A simple experiment can be done to demonstrate this fact. A beaker filled with water ice will maintain its temperature near zero-degrees Celcius when placed over a bunsen burner. Not until all the ice has melted will the water temperature begin to rise sharply. I'm proud to say I did this experiment in grade 7 and still remember doing it. :-)

That said, it is probably the arctic ice pack that is most important for maintaining moderate global temperatures, since all that ice is immersed in water, exposed to currents. By contrast, much of the ice in the antarctic is sitting on land. Maybe I'm wrong here, but I don't think so.

There was a Chemical Engineer on Daily Planet science show (Discovery Channel) within the last couple days, explaining a plan to drive salty ocean water over sheets of existing ice during warmer times of year (perhaps with wind power). He predicted that the net effect would be greater ice buildup in the winter, since the water would be pre-cooled. It has been stated elsewhere as well that glaciation is influenced most strongly by how much snow remains on the ground in the summer, NOT by how much is deposited in the winter.

Interesting indeed. There may be something we can do about Global Warming, if it is found to be particularly threatening to human existence.