Sea level rise is an indicator that our planet is warming. Much of the world's population lives on or near the coast, and rising seas are something worth watching. Sea level can rise for two reasons, both linked to a warming planet. When ice on land, such as mountain glaciers or the ice sheets of Greenland or Antarctica, melt, that water contributes to sea level rise. And when our oceans get warmer - another indicator of climate change - the water expands, also making sea level higher.