Jim Franke spreads aircraft renderings across his desk at the University of Chicago, showing uncrewed planes designed to fly 20 kilometers above Earth. These massive-winged aircraft would operate in the thin stratospheric air, releasing materials to reflect sunlight and artificially cool the planet. Franke, a research assistant professor, leads practical engineering work through the Climate Systems Engineering Initiative, which launched in 2024 under David Keith.

The concept mimics volcanic eruptions that historically cooled Earth by scattering sunlight. While climate models suggest geoengineering could work quickly, they overlook critical engineering hurdles. No existing aircraft can carry payloads to required altitudes, and researchers haven't mastered how to disperse materials into effective reflective aerosols. The shift from simulation to hands-on design represents a new phase in solar geoengineering research.

Reflective, a San Francisco nonprofit, mapped out what a moderate deployment scenario would require. Their 2035 timeline envisions small-scale releases near the poles, gradually scaling to global cooling of 0.5°C. This approach targets regions where the stratosphere sits at just seven kilometers, making initial flights feasible with modified existing aircraft. However, polar deployment creates uneven cooling effects, leaving tropical regions—already most vulnerable to climate change—less protected.

Critics like Jennie Stephens argue increased research momentum raises deployment risks despite unresolved dangers. Proponents counter that practical work reveals true costs and risks, potentially enabling safer implementation. Whether this engineering advances understanding or accelerates adoption remains contentious, but the technical groundwork continues regardless.