energy, land, water, and infrastructure. SRM can cool the planet quickly at comparatively low direct financial cost, but it does not reduce CO₂ concentrations or ocean acidification and creates significant systemic and governance risks.

For organizations, CDR resembles other decarbonization investments: it can be planned, measured, and integrated into net-zero strategies, but it faces material constraints, cost uncertainty, and nontrivial environmental and social trade-offs. Nature-based options (afforestation, reforestation, soil carbon) can provide biodiversity and livelihood co-benefits when implemented well, yet they face permanence risks and site-specific climate effects such as albedo changes. Engineered options (DACCS, BECCS, enhanced weathering) offer more controllable accounting pathways and potentially higher permanence, but they depend on low-carbon energy, CO₂ transport and storage networks, and careful management of land use, water, and pollution risks. A diversified portfolio generally reduces per-ton impacts compared with reliance on any single approach.

SRM options such as stratospheric aerosol injection and marine cloud brightening remain largely in the research phase. While models suggest SRM could reduce temperatures rapidly, they also indicate uneven regional impacts (especially on precipitation) and the possibility of severe “termination shock” if deployment stops abruptly while greenhouse gas concentrations remain high. These characteristics make SRM primarily a governance challenge: they raise questions about legitimacy, liability, monitoring, and decision-making across borders, and they could intensify geopolitical and distributional conflicts over desired climate outcomes.

Current policy and regulation treat CDR and SRM asymmetrically. Binding international rules remain limited, and national approaches diverge, with some jurisdictions promoting CDR certification while taking a precautionary stance toward SRM. Organizational leaders should prioritize rapid emissions reductions, treat CDR as a complementary tool for residual emissions and potential overshoot management, and track evolving standards for measurement, reporting, and verification. Engagement on SRM should focus on risk governance, transparency, and support for responsible research norms rather than near-term deployment.

1 Description & mechanism

1.1 Carbon Dioxide Removal (CDR)

Carbon Dioxide Removal (CDR) technologies aim to reduce atmospheric CO₂ concentrations by artificially increasing the capacity and uptake rate of carbon sinks.¹ Unlike conventional mitigation, which prevents emissions at the source, CDR actively removes CO₂ from the ambient atmosphere after emissions have occurred.²

CDR technologies and mechanisms:

a. Bioenergy with Carbon Capture and Storage (BECCS) combines biomass cultivation with carbon sequestration. This technology captures carbon in plant biomass through photosynthesis, subsequently combusts the organic material for energy production, and captures and sequesters the resulting CO₂ in geological storage sites such as aquifers, coal beds, or depleted oil and gas fields.¹ ³ BECCS provides both carbon removal and energy production, making it attractive for integrated energy-climate strategies.

b. Direct Air Carbon Capture and Storage (DACCS) employs chemical sorbents, such as alkaline liquids, exposed to ambient air to remove CO₂.¹ The primary constituent cost is the carbon-free energy required to power these machines, which must overcome the thermodynamic barrier of capturing CO₂ at dilute ambient concentrations of approximately 0.04%.² Current DACCS systems require 1500-10,000 MJ/t(CO₂) for separation, well above the theoretical minimum of ~500 MJ/t(CO₂).²

c. Enhanced Weathering accelerates natural carbonate or silicate reactions that sequester atmospheric CO₂ over millennial timescales by grinding rocks and dispersing them over large surface areas.¹ ² This approach uses geochemical principles to increase reaction rates and store weathering products on land or in the ocean through ocean alkalinization.

d. Afforestation and Reforestation leverage photosynthesis to capture CO₂ in tree biomass and soil carbon.² Principally, the carbon storage potential is large; historical deforestation released 2,400±1,000 Gt(CO₂).² However, realistic estimates range from 4-12 Gt(CO₂)/yr by 2100, limited by land-use competition with agriculture and livestock production.²

1.2 Solar Radiation Modification (SRM)

Solar Radiation Modification (SRM) counteracts the warming effects of anthropogenic greenhouse gases by deflecting sunlight back into space before it can be absorbed by Earth, thereby offsetting global-scale warming.¹ ⁴ Approximately 30% of incoming solar radiation is reflected to space; SRM aims to increase this fraction to cool the planet.¹

SRM technologies and mechanisms:

a. Stratospheric Aerosol Injection (SAI) represents the most technically and economically feasible near-term SRM approach.¹ ⁴ ⁵ Inspired by volcanic eruptions that periodically reduce global temperatures, SAI would inject sulfate aerosol precursors into the stratosphere at altitudes of 15-25 km.¹ ⁵ The stratosphere’s convective stability allows injected particles to remain for 1-2 years, reflecting light to space, compared to the few days they reside in the lower atmosphere.¹ ⁴

The most likely implementation approach involves high-flying aircraft outfitted with aerosol precursor-dispensing systems.⁵ Sulfur dioxide (SO₂) would oxidize to SO₃ over approximately one month, then quickly react with water to form sulfuric acid aerosols.⁴ Alternative materials include calcium carbonate, diamond, and alumina, which would reduce stratospheric heating and ozone impacts but face technical challenges in achieving proper dispersion without rapid coagulation.⁴

b. Marine Cloud Brightening (MCB) / Marine Sky Brightening (MSB) exploits the Twomey effect, whereby adding small particles into low-lying clouds over oceans creates more small cloud droplets that are more reflective.¹ ⁴ Implementation would require constructing a fleet of ships to spray salt or fine particles into the lower atmosphere over amenable ocean areas.¹ Unlike SAI, these particles are short-lived and require continuous deployment to sustain their effect.¹

1.3 Historical background and diffusion

Climate geoengineering concepts have evolved over six decades, from early theoretical proposals to current research programs.

Early development (1960s–2000): The idea of modifying Earth’s albedo to reduce warming emerged in the 1960s, inspired by cooling effects from volcanic eruptions.⁴ Albedo modification was the only climate response in the first US presidential report on climate change (1965).⁴ Stratospheric aerosol injection was proposed in the early 1970s.⁴ When climate became a policy issue in the late 1980s, only emissions reduction was considered [4]. The term “geoengineering” gained attention gradually as recognition grew that emissions cuts alone were insufficient.⁴ Adaptation emerged as a complementary response in the mid-1990s, while carbon dioxide removal (CDR) gained prominence from the early 2010s onward.⁴ CDR became increasingly central to climate policy as integrated assessment models showed that limiting warming to 2°C would require large-scale negative emissions.² ⁶ The widely used RCP.⁷ scenario, which informs IPCC assessments, assumes extensive deployment of CDR technologies, particularly BECCS, to achieve net-negative emissions in the second half of this century.² Analysis of 116 scenarios consistent with 2°C warming found that 87% require a transition to global net negative emissions, highlighting CDR’s assumed role in achieving climate targets.²

Crutzen’s catalyst (2006): In 2006, Nobel laureate Paul Crutzen argued that SRM research was necessary despite environmental risks.⁴ His essay sparked widespread debate and led to multiple scientific assessments.⁴ However, opposition emerged from scientists and NGOs who argued that research could lead to premature deployment.⁴

Recent acceleration (2020–present): Climate geoengineering research has expanded significantly since 2020 [4]. The 2023 Climate Overshoot Commission recommended SRM research alongside a moratorium on large-scale deployment.⁴ The World Climate Research Programme adopted climate intervention as a research initiative in October 2023.⁴

Table 1: Historical timeline and current development status of major climate engineering technologies⁴⁸

Technology Type

First Proposed

Research Phase

Current Status (2024)

SAI

Early 1970s

Active modeling

Pre-deployment R&D

MCB

2000s

Laboratory trials

Technology development

DACCS

1990s

Pilot facilities

Early commercial

BECCS

1990s

Demonstration

Limited deployment

Enhanced Weathering

2000s

Field trials

Research phase

2 Economic performance

Economic assessments reveal a sharp contrast between CDR, SRM, and conventional mitigation, with SRM appearing extremely cheap but risky, and CDR costly but structurally similar to mitigation in both effects and incentives.¹ ² ³ ⁵ ⁶ ⁸

2.1 Cost comparison: CDR, SRM, and mitigation

CDR and mitigation both act on atmospheric CO₂ and therefore deliver “root-cause” climate benefits; economically, they behave as near-perfect substitutes.¹ ³ ⁶ In contrast, SRM only masks warming by altering Earth’s radiative balance and leaves CO₂ concentrations—and their impacts, such as ocean acidification—largely unchanged.¹ ² ⁴ ⁶

For SRM, cost estimates are strikingly low. SAI based on purpose-built high-altitude aircraft could offset a substantial fraction of anthropogenic radiative forcing for on the order of 1–10 billion USD per year, or less than 0.1% of world GDP.¹ ⁵ ⁶ Smith and Wagner’s engineering analysis for a dedicated “SAI Lofter” fleet project’s average operating expenses of about 2.25 billion USD per year over the first 15 years, with development costs of 3.5 billion USD and deployment of roughly 1 Mt of sulfur annually by the early 2040s in a scenario targeting 0.25 W/m² of forcing reduction.⁵

For CDR options span a broad, generally high-cost range, comparable to or exceeding ambitious mitigation pathways.¹ ² ³ ⁶ ⁸ For DACCS, current estimates cluster around 600–1,000 USD/tCO₂, with optimistic learning-curve projections aiming for 100–300 USD/tCO₂ by mid-century.¹ ² ⁸ BECCS costs range from about 100 to 300 USD/tCO₂ under plausible large-scale deployment.¹ ² ³ ⁸ Enhanced weathering and afforestation are usually priced at 50–200 USD/tCO₂, but are constrained by mining, land, and ecological limits.¹ ² ⁶ ⁸

From a policy perspective, the optimal carbon price equals the marginal cost of the last unit of CO₂ abated or removed.³ ⁶. This means that CDR’s marginal cost schedule effectively pins down the socially optimal long-run carbon price, making CDR economically equivalent to conventional mitigation.¹ ³ ⁶ In contrast, SRM’s cost per unit of temperature reduction is two to three orders of magnitude lower, making it unique in both price and risk profile and incentive structure.¹ ⁵ ⁶

2.1 Cost-risk asymmetry of SRM vs. CDR

The combination of low monetary cost, rapid temperature response, and imperfect climatic compensation produces a pronounced cost-risk asymmetry between SRM and CDR.¹ ⁴ ⁶. For SAI, model studies suggest that deployment could reduce global mean temperature within a year or two of ramp-up, a timescale far shorter than that required for CO₂ concentration reductions via mitigation or CDR.² ⁴ ⁶ Yet the resulting climate would not simply revert to a lower-CO₂ state; spatial patterns of temperature, precipitation, and circulation would differ from those of any mitigation-only pathway because the forcing mix (high long-lived CO₂, lower shortwave radiation) is physically distinct.² ⁴ ⁶

This asymmetry has several consequences. First, SRM could in principle be undertaken unilaterally by a single nation or small coalition, because the direct financial costs are well within the budgets of many states.¹ ⁴ ⁶ Second, because SRM modifies climate without reducing CO₂, it creates a termination problem: if a large SAI program were suddenly stopped while greenhouse gas concentrations remained high, global temperatures would rapidly “catch up” to the latent warming implied by accumulated CO₂.² ⁴ ⁶ Modeling work shows that such termination shocks could generate warming rates multiple times larger than those under any realistic mitigation-only baseline, posing severe challenges for ecosystems and human systems adapted to slower change.² ⁶

By contrast, CDR is expensive and slow but risk-aligned with mitigation: it gradually lowers atmospheric CO₂, thereby reducing both temperature and non-temperature CO₂ impacts in a way that is more predictable and easier to integrate into existing policy frameworks.¹ ² ³ ⁶ Edenhofer et al. show that when CDR is available at costs comparable to abatement, optimal climate policy uses a combination of both instruments and treats removal as a flexible tool for managing overshoot and adjusting to uncertainty in damages and mitigation costs.³

Game-theoretic analyses indicate that CDR can slightly improve international cooperation relative to mitigation alone, especially when removal costs fall below abatement costs and when supply-side leakage via fossil fuel price channels is important.³ Heutel et al. and Franks et al. show that subsidizing removals can reduce leakage compared to a pure carbon tax regime, because removals do not directly depress fossil fuel producer prices in the same way as demand-side abatement.¹ ³ This cooperation-enhancing role stands in contrast to SRM, which may exacerbate distributional conflicts over preferred temperature targets and regional climate outcomes.¹ ⁴ ⁶

2.3 Industry development and cost trajectories

The emerging industry around climate engineering reflects these economic fundamentals: CDR is slowly building a large, capital-intensive sector, while SRM remains technically feasible but politically stalled.³ ⁴ ⁵ ⁸

CDR deployment today is dominated by conventional land-based practices. Afforestation, reforestation, and soil carbon measures currently deliver roughly 2 Gt(CO₂)/year of removal, while engineered approaches such as DACCS and BECCS together contribute far less than 0.01 Gt(CO₂)/year.³ ⁸ State of CDR assessments emphasize that reaching climate-relevant scales, several Gt(CO₂)/year by mid-century and potentially 10 Gt(CO₂)/year thereafter, would require a massive build-out of biomass supply chains, CO₂ transport and storage networks, and low-carbon energy infrastructure.² ³ ⁸ Order-of-magnitude estimates suggest cumulative investments of 1–3 trillion USD over 25 years, geological storage capacity comparable to the current global oil and gas industry, hundreds of millions of hectares of land for BECCS feedstocks, and energy inputs for DACCS that could reach 20–100% of present global electricity generation if operated at the upper end of proposed scales.² ³ ⁸

Despite these daunting requirements, CDR technologies exhibit learning rates comparable to those of other clean technologies. Experience curves for DACCS, BECCS, and related processes imply cost reductions of roughly 10–20% per doubling of cumulative deployment, analogous to observed patterns in solar PV, wind power, and batteries.¹ ³ ⁸ Smith et al. argue that with sustained R&D support and policy-driven demand, DACCS costs could plausibly fall into the 100–300 USD/t(CO₂) range, while BECCS and enhanced weathering could converge towards 50–150 USD/t(CO₂) by mid-century, though these projections remain uncertain and contingent on managing land, water, and social constraints.² ³ ⁸

For SRM, engineering analyses indicate that technical barriers are comparatively modest. The SAIL concept illustrates that a dedicated fleet of specialized aircraft could be designed, built, and deployed within roughly a decade, with total program costs on the order of tens of billions of dollars over 15 years, less than global annual spending on a single large energy technology class.⁴ ⁵ However, there is no emerging commercial “SRM industry” in the usual sense because deployment faces strong normative, legal, and governance objections, and because the service it provides, global temperature control, is a pure international public good with highly contested legitimacy and distributional consequences.⁴ ⁶

Table 2: Comparative resource requirements for climate-relevant CDR and SRM deployment²⁵⁸

Requirement

CDR (10 Gt(CO₂)/yr)

SRM (0.25 W/m²)

Ratio

Total Investment

$50-70 trillion (to 2100)

$36 billion/15 years

28-83:1

Annual Cost

$0.5-1 trillion/yr

$2.25 billion/yr

18-53:1

Energy Required

20-100% global electricity

Minimal

100:1

Time to Effect

20-50 years

1-2 years

10-50:1

In sum, economic performance reinforces a functional division between CDR and SRM. CDR is expensive, slow, and infrastructure-heavy, but integrates naturally with mitigation to manage CO₂ stocks and overshoot within familiar policy architectures.¹ ² ³ ⁶ ⁸ SRM offers a uniquely cheap and fast lever on global temperature, yet carries systemic climatic and geopolitical risks that current institutions are ill-equipped to manage, making its low cost as much a governance challenge as an economic advantage.¹ ⁴ ⁵ ⁶

3 Ecological performance

Geoengineering technologies, including Carbon Dioxide Removal (CDR) and Solar Radiation Management (SRM), have fundamentally distinct ecological profiles. CDR encompasses methods that extract CO₂ from the atmosphere for long-term storage in various reserves⁶⁹, while SRM involves techniques that enhance the Earth’s albedo or modify clouds to cool the surface.⁹ CDR directly reduces greenhouse gas concentrations but demands significant resources, affecting land, water, infrastructure, and biodiversity.¹⁰ In contrast, SRM can lower temperatures quickly, but it does not reduce CO₂ levels or ocean acidification, potentially disrupting weather patterns and ecosystems.⁹ This section assesses the ecological performance of both approaches through life-cycle assessments and empirical evidence.

3.1 CDR: Carbon removal potential and effectiveness

The ecological performance of CDR varies markedly across its four principal approaches: Bioenergy with Carbon Capture and Storage (BECCS), Direct Air Carbon Capture and Storage (DACCS), afforestation and reforestation, and enhanced weathering, all of which differ in their land, water, and energy footprints per tonne of CO₂ removed. The IPCC AR6 Report emphasizes that while CDR is essential in all modeled scenarios limiting global warming to 1.5-2°C, but cannot substitute for immediate emissions reductions.¹¹

BECCS: combines biomass energy production with geological CO₂ storage, with an estimated sustainable global potential of 0.5-5 GtCO₂/yr by 2050.¹⁹ However, as detailed in Section 2.3, meeting 2°C-consistent targets through BECCS alone would require 380 – 700 million hectares (Mha) of land area for bioenergy production (amounting to 25 – 46 % of the arable and permanent crop area) with associated food-price and water-stress consequences that will prove to be severe for the global South.¹² ¹³ ¹⁴ Heck et al. concluded that large-scale BECCS would potentially violate several planetary boundaries, for biosphere integrity, land-system change, and biogeochemical flows, causing an irreversible effect on Earth.¹⁴ Hanssen et al. found that sequestering 0.5-5 GtCO₂/yr with lignocellulosic BECCS would drive the extinction of tens of vertebrate species.¹⁵.

DACCS: presents a contrasting profile, with its ecological performance relating primarily to resource intensity rather than direct ecosystem disruption. For the removal of 1 GtCO₂/yr, DACCS requires approximately 2000 km2 of land, including solar photovoltaic supply, orders of magnitude smaller than BECCS or afforestation.¹⁶ Cobo et al. found that only DACCS can avert damage to the biosphere integrity without challenging other biophysical limits, with environmental impacts staying within 2% of safe operating space.¹⁷ The most dominant constraint is energy: global scale deployment could require up to 300 EJ/yr of energy input by 2100⁷⁰, with net removal efficiency falling as low as 9% when powered by fossil fuels.¹⁸

Afforestation and reforestation: offer a global potential of approximately 0.5–12 GtCO₂/yr, with co-benefits for biodiversity, soil conservation, and water quality when implemented on degraded lands with native species.¹⁹ However, a 2025 study by Riley et al. across 172 projects found that more than 10% may have their climate benefits entirely negated by albedo effects, while 25% may see their benefits halved.²⁰ Critically, Riley et al. also proposed an alternative, tiered approach for incorporating albedo considerations into carbon crediting protocols, from project-siting guidance to albedo-based discounts on credit volumes; a finding with direct implications for the CDR certification frameworks discussed in Section 5.2.²⁰ Carbon permanence remains a concern, as storage is vulnerable to wildfire, droughts, pest outbreaks, and land-use change, leading to an effective storage far shorter than the millennial timescale of geological storage.²¹

Enhanced weathering: spreads crushed silicates on agricultural lands, converting atmospheric CO₂ to stable bicarbonate ions via chemical dissolution, without requiring dedicated land for implementation, and also potentially improving crop yield.²² Field trials in the US corn belt showed cumulative removal of 10.5 ± 3.8 tCO₂/ha with 12 – 16% increased maize and soybean yields.⁷¹ Though the choice of mineral governs heavy metal accumulation, with basalt recommended to prevent significant terrestrial and environmental impact.²³

A consistent finding emerges across all CDR approaches that there is no single technological approach that can sustainably deliver the gigatonne-scale removal required under Paris-consistent pathways.¹⁹ A diversified portfolio of CDR approaches reduces per-unit ecological impacts compared with reliance on any single technology.⁷

3.2 SRM: Climate effects and unintended consequences

Stratospheric Aerosol Injection (SAI) and Marine Cloud Brightening (MCB) principally do not remove GHG but instead reduce the incoming solar radiation to offset warming, introducing systematic perturbations to global climate processes, while leaving ocean acidification and other CO₂-related impacts unmitigated.⁹ ¹¹

SAI: is the most extensively modeled SRM approach. Robock et al. demonstrated that both tropical and Arctic SAI injections decrease precipitation over Asian and African monsoon regions, potentially increasing food insecurity for billions.⁴⁷ A finding reinforced by Simpson et al. and Krishnamohan and Bala across multiple modelling frameworks.²⁴ ²⁵ SAI also poses significant risks to stratospheric ozone: Tilmes et al. in 2008 estimated that the sulfate aerosol injection could delay recovery of the Antarctic ozone hole by 30-70 years, a finding broadly supported by recent multi-model assessments.²⁶ ²⁷ Proctor et al. (2018) found that the sunlight reduction from SAI reduced the yield of maize and C3 crops by 9.3% and 4.8%, respectively, though more recent ARISE-SAI studies indicate that optimized multi-latitude injections can produce more favorable agricultural outcomes.²⁸ ²⁹

Marine Cloud Brightening (MCB): first proposed by Latham in 1990, uses sea salt aerosols to increase cloud albedo over ocean regions, with a potential negative radiative forcing of more than 3 W/m².³⁰ ³¹ While proposed for targeted applications such as reducing coral bleaching, Horowitz et al. found that MCB emissions increase tropospheric reactive chlorine and bromine by 20 – 40%, decreasing ozone by 3-6%, and increasing methane lifetime by 3-6%, with implications for atmospheric chemistry that extend well beyond the target regions.³²

The most severe ecological consequence of SRM is the termination shock. Jones et al. (2013) found that abrupt cessation of SAI produces rapid global warming with a mean e-folding time of approximately 6.3 years, an order of magnitude faster than gradual anthropogenic warming.³³ Trisos et al. demonstrated that the biodiversity consequences of termination shock will be severe, with temperatures velocities exceeding 10 km/yr in global biodiversity hotspots, more than double the velocities under unmitigated climate change.³⁴ Parker and Irvine (2018) argued this risk is manageable if SRM is ramped down gradually, though geopolitical disruption or natural disaster could precipitate unplanned cessation.³⁵ A 2019 study further suggested that using SRM to halve rather than fully offset warming reduces regional extremes, pointing towards moderate, complementary deployment alongside aggressive emissions cuts as potentially a more ecologically defensible approach, though the study relied on idealized solar dimming rather than realistic aerosol injection.³⁶

3.3 Long-term ecological trajectories

The ecological implications of geoengineering technologies evolve significantly over time and depend on factors such as carbon storage permanence, conventional mitigation speed, and irreversible ecological changes. CDR incurs initial ecological costs in land, water, and biodiversity, which may lessen as technologies improve and carbon is sequestered. In contrast, SRM relies on continuous deployment for climate stability, with escalating ecological consequences if halted. Table 3 offers a comparison of long-term ecological aspects for four major geoengineering approaches.

Table 3: Long-term ecological comparison of CDR and SRM approaches

Ecological Dimension

CDR: Nature-Based (BECCS, Afforestation)

CDR: Technological (DACCS, Enhanced Weathering)

SRM: Stratospheric Aerosol Injection (SAI)

SRM: Marine Cloud Brightening (MCB)

Carbon / Climate Permanence

Low–Moderate. Biotic storage is vulnerable to reversal on decadal timescales

High. Geological and geochemical storage is effectively permanent (millennia+)

None: Atmospheric CO₂ unchanged; surface warming resumes immediately upon cessation.

None: Does not remove CO₂. Cooling effects cease within days to weeks of stopping deployment.

Ecological Risks & Reversibility

Mixed. CO₂ removal reduces acidification risk progressively; large-scale BECCS risks planetary boundary violations. Afforestation albedo effects are partially reversible

Broadly Positive. Minimal ecosystem disruption; impacts are reversible if deployment ceases. Requires heavy metal monitoring for enhanced weathering.

High Risk / Low Reversibility. Acidification unabated; termination shock produces extreme biodiversity-threatening temperature velocities. Ozone depletion worsens over time

Moderate Risk. Acidification is unabated; atmospheric chemistry effects are partially reversible. Abrupt cessation causes a rapid regional climate rebound.

Ecosystem Recovery Potential

Variable: Degraded lands recover slowly under afforestation; BECCS monocultures offer limited biodiversity recovery without active restoration.

High: Low land-use footprint preserves existing ecosystems. Enhanced weathering may actively improve soil health.

Very Low post-termination: Climate velocities far exceed natural adaptation rates; recovery negligible without simultaneous CDR

Low post-cessation: Regional rebound outpaces ecosystem response in affected areas; more localized than SAI.

Lock-in, Path Dependency & Mitigation Deterrence

Moderate: BECCS-heavy pathways risk investment path dependencies and reduced urgency for structural decarbonization

Low–Moderate: Infrastructure decommissionable without ecological penalty. High current costs act as a natural brake on moral hazard.

Very High: Requires continuous maintenance once initiated; cooling effect risks substituting for rather than complementing mitigation.

Moderate: Localised deployment limits global deterrence signal, but regional cooling may reduce local decarbonization urgency.

Ecological Performance Trend Over Time

Improving: Species impact per tonne CO₂ declines with better land allocation and longer deployment

Improving significantly: Ecological footprint falls as energy systems decarbonize, and capture efficiency improves

Worsening without mitigation: Required injection rates and associated risks grow proportionally as atmospheric CO₂ rises.

Uncertain: Effects understood at small scales; long-term marine ecosystem consequences poorly characterized

The table reveals a structural asymmetry: technological CDR (DACCS, enhanced weathering) presents the most favorable long-term ecological trajectory with improving performance as energy systems decarbonize, while SAI’s ecological risk profile worsens proportionally without accompanying decarbonization The IPCC AR6 is unambiguous that no geoengineering approach can substitute for rapid and deep emissions reductions, with CDR serving as a complement within a diversified portfolio of technological and nature-based approaches, rather than a standalone solution.¹¹ ⁷

4 Social impact

4.1 Public acceptance and perception

Public awareness of geoengineering has remained remarkably low despite intensifying scientific and policy attention. Mercer et al. (2011) found that only 8% of the respondents across the US, Canada, and UK could correctly define geoengineering, while a meta-analysis of 40 quantitative studies (2015-2024) finds that emotional and ethical considerations (e.g. fear, perceived fairness, concern about “messing with nature”) are stronger predictors of acceptance than assessments of technical feasibility or economic efficiency, with trust in scientific experts and risk-framing consistently increasing conditional support.³⁷ ³⁸

CDR approaches are viewed more favorably than SRM across the literature. Pidgeon et al. (2012) first documented a public preference for CDR in the UK, and deliberative workshops in the US and UK confirm the public often prefers natural options, such as afforestation, as it is seen as addressing the root cause of climate change.³⁹ ⁴⁰ Braun et al. found German respondents ranked afforestation highest, with SAR widely rejected.⁴¹ Carlisle et al. (2020) reported that all geoengineering approaches were regarded unfavorably, but less so for CDR than SRM, as the latter was seen as an aggressive manipulator of natural systems.⁴²

The “familiarity hypothesis,” i.e., whether greater knowledge increases acceptance, yields a nuanced picture: Braun et al. and Merk et al. both found that additional information decreased acceptance for all technologies tested, including SAI.⁴¹ ⁴³ However, the Aarhus University 30-country survey shows that balanced information presentation leads average support for SRM research to exceed outright opposition, with higher support in climate-vulnerable Global South countries, though focus-group work within the same project highlights deep unease about control and demands for global governance.⁴⁴ Sovacool et al. (2024) confirmed that Global South publics and younger, lower-income respondents express greater support for climate intervention technologies.⁴⁵

Figure 1: Public support for solar radiation management across 30 countries (self-produced), data source: Aarhus University 30-country cross-national survey, Q5–Q6 and Q13⁴¹

4.2 Positive social impacts

Most literature emphasizes that geoengineering cannot substitute for emissions reductions but could reduce some of the worst social harms of unmitigated climate change if carefully governed. Positive social outcomes differ markedly across CDR and SRM: CDR generates tangible employment, public health, and food security co-benefits that accrue progressively as the deployment is scaled up, while SRM offer potential climate-moderation gains that could disproportionately benefit the world’s most vulnerable populations, but whose realization depends critically on deployment design, governance quality, and whether SRM complements rather than substitutes for mitigation. Table 2 below summarises the most empirically documented positive social impacts across all three technology categories.

Table 4: Public acceptance patterns, positive social impacts, and key caveats for SRM and CDR

Technology

Public acceptance patterns

Potential positive social impacts

Key caveats and conditions

SRM (Stratospheric Aerosol Injection and Marine Cloud Brightening)

LOW prior awareness. Support conditional on governance quality. HIGHER support in climate-vulnerable Global South countries⁴⁴⁴⁵

Rapid reduction in temperature extremes and heat mortality. Potential reduction in intercountry income inequality, with tropical countries benefiting most,.³⁶ ⁴⁶

Benefits contingent on sustained, well-governed deployment. Monsoon disruption risks negating food security gains.⁴⁷ Termination shock eliminates all benefits upon abrupt cessation 39

Natural CDR (Afforestation, reforestation, soil carbon)

Generally favourable. Seen as familiar and ethically acceptable. Preferred over engineered options in deliberative settings³⁹

Large employment potential from broader nature-based solutions.⁴⁸ Biodiversity gains. Rural income support in the Global South. Ecosystem service co-benefits.

Employment concentrated in low-wage rural roles without targeted policy support. Large-scale deployment competes with food production.¹³ Carbon storage permanence threatened by wildfire and drought 11

Engineered CDR (BECCS, DACCS, Enhanced Weathering)

MIXED. Recognised climate benefits alongside concerns about cost and corporate control. Younger and lower-income respondents show higher support⁴¹⁴⁵

Significant industrial job creation from carbon capture infrastructure.⁴⁹ Substantial air quality and public health co-benefits.⁵⁰ Agronomic yield improvements from enhanced weathering⁷²

DACCS health and employment benefits only materialize if powered by low-carbon energy,.¹⁸ Enhanced weathering yield benefits vary by soil type; heavy-metal monitoring required.²³ BECCS co-benefits contingent on avoiding food crops displacement.¹⁴

No single geoengineering approach monopolizes social benefit. Nature-based CDR dominates in employment and rural co-benefits and carries the strongest public legitimacy. Engineered CDR offers scalable health gains tied to the broader decarbonization pathway. SRM’s potential to redistribute climate burdens away from the world’s poorest is the most politically significant positive impact in literature, yet also the most conditional, disappearing entirely under poor governance, asymmetric deployment, or abrupt termination.⁴⁵

4.3 Negative social impacts

As established in Sections 2.3 and 3.1, large-scale BECCS deployment imposes severe pressures on food production and water availability, with direct social consequences especially severe for climate-vulnerable communities.¹³ ¹⁴. Enhanced weathering introduces additional health risks through heavy metal contamination and respirable silicate particulates that remain insufficiently characterized in the literature.⁵¹

SRM poses a distinct constellation of social risks. The ecological perturbations of SAI outlined in Section 3.2, namely the shifting of precipitation patterns and termination shock, translate directly into catastrophic social risks: temperatures rising at rates far exceeding natural climate change would overwhelm agricultural resilience and public health infrastructure, particularly in low-income regions that lack adaptive capacity.⁴⁷ ³⁵ Health implications of SAI also extend to ozone depletion, increasing UV-B radiation, and risks of skin cancer, cataracts, and immune suppression, with effects falling disproportionally on populations with limited healthcare access.⁵² Additionally, Kravitz et al. modeled that sufficient sulfate to offset 2% of incoming sunlight would render the sky three to five times brighter, a permanent aesthetic alteration with cultural and psychological significance.⁵³. Finally, while concerns persist that reliance on SRM may weaken mitigation efforts, research concludes that no demonstratable moral hazard with respect to SRM has been established when balanced information is provided to the public.⁵⁴.

5 Political and legal aspects

5.1 International governance and key agreements

The governance of geoengineering technologies at the international level remains fragmented and contested. Both CDR and SRM operate across national boundaries and within the global commons, necessitating multilateral coordination that existing institutions have so far been unable to deliver comprehensively.⁵⁵. The most explicit instrument for marine CDR is the 2013 amendment to the London Protocol, which prohibits marine geoengineering except for listed activities and requires a permit for ocean fertilization.⁵⁶ While a meaningful step, the amendment applies exclusively to marine environments, leaving atmospheric SRM and terrestrial CDR approaches such as DACCS and Enhanced Weathering entirely outside its scope.⁵⁶

The Convention on Biological Diversity (CBD) established a de facto moratorium on climate-related geoengineering activities that may affect biodiversity in 2010, pending an adequate scientific basis, global consensus, and justified regulatory mechanisms.⁵⁷. This moratorium was reaffirmed within the Kunming-Montreal Global Diversity Framework in 2022.⁷³ The ENMOD Convention (1978) prohibits hostile environmental modification, but its applicability to civilian geoengineering research remains legally ambiguous.⁵⁸ A landmark attempt to establish a dedicated intergovernmental expert body under UNEA failed in 2019, when Resolution 4/L.¹⁵ was withdrawn following opposition from the United States, Saudi Arabia, and Brazil, reflecting the profound political obstacles to any binding multilateral instrument.⁵⁹

Overall, the international governance landscape is characterized by a significant gap: robust binding frameworks exist for neither CDR deployment nor SRM research and deployment. The IPCC AR6 notes that the absence of adequate governance frameworks represents a major barrier to the responsible exploration of geoengineering as a supplementary climate strategy.²¹

5.2 National policy approaches

In the absence of a comprehensive international framework, the current landscape consists of a fragmented set of norms reflecting different risk tolerances, technological capabilities, and research capacities of individual states.⁶⁰. The United States has emerged as the most institutionally active jurisdiction with the 2018 and 2021 National Academies of Science (NAS) Report, recommending a $10-$25 billion investment over ten years across major CDR pathways, with an additional ~$2 billion for ocean-based approaches, as outlined by the US Department of Energy in their 2025 planning report.⁶¹ The SRM report similarly called for a dedicated research program with governance frameworks developed in parallel.⁶² At a subnational level, however, states such as Tennessee (2024), Florida (Senate Bill 56, 2025), and Montana (Senate Bill 473, 2025) have enacted outright prohibitions on weather modification, with Florida classifying unauthorized geo-engineering as a felony with penalties up to five years imprisonment and $100,000 fines.⁶³ Notably, these bans appear largely driven by political polarization, identity politic and in some cases conspiracy narratives around atmospheric intervention rather than rigorous biophysical risk assessments.

The European Union has adopted a distinctly asymmetrical approach, strongly promoting CDR while maintaining a considerably more cautious approach towards SRM technologies. The EU Carbon Removal Certification Framework (2024) establishes the world’s first comprehensive large-scale regulatory scheme for CDR activities, including BECCS, soil carbon sequestration, and enhanced weathering. ⁷³, while official EU positions on SRM emphasize the precautionary principle, reflecting the bloc’s broader risk governance philosophy.⁶⁴ The United Kingdom’s ARIA launched a multi-million-pound climate engineering research program, including small-scale outdoor SRM experiments, making the UK one of the largest global supporters of SRM research.⁶⁵ Developing nations and vulnerable states have generally adopted more restrictive stances, with Pacific Islands and African delegations at the 2024 UN Science Summit calling for non-use agreements on solar geoengineering, citing concerns that unilateral SRM deployment by major powers could alter regional precipitation patterns and monsoon systems, potentially worsening climate impacts in the Global South.⁶⁶ These dynamics illustrate a clear North-South political fault line in which the states most vulnerable to climate change are also most at risk from unilateral geoengineering interventions, while having the least capacity to monitor or respond.

5.3 Pros and cons of regulatory models

Governance literature identifies five regulatory archetypes for climate engineering: moratoriums, scientific self-regulation, national oversight, binding international treaties, and polycentric governance, each reflecting varying assumptions regarding institutional design, risk distribution, and political feasibility.⁶⁷ ⁶⁸

A moratorium approach, as embodied in CBD Decision X/33, introduced in Section 5.1, prioritizes the precautionary principle but faces a fundamental tension: it is non-binding, lacks enforcement mechanisms, and may be counterproductive for CDR given IPCC scenarios’ urgent need for gigatonne-scale removals.⁶⁹ ⁵⁷ ⁷⁰ Self-regulatory frameworks, most prominently the Oxford principles, offer flexibility without international negotiation. ⁷⁴, but the SPICE project experience demonstrates their core weakness: voluntary codes provide no enforcement mechanism and are insufficient for governing activities whose effects extend beyond the research site.⁷¹ Schoenegger and Mintz-Woo (2024) find empirical evidence that awareness of solar geoengineering research reduces individual support for emissions mitigation, suggesting that research conducted without robust governance signals may undermine the broader climate policy agenda.⁷²

National regulation offers the strongest near-term political feasibility. The EU Carbon Removal Certification Framework demonstrates how a major jurisdiction can create enforceable and detailed CDR governance without global consensus.⁷³ The critical limitation arises with SRM: transboundary effects cannot be adequately governed nationally, and the termination risks documented in Section 3.2 could produce climate change at a rate far exceeding the original problem.³³ ³⁵ A binding international treaty modeled on the Montreal Protocol could address this, offering institutional capacity for research permitting, impact assessment, liability, and deployment authorization.⁷⁴ However, the 2019 UNEA governance failure detailed in Section 5.1 illustrates the depth of political obstacles to any such instrument.⁵⁹ Polycentric governance, which comprises the layering of overlapping regulatory authorities at local, national, regional, and international levels, has emerged as the most widely advocated framework. Morrison et al. (2017) demonstrated that polycentric systems are more resilient than single-institution frameworks⁶⁸, and the IRGC recommends this architecture as the most realistic path toward effective geoengineering governance, while acknowledging that coordination complexity and inconsistent standards across jurisdictions remain significant disadvantages.⁶⁰

A recurring theme is the need to treat CDR and SRM asymmetrically. CDR approaches with verifiable local effects, such as afforestation, DACCS, or enhanced weathering, are more amenable to national certification and MRV frameworks, as demonstrated by the EU’s instrument.⁷³ SRM requires fundamentally stricter multilateral oversight owing to its potential for rapid, geographically uneven effects, abrupt termination risks, and an absence of natural analogues informing risk assessment.⁶² The prevailing scholarly consensus is that differentiated, polycentric governance building on existing multilateral instruments provides the most viable pathway, provided that meaningful participation by the most climate-vulnerable states is structurally guaranteed.¹¹ ⁶⁰

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26
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28
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29
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31
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32
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