My physics book gives a coefficient of volumen expansion, for water, of 210e-6 / degree Celsius. This might be insignificant in many cases. Now, if you assume that on the ocean, on the average, is 2.5 km. deep (not sure about this figure), that would mean an expansion of 2500 meters * 210e-6 = about half a meter, for an average temperature increase of 1 degree Centigrade. I am not sure how significant this would be, but just guessing, I would have supposed it to be less than that.

>I have read somewhere that the volume of water coming from melted ice is negligible in the raising of sea level. The main factor of raising is caused by the water temperature.
>In a glass of water the difference of volume cannot be significant for a couple of degree change, but for the sea that represent some meter!
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>The main effect of the melting of the polar ice, is that the ice is reflecting a certain amount of sun shining (albedo). If the ice surface shrink, the water will absorb more sunshine and heat that will accelerate the shrinking and so on...