Global warming is threatening the survival of four penguin species in the Antarctic, conservationists warned today.

A new report from WWF, published at the UN conference on climate change in Bali, has found that global warming is occurring five times faster in the Antarctic peninsula than the rest of the world, and threatening the survival of the emperor, gentoo, chinstrap and Adélie penguins that breed on the continent.

Melting sea ice is destroying precious nesting grounds where the penguins raise their young, while over-fishing is making food increasingly scarce according to the report, Antarctic Penguins and Climate Change.

"As the ice melts, these icons of the Antarctic will have to face an extremely tough battle to survive," said Emily Lewis-Brown, marine and climate change officer at WWF-UK. "One of the coldest environments in the world is actually seeing some of the fastest rates of global warming, and unless action is taken to reduce global CO2 emissions, the future of many Antarctic species looks bleak."

The Antarctic peninsula is warming five times faster that the average rate of global warming and the waters of Southern Ocean have become warmer as far down as 3,000m, the report found.

Sea ice is now covering 40% less area that it did 26 years ago off the west Antarctic peninsula.

This decrease has led to reduced numbers of krill, the main source of food for chinstrap penguins.

Some colonies of chinstraps have seen reductions in numbers of up to two-thirds because less food has made it more difficult for youngsters to survive, the report said.

The gentoo penguin has also seen numbers shrinking because it is increasingly dependent on the krill as its usual food sources have been depleted by overfishing, the report said.

And on the north-western coast of the Antarctic peninsula, populations of Adélie penguins have dropped by 65% in 25 years.

The report said the penguins had been suffering from scarcer food supplies and encroachment by gentoo and chinstrap penguins which were taking advantage of higher temperatures where warming has been most dramatic.

Scientists are concerned for the Adélie, which lives on sea ice but needs the ice-free land to breed, where they line their nests with pebbles that they often steal from their neighbours.

The emperor penguin, the largest in the world, has seen some of its colonies halved in the past century as warmer temperatures and stronger winds force them to rear their young on increasingly thin ice, the report said.

The WWF said that in recent years sea ice had broken off early and many eggs and chicks had been blown away when they were too young to survive on their own.

The environmental charity warned that the emperor penguin was the most vulnerable of the Antarctic bird and mammal species in the face of climate change, as it needs stable, land-locked sea ice on which to breed because it is too clumsy to climb over icy coastal slopes.

The WWF is calling for the Bali summit to agree a process which will lead to comprehensive and fair emissions reductions after phase one of the Kyoto protocol ends in 2012.

Lewis-Brown added: "The UN climate change summit underway in Bali must agree a process now which results in comprehensive, ambitious, and fair global emission reduction targets beyond the current phase of Kyoto which ends in 2012. It's vital that governments agree upon a clear, shared vision to keep global warming to less than 2C above pre-industrial levels."