The world’s largest seasonal event is the change from summer to winter ice in Antarctica. Every year a magical event happens largely unnoticed by the general public. When the summer comes to an end, the already low Antarctic temperatures drop even further and start a process that is truly astonishing. When the water temperature drops roughly below a negative 1.7 degrees Centigrade the ocean starts freezing over despite its salty waters. By the end of the Antarctic summer, only about 3 million square kilometres (1.1 million square miles) of sea ice remain, largely in the Weddell Sea, in the Amundsen Sea off Ellsworth Land, off the probably windiest place on Earth - the George V. Coast and around Enderby Land. But during this world’s largest seasonal event, the ice undergoes a change in area from 3 million square kilometres to up to 18 million square kilometres (6.9 million square miles) in the winter. Unlike the Arctic—an ocean basin surrounded by land—the Antarctic is a large continent surrounded by an ocean. Because of this geography, sea ice has more room to expand in the winter. But that ice also stretches into warmer latitudes, leading to more melting in summer. Considering the permanent ice cover of the continent al year-round of about 14 million square kilometres (5.4 million square miles) this means that the total ice cover doubles from summer to winter. In early spring the sea ice breaks up and retreats back to roughly 3 million square kilometres again.