Emperor penguins are not currently categorized as 'threatened' by the IUCN Red List, but they should be, according to biologists who study the species. They expect that at least 2/3 of Emperor colonies will have lost at least 50% of their populations by the end of the century because of changes in the sea ice caused by global warming.
Why does sea ice matter so much to penguins? It's not as if Antarctica itself will melt, but sea ice cover needs to be just right because too much of it makes for longer trips for the penguins when they go out to find food for their offsprings (their colonies are already 50–120 km/31–75 miles from the open sea), and too little reduces habitat for krill, an important food source for Emperors.
Right now, Emperor penguins are classified as 'near threatened' by the IUCN Red List and are being considered for inclusion to the U.S. list of endangered species under the US Endangered Species Act.
Via The Telegraph