Stratospheric Aerosol Injection

Why in news: SAI involves injecting aerosols into the stratosphere to reflect sunlight and cool the planet. Inspired by volcanic eruptions, which naturally cool Earth by spewing aerosols into the atmosphere. Suggested as a supplement to emissions reductions, not a replacement.

• Traditional SAI focuses on high-altitude injections (20 km+), requiring specially designed aircraft. New approach proposes lower-altitude injections (13 km) in polar and extratropical regions.
• 12 mn tonnes/yr of sulphur dioxide, sulphur aerosols, titanium dioxide or calcium carbonate at 13km could cool planet by 0.6°C. Lower altitude injections are cheaper and quicker.

Challenges

• Lower altitude injections risk aerosols being washed out by rain, reducing long-term effectiveness.
• May cause ozone depletion, acid rain, and delayed ozone hole recovery.
• Cooling effect is stronger at the poles but less effective where warming is most severe (tropics).
• Sea Curtains/ Walls: Blocking warm ocean water from reaching ice using buoyant structures attached to seabed.
• Sea Ice Management: Scattering glass microbeads to increase ice reflectivity and thickness.
• Basal Water Removal: Removing subglacial water under glaciers to slow ice movement and sea-level rise.
• Ocean Fertilisation: Adding nutrients like iron to oceans to stimulate phytoplankton growth and absorb more CO₂.

Concerns with Stratospheric Aerosol Injection (SAI)

• Research focuses on sulphur dioxide, sulphur aerosols, titanium dioxide, and calcium carbonate.
• Ineffective in polar winters (no sunlight to reflect) and redundant in summers due to existing natural reflectivity.
• Risk of termination shocks — sudden temperature spikes if stopped.
• Could disrupt global weather patterns, affecting food and national security.

Concerns with Sea Curtains and Sea Walls

• High logistical costs in remote regions like the Amundsen Sea.
• May cause negative impacts on ocean circulation and marine life.

Concerns with Sea Ice Management

• Ecotoxicity concerns and possible harm to zooplankton.
• Requires 360 million tonnes of glass microbeads annually — equal to global plastic production.

Concerns with Basal Water Removal and Ocean Fertilisation

• Basal Water Removal is emissions-intensive, needs constant monitoring, and offers limited impact.
• Ocean Fertilisation causes uncontrolled phytoplankton growth, disrupting food chains and nutrient cycles.