Over the past few years, a large fracture has grown across a large floating ice shelf on the Antarctic Peninsula. The world is watching the ice shelf, now poised to break off an iceberg the size of Delaware into the ocean.It’s not a new phenomenon; this “thumb” of Antarctica, which juts out into the stormy Southern Ocean, has lost more than 28,000 square kilometers of floating ice — almost as large as Massachusetts — over the past half-century. This has included the complete disintegration of four ice shelves, the floating extensions of glaciers.