Stratospheric Aerosol Injection (SAI): New Study Finds Cost-Effective Geoengineering Approach to Cool Earth

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June 09, 2025

Stratospheric Aerosol Injection (SAI): New Study Finds Cost-Effective Geoengineering Approach to Cool Earth

A new study published in ‘Earth’s Future’ explores a cost-effective approach to Stratospheric Aerosol Injection (SAI), a form of solar geoengineering aimed at cooling the Earth.

About Stratospheric Aerosol Injection (SAI)

  • SAI is a geoengineering technique that involves injecting reflective particles (like sulphur dioxide) into the stratosphere to reflect sunlight and cool the planet.
    • It mimics the natural cooling effect observed after major volcanic eruptions like Mount Pinatubo in 1991.
    • Currently, it is intended as a climate intervention strategy to temporarily reduce global warming.

Key Findings of the Recent Study Regarding SAI

  • Low-Altitude Injection: Injecting aerosols at 13 km using modified existing aircraft is technically possible and less costly than high-altitude methods.
  • Cooling Potential Quantified: Spraying 12 million tonnes of sulphur dioxide annually at 13 km can cool the Earth by around 0.6°C.
  • Cooling and Aerosol: To achieve 1°C cooling at lower altitudes, 21 million tonnes/year is needed, nearly three times the amount required at higher altitudes. Thereby, greater cooling requires greater aerosol.
  • High-Altitude Injection: Injecting at higher subtropical altitudes needs only 7.6 million tonnes/year for the same cooling effect and is more effective, due to longer particle residence time.
  • Polar Regions: Cooling effect is stronger in polar regions, while tropical areas,where warming is worse, have seen less benefit.
  • Faster Deployment Possible: Using existing aircraft enables earlier deployment compared to waiting for custom high-altitude aircraft, which could take a decade to build.

Global Views on SAI Governance

  • 2021: US National Academies advised funding SAI research with transparency.
  • 2022: Global scholar coalition called for moratorium, citing SAI as “ungovernable” and democratically unmanageable.
  • Intergovernmental Panel on Climate Change (IPCC) cautions against reliance on SAI and promotes mitigation and adaptation instead.

Risks Related To the Deployment of SAI

  • Environmental Risks:
    • Acid Rain: Increased sulphur use may lead to acidification of ecosystems.
    • Ozone Layer Damage: Deployment of SAI could delay recovery of the ozone layer by enhancing chemical reactions that destroy ozone.
    • Uneven Climate Effects: Cooling is more pronounced in polar regions, leaving tropical zones more vulnerable.
  • Social and Geopolitical Concerns:
    • Unilateral Action: No global regulatory framework currently exists. If a single country deploys SAI, it can alter global climate patterns, raising ethical and sovereignty issues.
    • Conflict Risk: SAI may trigger international disputes and strain global climate governance frameworks.

Conclusion

Further studies with wider simulations are essential to assess long-term impacts. However, SAI must not replace emission cuts and  global rules are needed to avoid misuse and conflicts

Aerosols

  • Aerosols are suspensions of tiny solid particles or liquid droplets in a gas, usually in the air.
  • They can be natural or anthropogenic (human-generated).
  • They significantly influence climate, weather, air quality, and even human health.

Types of Aerosols

1. Primary Aerosols:

  • Directly emitted into the atmosphere.
  • Examples: Sea spray, Mineral dust, Volcanic ash and Smoke from combustion, etc.

2. Secondary Aerosols:

  • Formed within the atmosphere via chemical reactions involving precursor gases.
  • Examples:
    • Sulfate aerosols from volcanic or industrial SO₂
    • Nitrate aerosols from NOx emissions

3. Biological Aerosols (Bioaerosols):

  • Composed of airborne biological particles.
  • Examples: Viruses, Bacteria, Fungal spores and Pollen, etc.

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UDAAN PRELIMS WALLAH
Comprehensive coverage with a concise format
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