The sea ice around Antarctica melts and refreezes with the seasons, usually doubling the size of the continent by the end of winter. For most of 2023, about two million square kilometres has been missing in action—a record low. We’ve only been keeping satellite records of sea ice for 44 years, but the extent of the melt is “an alarming drop off the cliff” and very unlikely to be natural variability, says NIWA’s Natalie Robinson. “We’re essentially missing between seven and 10 New Zealands’ worth of sea ice.”

Some Australian researchers have even suggested the Southern Ocean is entering a new state of lower ice levels—a so-called “regime shift” with worldwide flow-on effects.

Sea ice reflects heat and absorbs carbon dioxide from the atmosphere. It controls how oceans distribute warmth, nutrients and oxygen across the planet. And the ice provides crucial habitat—from the algae and krill that live underneath and form the basis of the marine food chain to the penguins and seals that breed on its surface.

New Zealand is one of the closest nations to Antarctica, and our climate is strongly influenced by the Southern Ocean, says Craig Stevens, also from NIWA. “Some of these effects will be felt here first.”