Even if scientists agreed that spraying seawater upwards from every ship would mitigate say 10 years of climate change, can you imagine world governments coming to an agreement to do it, and how to fund it?
You could maybe equate it to an equivalent amount of carbon capture and pay for it the same way. I'm not sure I'd agree with that, though, unless it was only paid at a lower rate than true carbon capture / reduction schemes.
Unlike CO2 which has been nicely stored away from the atmosphere for millions of years…
sulfur is both a greenhouse gas and a condensate for cloud formation
nature is full of examples where you can add more and more of a single factor and suddenly the effect will flip and contribute to the other direction, before reaching a further threshold and flipping the other way
it is not possible to make blanket statements like "Adding water to the atmosphere increases average temperature"
As I understand it, CO2 is one of the few factors that we can all agree is just straighforward, more CO2 more problems. But chaos is tricky, we can only simulate so much.