In response, an international team of researchers, led by the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR), has released a set of recommendations for evaluating proposals involving stratospheric aerosol intervention (SAI)-a technique involving the injection of sulfur dioxide into the stratosphere. The published guidelines also suggest criteria for discontinuing projects that face insurmountable scientific, technical, or societal challenges.

"The goal is to work toward an assessment that can be used to identify the most feasible and legitimate scenarios, based on both how much they reduce natural and societal risks as well as any unwanted side effects," explained NSF NCAR scientist Simone Tilmes, the lead author. "If society were to ever consider implementing SAI, it is imperative that we provide the best possible scientific understanding to policy makers and the public."

The research, funded by NSF and NOAA, has been published in 'Oxford Open Climate Change'.

Once sulfur dioxide is injected into the stratosphere, it forms sulfate aerosols that reflect sunlight. Studies utilizing computer models and data from past volcanic eruptions have demonstrated that these aerosols could cool the planet similarly to a significant volcanic event.

Such interventions could provide cooling for decades or even centuries, potentially giving humanity more time to reduce atmospheric greenhouse gas concentrations. However, previous research has also underscored the risks of SAI, including potential disruptions to the stratospheric ozone layer and changes in global precipitation patterns.

Given that SAI cannot fully counteract the effects of greenhouse gas emissions, Tilmes and her co-authors stress the importance of a well-rounded understanding of both the benefits and risks. They call for a research and governance framework that includes fair representation from both the Global South and North to oversee the development of SAI research and technology.

"Research on various solar geoengineering methods has been ongoing for a few decades now, but there hasn't been a formal assessment collating all the information in one place suitable for policy makers and the public," said NOAA scientist Karen Rosenlof, a co-author of the paper. "It's time for such an assessment to occur, covering the criteria described in this paper, and repeated on a regular basis."

The paper outlines eight criteria for evaluating SAI research:

1. Technical and economic limitations 2. Cooling potential 3. Ability to meet climate objectives 4. Infrastructure for monitoring, detection, and attribution 5. Large-scale and regional climate response 6. Impacts on human and natural systems 7. Societal risks 8. Mitigation of risks through governance

The paper advocates for the publication of assessment reports on SAI developments every few years, ensuring global participation. These criteria are also relevant to other solar radiation modification proposals, such as marine cloud brightening.

"The goal of these criteria is to promote optimal approaches from a climate perspective while carefully weighing the benefits and risks and making sure to include the perspectives of underrepresented groups and the Global South," Tilmes added.

Research Report:Research criteria towards an interdisciplinary Stratospheric Aerosol Intervention assessment

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