Impacts of Stratospheric Aerosol Injection on Precipitation and High-Altitude Clouds: A Model Hierarchy Approach
Stratospheric aerosol injection (SAI) has been proposed as an effective way to cool the Earth by scattering a small portion of incoming sunlight. However, sulfate aerosols used in SAI also warm the lower stratosphere, potentially lowering the tropopause and altering cloud and aerosol processes that current climate models struggle to accurately capture. Our project focuses on three critical—and poorly understood—consequences of SAI:
- Global hydrological cycle – How much would SAI weaken precipitation by reducing radiative cooling in the troposphere?
- High-altitude clouds – How will anvil and cirrus clouds “sink, shrink, or brighten,” and what does that mean for Earth’s radiation budget?
- Upper-tropospheric aerosols – Will SAI suppress or enhance in-situ particle formation, and how will that affect and the supply of cloud-condensation nuclei?
To trace the impacts of SAI from individual cloud towers to the entire planet, this research will use a model hierarchy approach incorporating:
- Single-column radiative–convective models to uncover first-order thermodynamic and energetic controls on precipitation.
- Kilometer-scale cloud-resolving simulations to examine how stratospheric heating reshapes the life cycle and radiative effect of tropical high clouds.
- Global and super-parameterized general circulation models (GCMs) to integrate cloud-scale insights into a planetary framework and map regional hydrological shifts.
- Coupled aerosol-microphysics schemes to quantify the tug-of-war between reduced convective lofting, temperature-dependent nucleation, and sulfate-driven condensation sinks.
By testing each hypothesis across three experiment setups—solar dimming only, stratospheric heating only, and the two combined—and cross-validating across models, this work aims to deliver rigorous, process-based bounds on SAI’s ripple effects on precipitation, cirrus clouds, and aerosol formation.
