What it tries to imitate
Large volcanic eruptions cool the planet temporarily by forming reflective sulfate aerosols in the stratosphere. Proposed deployment would reproduce part of that effect deliberately and repeatedly.
What models agree on
Sufficient aerosol loading could lower global temperature and reduce some heat extremes. The cooling could begin relatively quickly and is technically more direct than removing hundreds of billions of tonnes of carbon dioxide.
What it cannot repair
It does not remove greenhouse gases, stop ocean acidification or perfectly reverse regional climate change. Temperature, rainfall, sunlight and atmospheric circulation would respond differently from a world without excess carbon dioxide.
Side effects and uncertainty
Potential effects include changes in precipitation, stratospheric heating, ozone chemistry, diffuse sunlight and ecosystems. Particle size, aggregation, materials and injection location affect outcomes, and global deployment has never been tested.
The termination problem
If strong cooling masked high greenhouse-gas forcing and deployment stopped abruptly, temperatures could rebound rapidly. Redundant systems might reduce accidental interruption, but political collapse, conflict or deliberate withdrawal cannot be modelled away.
Who controls the thermostat?
The central problem is governance: who chooses the target temperature, compensates harmed regions, monitors compliance and decides when to stop. Unilateral action could alter risks across borders.
Research versus deployment
Studying models, volcanic analogues and tightly governed small experiments is not the same as endorsing deployment. Knowledge can reduce uncertainty while emissions cuts remain the fundamental response.
Research record
Kravitz & MacMartin (2020), uncertainty and confidenceHack et al. (2025), engineering and logisticsPotentially powerful, inherently incomplete
Direct answer: Stratospheric aerosol injection could probably reduce global average temperature, but no deployment could restore the original climate or replace emissions cuts. It would create a novel climate with regional winners, losers, uncertainties and a long-term political commitment. “Safely” cannot yet be guaranteed.
Solar geoengineering may one day reduce some climate harms, especially during an emergency, but it cannot make continued emissions safe. Its physical effects, distributional consequences and governance risks mean it should be treated as a possible supplement—not a substitute for mitigation and carbon removal.