https://www.pnas.org/doi/10.1073/pnas.2401801121
*Authors* Anthony Harding, Gabriel A. Vecchi, Wenchang Yang, and David W. Keith *December 17, 2024* https://doi.org/10.1073/pnas.2401801121 *Significance* Solar geoengineering (SG) can cool the climate—the hard question is how its risks compare with its benefits? Using climate model simulations of idealized SG and data-driven of temperature-attributable mortality, we estimate that, in a world 2.5 °C warmer than preindustrial, 1 °C of global-average cooling by SG reduces mortality by over 400,000 deaths annually by 2080, with a possible range from −1.2 million to 2.7 million deaths annually. Mortality decreases in many hot, poor regions and increases in some cold, rich regions. We estimate the mortality benefits of reducing temperatures outweigh risks from air pollution and from ozone loss by 13 times for our central estimates, with a 61% probability the benefits exceed the risks. Uncertainty remains significant, highlighting the need for further research on SG’s trade-offs. *Abstract* Decisions about solar geoengineering (SG) entail risk–risk tradeoffs between the direct risks of SG and SG’s ability to reduce climate risks. Quantitative comparisons between these risks are needed to inform public policy. We evaluate idealized SG’s effectiveness in reducing deaths from warming using two climate models and an econometric analysis of temperature-attributable mortality. We find SG’s impact on temperature-attributable mortality is uneven with decreases for hotter, poorer regions and increases in cooler, richer regions. Relative to no SG, global mortality is reduced by over 400,000 deaths annually [90% CI: (−1.2 million,2.7 million)] for cooling of 1 °C from 2.5 °C above preindustrial in 2080. We find no evidence that mortality reduction achieved by SG is smaller than the reduction from equivalent cooling by emissions reductions. Combining our estimates with existing estimates of sulphate aerosol injection direct mortality risk from air quality and UV-attributable cancer enables the first quantitative risk-risk comparison of SG. We estimate with 61% probability that the mortality benefits of cooling outweigh these direct SG risks. We find the benefits outweigh these risks by 13 times for our central estimates, or 4 deaths per 100,000 per 1 °C per year [90% CI: (−11,23)]. This is not a comprehensive evaluation of the risk–risk tradeoffs around SG, yet by comparing some of the most consequential impacts on human welfare it is a useful first step. While these findings are robust to a variety of alternative assumptions, considerable uncertainties remain and require further investigation. *Source: PNAS* -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/geoengineering/CAHJsh9-VmNUmt3-QQ2LPLdHyo6-HS01CBgGGpf%3DVjckKj7_DDQ%40mail.gmail.com.
