Introduction to the Governance of Solar Radiation Modification: Key SRM approaches and their governanceDouglas G. MacMynowski challenges Douglas MacMartin Mechanical & Aerospace Engineering, Cornell University 1 Mt. Pinatubo Resulted in 30Mt of 1991 sulfate aerosols in stratosphere Stratospheric Aerosol Injection (SAI): Could potentially do this with aircraft… Volcanoes caused global cooling by putting small particles 2 in the stratosphere Marine Cloud Brightening Ship tracks due to aerosols • Spraying salt-water into low clouds might cool • Cloud-aerosol interactions are poorly understood! • Doesn’t work everywhere: spatially heterogeneous forcing • BUT: could use for regional cooling3 Could cirrus cloud Cirrus Cloud cover be artificially reduced by Thinning seeding with efficient ice nuclei? Unseeded cirrus clouds Seeded cirrus clouds Solar Radiation Modification (SRM) • Reflecting sunlight would cool the climate Marine cloud – Space-based brightening – Stratospheric aerosol injection (SAI) (MCB) – Marine cloud brightening (MCB) – Surface • Could also enhance outgoing radiation – Cirrus cloud thinning (CCT) Stratospheric Aerosol Cirrus cloud Injection (SAI) thinning (CCT) 5 What is the role for SRM? Business as usual Cut emissions aggressively 1 CO2 removal (“CDR”) 3 2 Climate Impacts Climate SRM? Time Climate Model Simulations (of SAI) 1° warming from CO2 offset by 1° warming from CO 2 1° cooling from strat. aer. Temperature (perdegree) Precipitation (perdegree) MacMartin et al, JGR 2019 Some Key Governance Questions • How confident do we need to be? – Some uncertainty will not be resolvable • Who gets to decide? – Everyone is affected… whose voices are at the table? • How will decisions be made? • What happens if some people/places are harmed? – Or are perceived to be harmed? • How do you ensure this isn’t used as an excuse not to mitigate? – “Moral Hazard” or mitigation deterrence • How do you manage deployment over very long timescales? – Possibly centuries, and without any interruption Impacts would depend on how it is deployed SIMULATION 1 SIMULATION 2 Constant aerosol injection CHANGE IN Varying injection with time of year INDIAN PRECIPITATION • This makes it hard to talk about “the” impacts of SAI • Decisions aren’t just yes/no Not a substitute for mitigation Business as Cut emissions usual aggressively CO2 removal Climate Impacts Climate Solar geoengineering… Time 10.