Shorten the solar-geoengineering timeline?

In his article on climate tipping points, Michael Edgeworth McIntyre highlights how the various synergies among contributing factors mean there are multiple possible pathways toward unpredictable adverse climate impacts (Physics Today, March 2023, page 44 ). Only a subset of those pathways need to be self-reinforcing in an adverse way to produce more severe or more abrupt harmful outcomes than models predict.

In that context, it can be useful to reconsider the role of solar-radiation management (SRM), also known as solar geoengineering—a strategy that involves reflecting some of the Sun’s energy back into space as a means of combating climate change. Proposed SRM strategies include the injection of aerosols into the atmosphere, the brightening of marine clouds via sea-salt injection, and even the creation of floating mirrors in space.

The well-known potential drawbacks of those strategies should be viewed in the context of growing indications that climate degradation will outpace decarbonization. McIntyre’s survey of climate contingencies serves as a reminder that the decision of whether to implement SRM is a choice between the lesser of two problematic scenarios.

In that regard, two points are pertinent. First, the choice is not binary. A limited deployment of SRM that fractionally slows the global-temperature increase over several decades might yield benefits that greatly outweigh the associated risks. Second, the possible rapid onset of extreme climate scenarios could accentuate the need for timely SRM deployment, which raises the question of how quickly that need could be met. The present approach, which holds more-concrete steps in abeyance pending the outcome of ongoing studies of SRM effectiveness and drawbacks and the clarification of governance, could mean that we wouldn’t see any tangible mitigation benefits for decades. Aerosol dispersal, for one, will eventually require the design and construction of aircraft, among other large-scale industrial tasks.

The adverse impacts of that lag could be enormous. Parallel efforts, analogous to the COVID-19 vaccine development strategy, therefore merit consideration. That would involve initiating long-lead-time substantive preparations for deployment concurrently with scientific evaluation, but not committing to full operational deployment of SRM capability until it has been adequately assessed with regard to its effectiveness and risks. By that or other means, the prioritization of SRM should be aligned with its unique precautionary role.