…that is if you forget that they are gas-guzzling uber machines spewing carbon dioxide.
the first indirect effect, whereby an increase in aerosols causes an increase in droplet concentration and a decrease in droplet size for fixed liquid water content (Twomey, 1974), and the second indirect effect, whereby the reduction in cloud droplet size affects the precipitation efficiency, tending to increase the liquid water content, the cloud lifetime (Albrecht, 1989), and the cloud thickness (Pincus and Baker, 1994).
These ship-caused clouds can reflect light. Locally this can be up to 100 watts per meter squared, for comparison the flux at the top of the atmosphere is around 340 watts per meter squared. Obviously, this is fairly large effect locally and potentially problematic given the thousands of ships that clog the ocean’s shipping lanes (below). What has not been quantified until now is how these clouds affect the global albedo (the extent to which the earth reflects light, defined as the ratio of reflected to incident electromagnetic radiation). Schreier et al. using satellite imagery, algorithms to extract ship clouds from the images, and modeling, estimate the impact on global albedo. Overall their analysis show that the effects are relatively small compared to the total anthropogenic effect (0.4 to 0.6mW/m2 versus 0.6 to 2.4 W/m2).