EC-08. Physical science checkpoints and exit ramps for marine cloud brightening research: What to study, when to stop?

Marine cloud brightening (MCB) is a proposal to offset some effects of global warming by seeding clouds with salt particles. This would produce brighter clouds and more reflection of sunlight back to space, cooling the Earth. Although there is a consensus that reducing greenhouse gas emissions is the most important step toward combating climate change, some scientists and policymakers have proposed that "solar climate intervention" proposals like MCB may be desirable to limit the effects of warming while other policies scale up. However, there are currently no formal governance structures determining how research into MCB should proceed, raising the risk of an unbalanced or misguided research portfolio. We propose that there exist six physical science "checkpoints" that must be addressed for MCB to be viable within the broader portfolio of climate policies. Each checkpoint is associated with an "exit ramp" that would discontinue the MCB research program if taken. For example, one checkpoint is how MCB would affect large-scale precipitation patterns. An exit ramp might be taken if it were found that MCB would pose an unacceptable risk of severe drought to a vulnerable region like the Amazon. Other checkpoints include the ability to generate particles of the proper size to produce the desired cloud responses and how marine ecosystems and coastal communities may be affected. Expertise in engineering, ecology, social science, and ethics as well as consultation with relevant stakeholders will also be necessary to assess the checkpoints and determine if an exit ramp should be taken.