"The problem is very serious. Antarctica and the Arctic are the most threatened regions from climate change," Juan Casavelos, WWF's Antarctic Climate Change Coordinator, said on Thursday.

"In the Antarctic Peninsula, the temperature has risen 2.5 deg C in the past 50 years, which is five times faster than the global average," he told Reuters from Barcelona, Spain, where the report was released at this week's International Union for Conservation of Nature congress.

Global temperatures have already risen on average by about 0.6 deg C since the Industrial Revolution, mainly through the burning of fossil fuels.

The report said unless nations slash carbon emissions, the world would warm by an average 2 deg C in less than 40 years.

But temperatures near the Poles have already risen much faster, leading to dramatic melting of glaciers on the Antarctic Peninsula, off the bottom of South America, and sea ice at the North Pole.

"The situation is quite critical because in the past 50 years, the emperor penguin population has decreased by 50 percent in all of Antarctica," Casavelos said.

On the Antarctic Peninsula's northwestern coast, Adelie penguin numbers have dropped dramatically over the past 25 years, WWF's report said, calling for rich nations to agree to steep cuts in greenhouse gas emissions in UN-led climate talks.

"Fifty percent of the colonies of the iconic emperor penguin and 75 percent Adelie penguin colonies face marked decline or disappearance if the global temperature is allowed to rise 2 deg C above pre-industrial levels," the report said.

"Under 2 deg C global warming and the projected decrease in sea ice thickness and increase in open water area, emperor penguins will find it increasingly difficult to find new nesting areas," it said.

With less sea ice, Adelie penguins could be pushed further south but this could hamper their hunts for food during the dark winter months because they needed at least a few hours of daylight to find food, the report said. (Editing by Sanjeev Miglani)