Sea level is on the rise. Since 1900, it's gone up an average of eight inches around the world, due to global warming. And by 2100, it will be higher still -- maybe as high as six-and-a-half feet above 1992 levels. That would put the homes of 7.8 million Americans at risk of being flooded.
Sea level rise is happening for two reasons. First, water expands as it warms. So the ocean is literally swelling and has nowhere to go but up. Second, more water is pouring into the sea as the ice on mountaintops and ice sheets in Greenland and Antarctica keep melting.
Scientists don't know exactly how much the sea will rise and by what date because they don't really know how much and how quickly ice will melt and slide into the sea. The recent draft of the National Climate Assessment (NCA), states that by 2100 the increase in sea levels could be as little as another eight inches, or as much as six-feet-seven inches - with two intermediate projections.
In this graphic, we took each of the four NCA projections and tied them to the population currently living within that elevation to illustrate the possible impact.