A California-based startup, Make Sunsets, is generating significant controversy with its novel approach to combating climate change: launching weather balloons filled with sulphur dioxide into the stratosphere to reflect sunlight and cool the planet. The company, co-founded by Luke Iseman and Andrew Song, sells "cooling credits" to customers for each gram of SO2 released, having already deployed nearly 65,000 grams via 90 balloons. This initiative, inspired by Neal Stephenson's science fiction novel *Termination Shock*, draws inspiration from the natural cooling effect observed following the 1991 Mount Pinatubo eruption. Research suggests that a half-degree Celsius reduction in global temperature could prevent hundreds of thousands of heat-related deaths annually.
Make Sunsets' methods involve filling high-altitude balloons with SO2, which, upon bursting in the stratosphere, converts to sulphuric acid, thereby reflecting solar radiation. The company maintains regular contact with leading scientists in the field, although it declined to disclose their identities. While the underlying science of stratospheric aerosol injection (SAI) is sound, according to experts like David Keith, a professor of geophysical sciences at the University of Chicago, the scale of the operation is currently minuscule. Keith estimates that at least a million tonnes of SO2 would be required annually to achieve a sustained half-degree cooling â a figure far exceeding Make Sunsets' current output. He also points out the inherent contradiction of using a pollutant (sulphur) to mitigate another pollutant (carbon dioxide).
The company's claim that one gram of SO2 offsets the warming effect of one tonne of CO2, derived from public statements by Keith and other researchers, has been described by Keith himself as a "very rough number" unsuitable as a business foundation. This highlights a core criticism levelled against Make Sunsets: the lack of rigorous scientific oversight and the potential for unintended consequences. Indeed, Keith's own research indicates that SAI on a sufficient scale could lead to thousands of premature deaths annually due to air pollution and increased skin cancer risks from ozone depletion.
The ethical and scientific implications of SAI are further debated by experts. Shuchi Talati, founder and executive director of the Alliance for Just Deliberation on Solar Geoengineering, acknowledges the potential of SAI but stresses the need for thorough research into its long-term effects on precipitation, weather patterns, public health, and biodiversity. Raymond Pierrehumbert, a physicist from the University of Oxford, argues that SAI is merely a temporary "Band-Aid" solution, masking the underlying issue of excessive atmospheric CO2. He highlights the catastrophic risk of "termination shock" â the rapid warming that would occur if SAI were abruptly ceased after prolonged use, a concept explored in Stephensonâs novel. Pierrehumbert is among hundreds of academics who have signed a non-use agreement calling for a global ban on SAI.
Conversely, David Keith and over 100 other academics have signed an open letter advocating for further research into solar geoengineering. While acknowledging the potential risks, they believe that computer modelling alone may suffice, removing the necessity for large-scale outdoor experiments. The United States and Canada, amongst other nations, are actively exploring the potential of geoengineering, though this research is met with considerable opposition.
Make Sunsets, though not conducting formal scientific research, has undeniably spurred public discourse on geoengineering. Professor Keith characterises the companyâs actions as "performance theatre," acknowledging its success in raising awareness, though ultimately uncertain about its effectiveness in shaping policy. Luke Iseman, while acknowledging the skepticism surrounding Make Sunsets, maintains that all available options should be explored to address the climate emergency, arguing that the current situation demands a bolder approach. He plans to continue expanding the project, aiming for larger-scale deployments. The debate surrounding Make Sunsets underscores the complex ethical and scientific challenges inherent in geoengineering, highlighting the urgent need for comprehensive research and carefully considered international policy before deploying such technologies.
