A Case for Climate Engineering is a little book that makes a high-level pitch for careful geoengineering. It is designed to convince policy makers in a hurry and doesn't go into deep detail, but offers a good overview of the methods, drawbacks, and challenges.
Author @DKeithClimate is a good Twitter follow, btw.
- The most likely approach is stratospheric aerosol injection — spraying reflective droplets into the stratosphere, at 20km.
- These droplets would raise the albedo of the planet — reflect a larger percentage of sunlight back into space, cooling the planet.
- The current cheapest candidate would be a fine sulfuric acid mist.
- Stratospheric aerosol injection is feasible. Developing a program would likely cost 5 years and 1bn USD.
- It could be accomplished using Gulfstream jets retrofitted with low-bypass jet engines and dispersal hardware.
- Sulfurs have the side-effect of depleting the Ozone Layer. There's a balance to be struck.
- The technical challenge is not the equipment for spraying, but the tools for monitoring and observing effectiveness and side-effects.
- Geoengineering is not a binary yes/no. In particular, each application of stratospheric aerosol injection would have an effect over several years, constantly needing to be re-upped. This has the beneficial side-effect of making it possible to "play with the thermostat" without committing.
- A slow-ramp scenario would buy us time to transition to renewables, develop tech, and generally find some new to cling to.
- This approach could be used to cut average global warming in half for half a century.
- The total amount of sulfer disbursed would have to be increased year-over-year to keep up with additional CO2 emitted during the course of the year.
- Only 2 aircraft would be needed to start.
- In 10 years, you would likely need 10 aircraft to keep up with additional CO2 emissions in the intervening years.
- By 2070, you would need to inject 1m tons per year, with about 100 aircraft.
- Within this timeframe, we could likely engineer an alternative to sulfates. Several proposals exist.
- Warming and cooling are not homogenous across the planet. Warming will be stronger in polar regions than near the equator. Monitoring would have to be done to strategically apply aerosols for best results.
- Geoengineering does not stop ocean acidification
- Sulfurs have the side-effect of depleting the Ozone Layer. However, it is likely other materials could be developed without this side-effect in the relevant timeframe (~50 years).
- We can estimate the negative effects of disbursing 1m / y tons of sulfur by looking at the eruption of Mt Pinatubo (8m tons of sulfer) or the 50m tons of sulfur we pump into the air as pollution.
- If you stop disbursing, the sulfers will disappear from the stratosphere in a few years, so the risks are comparatively small.