From time to time I see clueless people writing that the melting polar sea ice increases sea level, and sometimes that it would decrease it. Fact is that it remains the same melting sea ice does not contribute to seal level rise. I am so glad someone made this video to demonstrate it, so I don’t have to:
The reason is that a floating piece of ice displaces exactly as much water as it weighs. It neither gains nor looses mass during melting, so the water from the ice replaces exactly as much as it had displaced.
The rise of the sea level expected from global warming comes from the melting ice on land, from the ice shields of Greenland and Antarctica, and to a lesser extent from the ice of mountain glaciers and thermal expansion. That ice is not floating on the oceans.
Update: rephrased, and added thermal expansion. Changes in italics.