Australia's Great Barrier Reef could be "functionally extinct" within decades, warns a leaked portion of a major United Nations report on climate change.

A confidential draft of the report, prepared by the Intergovernmental Panel on Climate Change (IPCC), was leaked to Australia's The Age newspaper.

The Great Barrier Reef is shown in 1997.
(World Wide Fund for Nature/Associated Press)

It warns warmer, more acidic seas could severely bleach coral in the world-famous reef as early as 2030. Recovery from such bleaching could take decades, the draft report warns.

However, if seas continue to warm, the coral could be killed outright, says the report.

The leak provides the first glimpse of Friday's initial report, which is expected to contain the strongest language yet about the possibility human-caused greenhouse gas emissions have had an impact on global warming.

The initial report — authored by over 2,000 scientists — will be followed by subsequent sections to be rolled out throughout the year, including examinations of climate change impacts and solutions to climate change.

A draft copy of the climate change impacts section, due out in April, contains an entire chapter on Australia, said The Age.

Along with the reef warning, the report says snow could disappear from Australia's southeastern alps, while water inflows to the country's main agricultural region could decrease by as much as 25 per cent by 2050.

Spanning 2,000 kilometres, the reef is one of Australia's top tourist destinations, generating close to $6 billion US per year and tens of thousands of jobs, said the newspaper.

'Important and urgent'

In anticipation of the report's findings, top UN officials have already met to discuss an emergency international summit on climate change later in the year, an official close to the talks said.

UN Secretary General Ban Ki-moon met with Achim Steiner, the executive director of the UN Environment Program, to discuss the potential summit and Ban is said to be considering the idea, an official said.

"Climate change is one of the most important and urgent agendas that the international community has to address before 2012," Ban told reporters on Tuesday.

Kenya has been suggested as a possible location for a summit later in the year.

With files from the Associated Press