How do glaciers affect sea level rise?

Sea levels have risen and fallen throughout geologic history due to a myriad of natural processes, most notably the forming and melting of glaciers. Since the end of the last glacial peak, sea level has risen worldwide on average, but over the past 150 years, the pace of sea level rise has increased as ice melt has hastened and sea water has warmed and expanded.

But oceans aren't rising at the same rate everywhere. Some parts of the U.S. East Coast have experienced a faster rate of sea level rise than other places. During the twentieth century, sea level rose about a foot and a half near the Outer Banks in North Carolina and along the nearby Chesapeake Bay in Virginia. Yet New York City and Miami both saw only about a foot rise during that same time. And Portland, Maine saw only about half a foot of rise.

Glaciers are responsible for much of the global rise we see today. But past glaciers are also causing big differences in sea level rise from place to place.

Glaciers are rivers of ice. You’ll find them in places where snow falls in winter and doesn’t melt entirely in summer. Every year, a new layer of snow covers and packs down the old layers underneath. Over time, the weight of all that snow squeezes the bottom layers into a solid block of ice.

Glaciers are found on mountaintops or near the poles. They can vary from the size of a football field to an ice patch hundreds of miles long. Or they can be even bigger. Enormous glaciers cover Antarctica and Greenland. Glaciers of this size are called ice sheets.