The seas actually appear to be rising fast because the land is actually sinking in some places and rising in others. On the average, though, the global sea level is rising, sometimes at a much faster rate. We do not know yet how much of the rising sea level is caused by melting of glaciers, that add water to the oceans, or by expansion of the existing ocean water due to slow warming. Rising ocean levels would make hurricanes and other storms more dangerous. More than half the U.S. population lives within 50 miles of a coastline.
Sea ice reflects the sun's rays.
When the sun shines down onto the ice, it reflects the sunlight back into space away from Earth. The more sea ice there is, the more solar energy gets reflected back into space and the less heat stays on Earth. This causes the climate to become colder. The two largest ice sheets are in Greenland and Antarctica. If all this ice melted back into the ocean it would raise sea level by over 75 meters.