The population of Antarctica's famous emperor penguins could fall by a third by the end of the century because of disappearing sea ice, putting them at risk of extinction, say researchers.
Writing in the journal
Nature Climate Change, scientists from Woods Hole Oceanographic Institution in the US state of Massachusetts say their findings justify protecting emperor penguins under the US Endangered Species Act - as it already does for polar bears.
They also call for marine reserves to be created to buffer the fish stocks that penguins need to survive.
"The population is declining. Unless something changes to stop that, the population will go into extinction," said Professor Hal Caswell, one of the study's authors.
Penguins are mainly at risk from climate change The melting of sea ice is reducing the supply of krill, the shrimp-like crustaceans that populate the Southern Ocean and are the penguins' main food source. Young krill feed off algae living in the sea ice. When the ice goes, so do the krill.
Changes in the ice around Antarctica might - in the short term - boost some of the emperor penguin populations, especially along the Ross Sea, the researchers said. Sea ice off the western coast of Antarctica has been on the increase, because of wind conditions and the break-up of glaciers.
But by 2100, all 45 known emperor penguin colonies of Antarctica will be on the decline because of loss of sea ice.
Other studies have raised the threat to emperor penguins under climate change, suggesting the animals, which grow to more than a metre high, are susceptible to rising heat.
Researchers from the University of Minnesota last week suggested some emperor penguin colonies might be able to migrate, and so adapt better to changing ice conditions than previously thought.
But the Woods Hole researchers said their study was the first to forecast a population decline across all of Antarctica. It also saw little scope for penguins to adapt to the changing ice conditions.
The researchers said the findings called for urgent measures to help the penguins survive - such as legal protection and the creation of marine reserves.
"Implementing a marine protected area in the Ross Sea could help buy time to avoid extinction and to put in place needed conservation and greenhouse-gas mitigation strategies," said Dr Stephanie Jenouvrier, lead author and a scientist at Woods Hole.