most of the worlds water just so happens to be at around 2~4°C, which is where water density is the highest, warming or cooling a bit causes it to expand, so just maybe it warms up a bit, and the total increased volume is enough to flood, everything we want dry.
Oh ya, we are on track for the warmest and most ice free artic summer ever.We just finnished the warmest and most ice free winter, so, ya, right.
https://nsidc.org/sea-ice-today
The average temperature of all water in the ocean is approximately 3.5° C, but I think most of the warming would be contained to surface waters which averages around 17° C. A bigger issue decreased density of seawater would probably just be melting ice
