Emperor penguins—the tallest, most iconic penguin species on Earth—have officially been classified as endangered after rapid population declines driven by vanishing sea ice.

The emperor penguin has been declared an endangered species as climate change pushes the icon of Antarctica a step closer to extinction, the global authority on threatened wildlife announced Thursday.

The impacts of climate change in Antarctica have put both the emperor penguin and Antarctic fur seal at risk of extinction, and both species should be considered endangered, a major international envi...