Sulfur, soot, and salt tracks: How good are ship tracks as analogues for marine cloud brightening? - Preprint

[Geoengineering News]

https://essopenarchive.org/doi/full/10.22541/essoar.176804689.91545166

Authors: Michael Diamond

10 January 2026

Abstract

Aerosol-cloud interactions exert a strong but highly uncertain negative radiative forcing, masking current greenhouse gas-driven warming and obscuring our ability to estimate future warming as well. ”Natural experiments” like ship tracks have been identified as a promising means of constraining aerosol effects on clouds; however, questions remain about the extent to which cloud adjustments observed in ship tracks generalize to other pollution effects. At the same time, inadvertent aerosol perturbations like ship tracks have inspired proposals to offset global warming impacts with deliberate aerosol cooling [e.g., marine cloud brightening (MCB)]. Ship track aerosol are a mixture of carbonaceous material and sulfate, but changes in fuel composition due to international regulations have shifted aerosol composition from larger sulfate-coated to smaller soot-dominated particles. There is currently a debate in the literature about whether reduced cloudiness observed in some ship tracks is due to cloud adjustments to aerosol-driven microphysical perturbations or to aerosol absorption, which is negligible for sea salt (as would be used for MCB). Through satellite observations both before and after these regulations went into effect and large eddy simulation modeling of cloud adjustments under sulfur-dominated, soot-dominated, and salt ”tracks”, we test the hypothesis that ship tracks observed in the historical record are good analogues for what salt tracks would behave like under MCB. If there are large differences between sulfur and salt tracks in particular, then current knowledge based on satellite imagery and field measurements of ship tracks would need to be interpreted cautiously for the case of MCB and may indeed underestimate efficacy, with implications for the merit of small-scale outdoor perturbative studies focusing on salt tracks in particular.

Source: Authorea