What Is SRM?

Proposed SRM technologies aim to cool Earth by reflecting solar radiation away from the planet’s surface or by allowing heat to more easily escape the atmosphere. SRM deployment is intended to complement, not substitute for, existing climate mitigation and adaptation techniques.7
 

Proposed SRM Technologies:

• Stratospheric Aerosol Injection (SAI) uses high-altitude airplanes to spray gaseous precursors of reflective particles into the stratosphere, where they reflect a fraction of incoming solar radiation.8 SAI mirrors the cooling effect of volcanic eruptions, drawing inspiration from the 1991 eruption of Mt. Pinatubo, which cooled global surface temperatures 0.2–0.6°C in the year following the eruption.9 SAI is highly controversial due to its potential unintended consequences, fears that its adoption will lead to the deprioritization of climate mitigation, and its conflation with chemtrail conspiracy theories.10
• Marine Cloud Brightening (MCB) enhances the ability of tropospheric marine clouds to reflect solar radiation by “seeding” them with saltwater particles. MCB is already being tested as a method to increase cloud reflectivity at Australia’s Great Barrier Reef.11
• Mentioned less frequently in the technical literature (and thus deemed beyond the scope of this primer) are cirrus cloud thinning, surface albedo enhancement, and space-based radiation reflection.12