Billions of people will suffer water shortages and the number of hungry will grow by hundreds of millions by 2080 as global temperatures rise, scientists warn in a new report.
The report estimates that between 1.1 billion and 3.2 billion people will be suffering from water scarcity problems by 2080 and between 200 million and 600 million more people will be going hungry.
The assessment is contained in a draft of a major international report by the UN Intergovernmental Panel on Climate Change (IPCC) to be released later this year, Australia's The Age newspaper said.
Rising sea levels could flood seven million more homes, while Australia's famed Great Barrier Reef, treasured as the world's largest living organism, could be dead within decades, the scientists warn, the newspaper said.
The Age said it had obtained a copy of the report, believed to be one of three prepared for release by the IPCC, which is highly regarded for its neutrality and caution.
Some 500 experts are meeting in Paris this week ahead of the release on Friday of the IPCC's first report since 2001 on the state of scientific knowledge on global warming.
The report will be followed in April by volumes focusing on the impacts of climate change and on the social-economic costs of reducing the emission of greenhouse gases blamed for global warming.
A chapter on Australia in the report on global impacts warns that coral bleaching in the Barrier Reef is likely to become an annual occurrence by as early as 2030 due to warmer, more acidic seas.
Bleaching occurs when the plant-like organisms that make up coral die and leave behind the white limestone skeleton of the reef.
The World Heritage site, stretching over more than 345,000 square kilometers (133,000 sq miles) off Australia's northeast coast, will become "functionally extinct", the scientists are quoted as saying.
Average global temperatures have already risen about 0.7 to 0.8 degrees since 1900, which the report says contributed to increased bleaching in coral reefs in the Caribbean and the Indian Ocean.
At 2.0 to 3.0 degrees above 1900 levels, the report predicts the "complete loss" of Australia's alpine zones and the possible collapse of South America's Amazon forest system, causing a "huge loss of biodiversity".
The human and economic costs of climate change are likely to be highest in poor countries, with water shortages crippling many African nations and increased coastal flooding hitting low-lying countries such as Bangladesh and many Pacific islands, the report says.