Published: January 2006
Did You Know?
In Did You Know? the National Geographic magazine team shares extra information we gathered to expand your knowledge of our featured subjects.

We've all heard about increased ice melt at the Poles because of global warming and how it is causing sea level to rise everywhere, but the problem is not just that polar ice caps are melting. Nearly 50 percent of the cause of sea level rise is due to a phenomenon known as thermal expansion—as water heats up, it expands. This means that there is not an increase in water, but rather, the existing water takes up more volume. And where is this excess water headed? Some of the consequences of sea level rise include loss of coastal wetlands, barrier islands, and a greater risk of flooding in coastal communities.

—Nora Gallagher