In News:

A study recently published in the journal Earth’s Future offered an innovative approach to SAI technique that could reduce its costs but also bring it closer to fruition despite the opposition to it.

What is Stratospheric Aerosol Injection (SAI)?

• SAI is a proposed solar geoengineering technique to cool the Earth by injecting reflective aerosols (e.g. sulphur dioxide) into the stratosphere to reflect sunlight and reduce surface temperatures.
• Inspired by volcanic eruptions, like Mount Pinatubo (1991), which naturally cooled the Earth by emitting aerosols.

Recent Study Highlights (June 2025)

• Published in Earth’s Future journal.
• Led by Alistair Duffey, University College London.
• Used UK Earth System Model 1 (UKESM1) for climate simulations.

Key Findings

• Injecting 12 million tonnes of sulphur dioxide annually at 13 km altitude (spring/summer in each hemisphere) could cool the Earth by ~0.6°C.
• To cool by 1°C, ~21 million tonnes/year are needed at that altitude.
• Only 7.6 million tonnes/year are needed at higher altitudes (subtropics) for the same cooling.

Innovative Proposal

• Low-altitude SAI using modified existing aircraft (e.g. Boeing 777F) instead of specially designed high-altitude aircraft:
  • Stratosphere is lower near poles (12–13 km), so current aircraft can reach it.
  • Cost-effective and faster to deploy than high-altitude (~20 km) methods.
  • Could begin within years, rather than a decade-long wait for new aircraft.

Risks and Concerns

• Tripling aerosol quantity (in low-altitude strategy) raises:
  • Ozone depletion
  • Acid rain
  • Altered weather patterns
  • Uneven global effects (benefits poles more, tropics less)
  • Moral hazard: may reduce incentives to cut emissions.
• Governance challenge: One country’s action impacts all nations → risk of geopolitical conflict.

Why it matters

• Global GHG emissions are still rising.
• Climate mitigation through decarbonisation is slow and politically vulnerable.
• Technologies like SAI offer a stopgap, but not a substitute for emission cuts.