New Paper on US, China, and Big Geoengineering
Josh Horton
Stratospheric aerosol injection, which would reflect a small fraction of sunlight away from the Earth to lower temperatures, involves many unanswered questions. One of these is, who could deploy it? We consider this with reference to a scenario in which global temperatures are reduced by 1°C by midcentury; we term this a ‘PLUS’ deployment—Planetary, Large- scale, Uninterrupted, and Speedy. The technical requirements of a PLUS deployment—a fleet of a hundred or more specialized air- craft—limit the number of capable actors to ten states. The geopolitical requirements broad- spectrum capabilities sufficient to overcome external constraints—mean that only the US and China are capable of implementing unilaterally against strong opposition. As such, the US and China will be decisive in determining whether and how a PLUS- type deployment takes place. In particular, the degree of Sino- American alignment on this issue will strongly influence the likelihood of a PLUS deployment and its disruptive potential. We examine three cases in which activities with the potential to harm global commons were debated during the Cold War: scientific research in Antarctica, atmospheric testing of nuclear weapons, and experiments in outer space. Backed by evidence from these cases, we then consider several implications of our findings.
Josh Horton
Douglas MacMartin
Hi Josh,
This is great; so glad to see this out finally!
One question, one comment:
- Curious why you included countries on the list of having the technical capability that don’t make aircraft engines; of the two (engines or airframe) would seem to me that the engines are both harder to develop capacity from scratch, and harder to acquire from another country if that country doesn’t want you to buy them. I wouldn’t have included Canada or India or Brazil on the list for this reason.
- The scenario you describe is entirely reasonable choice for this paper, but I’m curious about the phrase “it would involve a cooling rate of approximately 0.5°C per decade, more than twice as fast as current warming rates and enough to create obvious risks”. Current rate of warming is close to +0.25C per decade, so increasing the amount of cooling by 0.5C per decade simply leaves the overall rate of change the same as it is now but with the opposite sign. (So that a decade into deployment, the global mean temperature would be roughly what it had been a decade before deployment started.) Given that most ecosystems (or human systems) won’t yet have adapted to temperatures at the start of deployment, I’d think it actually quite safe to assume that provided that an incremental use of SAI does indeed reduce risks in general, while it’s clear that there is some threshold that is too much, or too fast, that using enough to bring temperatures back towards something ecosystems (and people) are better adapted to would still reduce risks and be quite clearly below that unknown threshold. Yet you write that this would create “obvious risks”… given that it isn’t obvious to me, it obviously isn’t obvious, so I’m curious what risks you were referring to.
doug
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Joshua Horton
Doug — Addressing the first item below, there was an earlier draft of the paper that dwelt on just the distinction you note regarding engine vs airframe capabilities. I agree that engines are harder and and the capabilities are rarer, but as matters shook out, we ended up cutting this text and blurring the distinction.
Wake SmithLecturer: Yale School of the Environment &Research Fellow: Mossavar-Rahmani Center for Business & Government; Harvard Kennedy School
From: Douglas MacMartin <dgm...@cornell.edu>
Sent: Wednesday, April 30, 2025 9:57 AM
To: joshuah...@gmail.com <joshuah...@gmail.com>; geoengineering <geoengi...@googlegroups.com>
Cc: Smith, Wake <wake....@yale.edu>
Subject: RE: [geo] New Paper on US, China, and Big Geoengineering
Hi Josh,
This is great; so glad to see this out finally!
One question, one comment:
- Curious why you included countries on the list of having the technical capability that don’t make aircraft engines; of the two (engines or airframe) would seem to me that the engines are both harder to develop capacity from scratch, and harder to acquire from another country if that country doesn’t want you to buy them. I wouldn’t have included Canada or India or Brazil on the list for this reason.
- The scenario you describe is entirely reasonable choice for this paper, but I’m curious about the phrase “it would involve a cooling rate of approximately 0.5°C per decade, more than twice as fast as current warming rates and enough to create obvious risks”. Current rate of warming is close to +0.25C per decade, so increasing the amount of cooling by 0.5C per decade simply leaves the overall rate of change the same as it is now but with the opposite sign. (So that a decade into deployment, the global mean temperature would be roughly what it had been a decade before deployment started.) Given that most ecosystems (or human systems) won’t yet have adapted to temperatures at the start of deployment, I’d think it actually quite safe to assume that provided that an incremental use of SAI does indeed reduce risks in general, while it’s clear that there is some threshold that is too much, or too fast, that using enough to bring temperatures back towards something ecosystems (and people) are better adapted to would still reduce risks and be quite clearly below that unknown threshold. Yet you write that this would create “obvious risks”… given that it isn’t obvious to me, it obviously isn’t obvious, so I’m curious what risks you were referring to.
doug
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