THE CONTEXT: Global greenhouse-gas (GHG) emissions hit a new record in 2024; current Nationally Determined Contributions (NDCs) put the planet on a 2.5-2.9 °C pathway. The gap between what science demands and what politics delivers has led some researchers to revisit solar geo-engineering, especially SAI, as a risk-containment rather than a risk-aversion strategy.
BACKGROUND
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- Volcanic clue: The 1991 Mount Pinatubo eruption lofted ~17 Mt of sulphur dioxide (SO₂) into the stratosphere and cooled the globe by ~0.5 °C for two years.
- From theory to labs: Post-2006 modelling (Harvard, Oxford, IITM) matured concepts; the 2021 U.S. National Academies report called for a $200 million, decade-long, transparent research programme.
- Policy hesitation: The Convention on Biological Diversity (CBD) placed a de facto moratorium on large-scale SRM in 2010, invoking the precautionary principle
WHAT–WHY–HOW” THEORETICAL FRAMEWORK
| ASPECT | DETAILS |
|---|---|
| WHAT | SAI is the deliberate dispersion of light-scattering particles (classically SO₂; experimental solids include calcium carbonate, diamond, and even lunar dust) into the lower stratosphere to increase albedo and reduce net radiative forcing. |
| WHY | It offers a fast-acting thermostat: surface temperatures respond within months, potentially limiting overshoot and buying time for deep-decarbonization and negative-emission technologies. |
| HOW | Particles oxidise to sulphuric-acid aerosols, forming a ~0.1–1 µm veil. Residence time, optical depth, and meridional circulation determine efficacy; hence, altitude, latitude, and injection season are critical control knobs. |
TECHNICAL DETAILS & RECENT RESEARCH
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- Low-altitude polar option: UCL (Duffey et al., 2025) modelled injections at 13 km over 60° N/S during local spring–summer. 12 Mt SO₂ yr⁻¹ can yield ~0.6 °C global cooling; 21 Mt produces ~1 °C.
- Aircraft retro-fit: 102 modified Boeing 777F freighters with insulated double-walled, pressurised tanks could deliver the 21 Mt payload in under five years of scale-up, avoiding the decade-long wait for purpose-built high-altitude platforms.
- Costing: Harvard Wake Smith’s 2024 assessment pegs a 1 °C programme at ~USD 15 billion yr⁻¹ (capex + opex), roughly 0.015 % of global GDP.
CURRENT SCENARIO & SIGNIFICANCE
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- UNEP and WMO convened the first joint science-policy dialogue on SRM governance in May 2025 (Geneva).
- A draft resolution at UNEA-6 proposes an expert group to evaluate SRM risks before UNEA-7.
- Financially, SAI is orders of magnitude cheaper than net-zero transformation but cannot replace emission cuts – it merely masks radiative imbalance.
DRIVERS ACCELERATING THE DEBATE:
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- Emissions Gap – the 2024 UNEP report warns the 1.5 °C guard-rail may be crossed before 2030.
- Cryospheric Tipping Points – Antarctic and Greenland ice-loss studies show SAI could halve ice-sheet mass loss if begun by 2040.
- Extreme-event Anxiety – unprecedented heatwaves (Delhi 2024, Phoenix 2024) spur ‘climate-emergency’ narratives, pressuring policymakers.
INDIAN CONTEXT:
| DIMENSION | EVIDENCE |
|---|---|
| RESEARCH | MoES–PMOD/WRC MoU (Sept 2024) on solid-particle geoengineering; IITM participates in GeoMIP-G6sulfur experiments assessing monsoon sensitivity. |
| VULNERABILITY | A 1 °C rise cuts wheat yields by ~5 %; IMD attributes 2024 heat deaths >2 800 to compounded warming. |
| POLICY GAP | No dedicated SAI policy; NAPCC focuses on mitigation/adaptation. Geo-engineering appears in ‘Mission Mausam’ science agenda but lacks a regulatory anchor. |
GLOBAL GOVERNANCE LANDSCAPE
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- Normative vacuum: CBD moratorium (2010) is non-binding; the Vienna Convention ozone regime studies SRM but lacks enforcement.
- Civil-society pushback: 2023 call by 60+ scholars for a moratorium on outdoor SRM experiments.
- Ethics & equity: Carnegie Climate Governance Initiative (C2G) stresses free, prior and informed consent of vulnerable states.
THE ISSUES:
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- Physical uncertainties: Heterogeneous chemistry may delay ozone-hole recovery; stratospheric heating can alter Brewer–Dobson circulation.
- Regional climate distortion: Models project weakened South-Asian summer monsoon, jeopardising Indian agriculture.
- Termination shock: Sudden stop would unleash up to 0.4 °C yr⁻¹ rebound, overwhelming adaptation capacity.
- Moral hazard & mitigation deterrence: Perceived ‘quick fix’ could slow energy transition investments.
- Governance asymmetry: A single mid-income state could launch SAI unilaterally; affected neighbours currently lack legal recourse.
- Monitoring & liability: No agreed baseline for attributing extreme events to SAI; compensation mechanisms absent.
- Ecosystem acidification: Downwind acid deposition risks to boreal forests and Arctic permafrost remain understudied.
- Technological lock-in: Once infrastructure is built, it creates vested interests and path dependence.
THE WAY FORWARD:
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- Forge a multilateral ‘Geneva Protocol on Solar Radiation Modification’: It should mandate prior informed consent, environmental impact assessment, and liability insurance. Embedding it under the UN Environment Assembly will lend universal legitimacy.
- Create a Global SAI Risk Observatory: Satellite, lidar, and balloon networks must track aerosol optical depth and chemistry in near-real-time. India can host a Southern-Asia node leveraging ISRO’s Megha-Tropiques-2 platform.
- Adopt a ‘Mitigation First, Intervention Last’ hierarchy in national climate policies: Legislate a carbon-budget corridor aligned with net-zero by 2070 before contemplating any deployment. This preserves moral clarity and coherence with the Paris Agreement.
- Invest in regional impact modelling and public-interest science: IITM and NCAP should quantify monsoon, agriculture and health outcomes under diverse SAI scenarios. Transparent, open-source models counter misinformation.
- Build national competency on stratospheric chemistry and aviation retrofit standards: DGCA, in partnership with HAL, could frame airworthiness norms for aerosol-dispensing pods. Early engagement avoids unsafe, private experiments.
- Establish a Climate Technology Ethics Commission: Including philosophers, civil society, and indigenous representatives, it should vet outdoor trials. Embedding social licence reduces public backlash.
- Leverage carbon pricing to fund negative-emission pathways: Redirect a share of carbon-market revenue to afforestation and Bioenergy with Carbon Capture and Storage (BECCS), making SAI a bridge not a destination.
- Negotiate equitable compensation and adaptation funds: Countries benefiting disproportionately must contribute to a ‘Stratospheric Solidarity Fund’. This aligns SAI with the UNFCCC principle of Common but Differentiated Responsibilities.
THE CONCLUSION:
Stratospheric Aerosol Injection is neither a silver bullet nor scientific heresy; it is a risk-weighted hedge against worst-case warming. India, which champions climate justice, cannot ignore SAI research; yet, it must anchor any exploration in precaution, transparency, and relentless emission cuts. Therefore, mitigate first, govern better, intervene last.
UPSC PAST YEAR QUESTION:
Q. Troposphere is a very significant atmospheric layer that determines weather processes. How? 2022
MAINS PRACTICE QUESTION:
Q. Stratospheric Aerosol Injection (SAI) is increasingly discussed as a climate-risk management tool. Examine its scientific feasibility, potential impacts on India’s monsoon-dependent economy, and the challenges of governing such a technology at the global level.
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