In winter, Arctic air is hazy with industrial pollutants from Europe and Asia trapped by weather systems, so more aerosols have little effect. In summer, though, when sea traffic increases, the air is clear and the research suggests a single vessel can affect cloud formation. This is true even with low-sulphur fuel, which is supposed to be more environmentally friendly.
The amount of cloud affects “radiative forcing,” how much is trapped and does not escape back to space, increasing the greenhouse effect.
The paper is here