Solar geoengineering technologies (also known as solar radiation management) are receiving increasing attention as one option for addressing climate change, with their potential to partially offset the global warming caused by the increased emissions of greenhouse gases.

However, different countries may have different preferences over the optimal amount of cooling. Additionally, if the cost of these technologies is low it is possible that the country with the strongest incentive for cooling (the so-called ‘free-driver’) can afford to impose its preference on other countries – and with it, possible negative effects.

This research investigates the potential impacts of counter-geoengineering technologies, which could negate the cooling effects of solar geoengineering. Countries could use counter-geoengineering to counteract what they regard as harmful solar geoengineering instigated by another. The researchers ask whether the presence of counter-geoengineering could tip the balance away from the free-driver problem in favour of international cooperation. They find that the presence of counter-geoengineering would make the risk of unilateral action to cool the climate less likely, but not always with benign effects.

Key points for decision-makers

  • Solar geoengineering would work by releasing cooling particles (sulphate aerosols) into the stratosphere or by making marine clouds more reflective of sunlight.
  • Counter-geoengineering could be either ‘neutralising’ (e.g. injecting a base to counteract the effect of sulphate aerosols) or ‘countervailing’ (e.g. releasing a warming agent to reverse the effects of aerosols).
  • This research uses game theory to analyse countries’ strategic interaction surrounding solar geoengineering and counter-geoengineering.
  • The study finds a number of possible outcomes from the presence of counter-geoengineering technologies. The outcome largely depends on how much disagreement there is over countries’ preferred global temperature.
  • It finds that when climate intervention is restricted to cooling, the typical outcome is that the country suffering the most from climate change (the ‘free-driver’) may set global temperatures as it pleases, possibly causing damage to other countries.
  • The game shows that the availability of counter-geoengineering could lead to a harmful ‘climate clash’: countries would engage in a non-cooperative escalation of opposing climate interventions, wasting significant resources in offsetting the impacts of solar geoengineering and counter-geoengineering deployments.
  • This destructive prospect is the reason why the existence of counter-geoengineering can significantly increase countries’ willingness to cooperate over the deployment of solar geoengineering, enhancing collective welfare; the would-be unilateral actor understands that the threat of a ‘climate clash’ would harm the country substantially and wishes to avoid this.
  • However, other countries may prefer cooperation in the form of a moratorium on the use of both types of climatic intervention, potentially reducing global welfare as any benefits of solar geoengineering would be lost.
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