This primer introduces solar radiation modification (SRM) to Canadian environmental non-governmental organizations (ENGOs) and policymakers, situating the topic in the context of accelerating climate timelines, Canada's own emissions shortfall, and growing international attention to SRM governance following reports from the UN Environment Programme, the Climate Overshoot Commission, and others. The analysis focuses on stratospheric aerosol injection (SAI), the method that holds the most promise and dominates current policy conversation and applies a risk-risk framework to weigh the risks of SRM deployment against the risks of continued climate change without it.
Key findings
- SRM is not a substitute for emissions reductions or carbon removal. In any SRM scenario, continued decarbonization and deployment of carbon removal are required to avoid the long-term risks of dangerous climate change.
- SAI offers a speed advantage no other intervention can match. It is the only climate intervention capable of cooling the planet within one to two years, with potential benefits including fewer extreme heat events, slower ice melt, and reduced sea-level rise.
- The cost of SAI is low enough that governance cannot be left to chance. Annual SAI costs that could reduce global temperatures by 0.5°C to 1°C are estimated in the tens of billions (US$), compared to roughly US$9.2 trillion per year to fully decarbonize the global economy, putting deployment within reach of individual nations.
- The principal risks are design- and governance-driven. Termination shock, moral hazard, and equity concerns depend on how SRM is deployed and governed, while known biophysical risks include modest ozone loss, regionally concentrated acid deposition, and altered precipitation.
- Risks and benefits are not evenly distributed. Regions most vulnerable to climate change, including the Global South and Indigenous communities, stand to gain the most from SRM's cooling effects while also facing disproportionate exposure to its side effects. Any deployment decision would also bind future generations to its ongoing maintenance.
- Key uncertainties remain in agricultural, ecosystem, and regional precipitation impacts. These knowledge gaps are grounds for continued research, not for avoiding the topic altogether, since restricting inquiry only preserves uncertainty rather than resolving it.
These dynamics help explain why SRM has moved from a fringe scientific topic to an active subject of international governance discussion, and why Canadian ENGOs and policymakers need a clear understanding of its methods, benefits, and risks. Current emissions trajectories mean there is no risk-free path forward, and declining to engage with SRM will not prevent decisions on its governance and deployment. It will only ensure those decisions are made without meaningful Canadian input.
