Climate change, geoengineering, and existential risk

by Halstead 20th Mar 201811 comments


A paper I have written on a form of geoengineering known as 'stratospheric aerosol injection' has recently been published in Futures. The paper explores whether, assuming that reducing existential risk is overwhelmingly important, stratospheric aerosol injection should be researched. The following aspects are likely to be of some interests to EAs:

  • It provides, to my knowledge, the most comprehensive existing discussion of the scale of the existential risk posed by climate change. 
  • It provides the most comprehensive and up to date discussion of geoengineering from an existential risk reduction point of view. 
  • The framework it uses to discuss the problem of 'moral hazard' may be of use in other domains (though the framework is David Morrow's, not my own).

The paper is available on my website, and on my academia page. All views are my own, not my employer's. All comments are welcome. 



Abstract: In the wake of the continued failure to mitigate greenhouse gases, researchers have explored the possibility of injecting aerosols into the stratosphere in order to cool global temperatures. This paper discusses whether Stratospheric Aerosol Injection (SAI) should be researched, on the controversial ethical assumption that reducing existential risk is overwhelmingly morally important. On the one hand, SAI could eliminate the environmental existential risks of climate change (arguably around a 1% chance of catastrophe), and reduce the risks of interstate conflict associated with extreme warming. Moreover, the risks of termination shock and unilateral deployment are overstated. On the other hand, SAI introduces risks of interstate conflict which are very difficult to quantify. Research into these security risks would be valuable, but also risks reducing willingness to mitigate. I conclude that the decision about whether to research SAI is one of ‘deep uncertainty’ or ‘complex cluelessness’, but that there is a tentative case for research initially primarily focused on the governance and security aspects of SAI.


  • It is uncertain whether Stratospheric Aerosol Injection(SAI) research is justifiable, but a tentative case be made for security-focused research.
  • SAI would eliminate the arguable environmental existential risks of climate change (<1% – 3.5%).
  • It is extremely unclear whether SAI would reduce willingness to mitigate, and extensive efforts should be made to reduce the risk of mitigation obstruction.
  • Termination shock risk is overstated.
  • The risk of unilateral deployment is overstated, but SAI introduces other serious security risks.