Stratospheric Aerosol Injection (SAI) as a Climate Intervention Technique
The global dependency on fossil fuels remains a critical issue, with greenhouse gas emissions on the rise. In efforts to combat climate change, some researchers propose technologies like Stratospheric Aerosol Injection (SAI) to directly cool the planet.
Overview of SAI
- SAI involves injecting aerosols into the stratosphere to reduce sunlight reaching the Earth's surface.
- This method is inspired by volcanic eruptions, which naturally cool the planet by releasing aerosols.
- The effectiveness of SAI depends on the type of material, timing, and location of injection.
Technical Challenges and Approaches
- SAI is typically considered at altitudes above 20 km, requiring specially designed aircraft.
- A study explored using existing aircraft for SAI at lower altitudes, especially in polar regions where the stratosphere is more accessible.
- High-altitude injections are more effective as particles remain longer in the stratosphere.
- Low-altitude injections are less technically challenging and could be more cost-effective.
Simulation and Findings
- Researchers simulated various injection strategies using the UK Earth System Model 1 (UKESM1).
- Injecting 12 million tonnes of sulphur dioxide annually at 13 km during spring and summer could achieve a cooling effect of 0.6º C.
- Achieving a 1º C cooling effect would require injecting 21 million tonnes annually.
- Injecting at higher altitudes in the subtropics could reduce the required amount to 7.6 million tonnes per year.
Risks and Controversies
- SAI poses risks such as delayed ozone recovery, acid rain, and geopolitical tensions.
- The cooling effect may lead to complacency in emissions reduction efforts.
- SAI's global impact is a point of contention, as all countries could be affected differently.
- International calls have been made for a moratorium on solar geoengineering research due to governance challenges.
The study acknowledges limitations and calls for further research, highlighting the complexity and potential unintended consequences of SAI.