Works in Progress Podcast Sunscreen for the planet: Geoengineering a cooler planet
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Mar 20, 2026 They explore deliberately cooling the planet by reflecting sunlight using aerosols, inspired by volcanic eruptions. The discussion covers how aerosols change Earth’s energy balance and how much sulfur might be needed. Listeners hear proposals for phased field tests, monitoring needs, governance challenges, and the logistics and costs of potential deployment.
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Volcanoes Proved Stratospheric Cooling Works
- Volcanic sulphur dioxide can cool the planet by forming reflective stratospheric aerosols.
- Mount Pinatubo's 17 million tonnes cut global temperatures ~0.5°C for about 18 months, validating aerosol sunlight‑reflection physics.
Stratosphere Lifetimes Make Sulfur Efficient
- Stratospheric aerosols are far more effective per tonne than tropospheric ones because they persist longer and spread globally.
- Aerosols in the stratosphere last 12–18 months and Pinatubo reduced incoming energy ~2.5 W/m² causing ~0.5°C cooling.
A Quarter Of Current Sulfur Could Offset Warming
- Redirecting a fraction of current sulfur emissions to the stratosphere could offset historical and projected warming.
- If 20 million tonnes of today's 80 million tonnes reached the stratosphere it could balance past and expected future warming.