"On really hot days, penguins are gasping for air", states Antarctic historian Dave Burkitt. Nearly 90% of glaciers here are retreating and ice shelves are collapsing at an alarming rate. With less ice available, seals have moved inland, where they disrupt nesting birds and damage plants. "The continent warming opens up the door to the introduction of many species", explains biologist Gary Miller. "That's our immediate concern." In 1914, the explorer Ernest Shackleton set out to explore Antarctica on foot. Comparing pictures of his voyage with the situation there now reveals the scale of changes.