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.

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. 

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