Solar geoengineering, the controversial idea of deliberately intervening in the climate system to counteract global warming, has long lived mostly in computer simulations.
The concept is inspired by volcanic eruptions, which have historically cooled the planet by blasting sulfur dioxide into the stratosphere, where it converts into sunlight-scattering particles. Hundreds of studies suggest a human-made version could work efficiently, at least within climate models.
But a growing group of researchers is now moving beyond simulations to tackle the practical engineering questions: what aircraft could actually reach the stratosphere, what materials should be released, how they’d be dispersed, and what monitoring infrastructure would be needed to know if any of it worked.
Much of this work is happening at the University of Chicago’s Climate Systems Engineering Initiative, launched in 2024 under prominent geoengineering researcher David Keith.
One project involves designing an entirely new type of uncrewed aircraft, with massive wings built to reach roughly 20 kilometers up, high enough to release reflective materials into the thin stratospheric air. A nonprofit called Reflective has separately mapped out just how much infrastructure a real deployment would require, including retrofitted aircraft, new airports, shipping routes, chemical processing facilities, and stratospheric monitoring instruments, concluding that even a modest early program could take a decade and around $35 billion to get running.
Not everyone believes this research should be happening at all. Critics warn that simply building momentum in engineering studies makes eventual real-world deployment more likely, regardless of how many uncertainties remain. Some argue the deeper danger isn’t technical but political, since geoengineering could never be deployed or governed in a way that’s fair to everyone. Cooling the planet by even a modest average amount could help some regions while harming others, potentially disrupting monsoons, agriculture, or disease patterns, and critics worry that whoever holds the wealth and power to deploy such a system would tune it for their own benefit rather than the world’s. Others focus on the “moral hazard” risk: that simply advancing the research, even on paper, could be used by fossil-fuel interests to argue a cheaper climate fix is coming, easing pressure to cut emissions.
Keith rejects the idea that this kind of open academic research should face special restriction, arguing that the potential to reduce catastrophic suffering from climate change means the bar for limiting it should be very high. He and his colleagues stress that the current work isn’t about building deployable hardware or restarting stratospheric field experiments, like Harvard’s abandoned SCoPEx project, but about understanding what a future deployment would require if a nation ever decided to pursue one. Still, Keith’s own position has shifted over the years: he now argues the evidence suggests a carefully managed, slow, well-monitored early deployment would likely do more good than harm, and says he’d personally vote yes if there were a global referendum on starting.
The debate is unfolding as solar geoengineering moves beyond purely academic conversation, with a handful of startups already testing related technologies. Researchers within the field mostly insist they aren’t advocating for its use, but are simply trying to give policymakers and the public a clearer, more realistic picture of both the benefits and risks before any decision is made. Whether that clarity ultimately makes deployment more responsible, or simply more likely, remains one of the field’s central unresolved tensions.