I think you mean what happens if the sea-water loses its salinity! It will have disastrous effects to our Ocean habitat (97% of all life lives in oceans) and would causes quite pertinent changes to climate, more than humans can handle. read more
It then becomes a big reservoir of fresh water in which almost all marine plants, sea weeds corals to all marine fish including all invertebrates would die & if it happens in a short time, it would increase bacterial action drawing substantial amount of Oxygen that it could first lessen Oxygen values in the world. read more
Since water evaporating from the sea doesn't take the salt with it anyway, the weather wouldn't be very different. In other words, i don't think that the oceans' salt content plays much part in the Earth's weather, because i don't think there's much salt in the atmosphere. read more