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Unintended Weather Consequences. SRM’s potential effects on weather and precipitation patterns are poorly understood. Though deployment might improve surface temperatures in some areas, it might negatively impact temperatures and weather patterns elsewhere in ways that are difficult to predict.49

Localized Effects. Even if SRM stabilizes and cools global temperatures, devastating weather patterns will still occur, and global temperatures will still fluctuate.50

Termination Shock. Unlike emissions reduction, which targets the root cause of greenhouse gas accumulation, SRM targets only one symptom of emissions—global mean surface temperature—and does so without reducing overall emissions. If SRM (SAI, in particular) is used for a long time and rapidly terminated, global temperatures will rapidly increase above pre-SRM temperatures if greenhouse gas emissions are not reduced during SRM’s deployment.51

Opportunity Cost. While SRM is less expensive than the cost of unchecked climate change, it will almost certainly compete with funding for emissions reduction strategies, such as investments in energy efficiency and renewable energy. SRM may also compete with funding that supports research and deployment of carbon sequestration technologies, including reforestation, grassland management, and carbon capture and storage.

Moral Hazard. Some fear that reliance on SRM technologies will disincentivize emissions mitigation, which would increase baseline global temperatures. Additionally, SRM deployment could appear to relieve richer, more industrialized countries of their responsibility for carbon emissions and climate change.52

Climate Equity and Justice. SAI’s potential to change precipitation patterns unintentionally or to warm certain regions while cooling others raises questions about who should decide when, where, and for how long SRM technologies are deployed, which risks are acceptable, and how to monitor deployment, resolve conflicts, and compensate communities that are negatively impacted.53 Because nearly all SRM research, deployment, and governance efforts are based in the Global North, some have expressed concern that SRM is inherently unjust, as no currently viable governance model offers Global South stakeholders decision-making power. However, some argue that SRM deployment in the Global South could be a viable climate justice mechanism for communities that are heavily affected by climate change despite their lack of responsibility for most global emissions. The Developing Country Governance Research and Evaluation for SRM (DeGReES) Initiative started in 2010 and is an NGO dedicated to putting the Global South at the center of the SRM conversation. It currently funds 170 researchers on thirty-seven SRM projects in the Global South.54

Health and Social Concerns. Little research has been conducted on how SRM techniques might impact human health.55 The U.S. EPA’s website warns of SAI’s potential to cause acid rain and respiratory illness.56 Research also suggests that SAI deployment could change which regions are most susceptible to diseases like malaria, increasing infection rates.57 In the United States, conflation of SRM with the chemtrails conspiracy theory has led to concerns on social media and in the halls of Congress about ill-intentioned actors releasing chemicals into the air for nefarious purposes, though these claims have not been substantiated.58

Unintended Ecological Consequences. Little to no research has been conducted on how SRM’s effects (including more diffuse sunlight, unpredictable temperature and precipitation changes, and the decoupling of atmospheric CO₂ concentrations from temperature) would affect plants, animals, and microorganisms.

Additional potential risks include drought in Africa and Asia, ozone depletion leading to enhanced ultraviolet radiation at the surface, lowered solar electricity generation, degradation of passive solar heating capacity, effects on airplanes and airplane passengers flying in the stratosphere, impacts on satellite remote sensing, negative effects for terrestrial optical astronomy, more sunburns, and less blue sky.59