The Carnegie Climate Governance Initiative has the best summary of SAI I've read.
1. Science of aerosols in the stratosphere
Mt. Pinatubo, Philippines (1991)
El Chichón, Mexico (1982)
Mt. Agung, Indonesia (1963)
Large volcanic eruptions have been directly responsible for significant temperature drops for 2-3 years following the explosion.
Calcite aerosols may work better than sulfates:
2. Operational Feasibility
Aurora 2010 report - with David Keith
McClellan 2012 - one of the most cited
Detailed cost breakdown & operational plan.
"We also conclude that developing a new, purpose-built high-altitude tanker with substantial payload capabilities would neither be technologically difficult nor prohibitively expensive. We calculate early-year costs of ∼$1500 ton−1 of material deployed, resulting in average costs of ∼$2.25 billion yr−1 over the first 15 years of deployment. We further calculate the number of flights at ∼4000 in year one, linearly increasing by ∼4000 yr−1. We conclude by arguing that, while cheap, such an aircraft-based program would unlikely be a secret, given the need for thousands of flights annually by airliner-sized aircraft operating from an international array of bases."
Alumina or diamond particles may work better than sulfates, with less ozone loss and stratospheric heating.
Liability for damages:
3. Risks, effectiveness, and governance
McCusker, The climate response to stratospheric sulfate injections and implications for addressing climate emergencies (2012)
"We find that when global average warming is roughly canceled by aerosols, temperature changes in the polar regions are still 20-50% of the changes in a warmed world."
- So: will work for equatorial regions, but polar temperature change is
National Academies of Sciences, Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance (2021)
300-page report, written by a giant committee of US scientists, that proposes an enormous number of highly bureaucratic processes for future research (which the report views as a necessary pre-requisite for any kind of deployment) and advises that U.S. Global Change Research Program (USGCRP) should be in charge of the effort.
RAND, Climate Control, 2021
Current international treaties including Environmental Modification Treaty (ENMOD), UNFCCC, Montreal Protocol (Ozone), Convention on Biological Diversity (CBD), and London Convention and London Protocol (LC/LP) are irrelevant and/or do not have an enforcement mechanism.
4. Public & Elite Perception
The politics of geoengineering are just beginning to reveal themselves. Based on a few data points, it appears that:
- the far left is (or will be) opposed to geoengineering
- the scientific community is cautious and would require more research before action
- no one today is advocating for geoengineering
There would need to be a pretty radical shift in the Overton window to create a possibility for geoengineering action.
Backlash article in The Hill, April 4, 2021 - arguing (a) moral hazard & (b) social justice (?)