The quest to identify a new way to potentially counter one of the world's most widely discussed solar geoengineering proposals has taken a new, exciting turn - raising questions about how future climate interventions could be governed.
In a newly published modelling study, a team of scientists have found that a technique which they term Stratospheric Aerosol Scrubbing (SAS) could reduce the effectiveness of Stratospheric Aerosol Injection (SAI) – a hypothetical proposal to inject sulphur dioxide into the upper atmosphere to reflect sunlight back into space and 'cool' Earth.
Using a cutting-edge climate model, researchers found that injecting calcite particles into the stratosphere could trigger the growth of larger aerosol particles that fall out of the atmosphere more quickly.
In simulations, the approach reduced stratospheric aerosol levels by around 30-40% and cut the cooling effect of SAI by roughly one-third.
The findings represent the first detailed assessment of whether a climate intervention could itself be countered through a deliberate atmospheric intervention.
"Most solar geoengineering scenarios assume global co-operation. We challenge this assumption and show that counter interventions could prove an effective destabilization tool" says lead author Dr Anthony Jones, a Senior Lecturer at the University of Exeter.
Solar geoengineering remains one of the most controversial ideas in climate science. Supporters argue it could temporarily offset rising temperatures if emissions reductions prove insufficient. Critics warn it could create new environmental risks, geopolitical tensions and disputes over who controls the Earth's climate.
The new study examines a scenario in which a government, coalition or other faction opposes a solar geoengineering programme and seeks to weaken its impact. Researchers also considered cooperative scenarios in which countries might use aerosol scrubbing to help phase out geoengineering or respond to unexpected side effects.
The proposed technique works in a similar way to industrial pollution scrubbers used to remove contaminants from power-plant emissions. Rather than removing pollutants from smokestacks, however, atmospheric scrubbing would encourage reflective particles in the stratosphere to grow larger, making them less effective at reflecting sunlight and causing them to settle out of the atmosphere more quickly.
The researchers tested both short-term and long-term intervention scenarios. In a 20-year simulation, the cooling influence of solar geoengineering fell from -3.3 watts per square metre to -2.3 watts per square metre, representing a reduction of about 30%.
The authors stress that the study is an early proof of concept rather than a deployment proposal. Important uncertainties remain, including how the process might interact with atmospheric chemistry and stratospheric ozone.
