Alaska's Prince William Sound is littered with icebergs calved from the Columbia Glacier, a few miles away. The Columbia ends in a tongue of ice that has retreated nine miles (14 kilometers) since 1980, shedding 25 cubic miles (104 cubic kilometers) of ice into the sound. The accelerating breakup of glaciers and ice sheets, if it continues, could raise global sea level by several feet over the next century.