As evidence for severe impacts of global warming continues to accumulate, the possibility of averting the worst effects of climate change through climate intervention (CI) is a topic of increasing scrutiny and debate. The common goal of these CI proposals is to cool the climate by deliberately modifying the solar (shortwave) or terrestrial (longwave) radiation pathways in the Earth’s atmosphere, aiming to reduce the worst impacts of rising global temperatures, in addition to reducing greenhouse gas (GHG) emissions. Marine Cloud Brightening (MCB), one such CI proposal, focuses on enhancing the reflection of solar radiation by warm (liquid containing) marine clouds through the deliberate injection of sea salt particles into these clouds.

The Overview Our papers lay out physical science knowledge and gaps on MCB and discuss research needed to assess the viability and risks of MCB. In particular, we focus on How does it work, in theory? (underlying physical processes), Viability at scale, Feasibility-from nozzle design to large-scale deployment (the contingencies), and Risks-known and unknown associated with MCB proposals.

Marine cloud brightening proposals use ship-based generators to release haze droplets. In optimal conditions, these droplets are lofted into clouds by updrafts, modifying cloud microphysics by increasing droplet concentrations, suppressing rain formation, and extending cloud coverage and lifetime. The left side illustrates key aerosol, cloud, dynamics, and radiation processes in the marine boundary layer that underpin MCB in shallow liquid clouds. The strong coupling between these processes presents challenges and opportunities for understanding the effects of seawater haze injections. Figure is reproduced from Feingold et al. 2024 Science Advances.
An integrated view of MCB research. Laboratory facilities such as cloud chambers, together with observations at various scales, help improve the representation of physical processes in models. Parcel models, large eddy models, and cloud-resolving models inform global model activities to enhance the reliability of regional climate responses. The Earth view image is courtesy of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). Figure courtesy of Chelsea Thompson, NOAA/CSL.

  • J. Zhang and G. Feingold (2024): Physical Science of Marine Cloud Brightening: Knowledge and Gaps, in Topical Group on the Physics of Climate, American Physical Society, October 2024, pp. 1–4. (invited article)

  • G. Feingold, V. Ghate, L. Russell, et al. including J. Zhang (2024): Physical science research needed to evaluate the viability and risks of marine cloud brightening. Sci. Adv., 10(12), eadi8594. doi:10.1126/sciadv.adi8594