Stratospheric Aerosol Injection (SAI) – A Controversial Climate Intervention Technology

Context:

A new study published in Earth’s Future explores a more practical approach to Stratospheric Aerosol Injection (SAI), a geoengineering technique aimed at cooling the planet by injecting reflective aerosols into the stratosphere.

What is SAI?

• Stratospheric Aerosol Injection involves releasing particles (e.g., sulphur dioxide) at ~20 km altitude to reflect sunlight and reduce global temperatures.

• Inspired by volcanic eruptions (e.g., Mount Pinatubo, 1991) which had a temporary cooling effect on Earth.

• Controversial due to global-scale impacts, ethical concerns, and unpredictable side effects.

New Findings from the Study:

• Researchers used the UKESM1 climate model to simulate different SAI strategies:

  • Injecting 12 million tonnes/year of sulphur dioxide at 13 km could cool the planet by 0.6°C.

  • For 1°C cooling, 21 million tonnes/year needed.

  • Injecting at higher altitudes in subtropics could achieve same effect with just 7.6 million tonnes/year.

• Lower-altitude injection in polar and extratropical regions is technically more feasible using existing aircraft, though less efficient.

• Modified aircraft like Boeing 777F would be required for safe aerosol transport.

Advantages:

• Cost-effective and quicker to deploy than high-altitude approaches.

• Does not require specially designed aircraft, which would take a decade and billions to develop.

• Can begin sooner with modifications to current fleet.

Risks & Concerns:

• Greater aerosol use increases the risk of:

  • Ozone layer damage

  • Acid rain

  • Uneven global cooling (more effect in poles than tropics)

  • Complacency in emission reduction efforts

• Social and geopolitical challenges: effects are global and unilateral action can harm other nations.

• Critics argue the technology is “ungovernable” in a fair and democratic way.

Global Position:

• 2021: US National Academies recommended research into solar geoengineering.

• 2022: International scholars demanded a moratorium, citing governance and fairness concerns.

UPSC Relevance:

GS Paper III – Environment and Technology

• Climate engineering, mitigation vs adaptation

• Technological interventions and ethical dimensions

• International climate diplomacy and governance challenges