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 have warned in a leaked report.
A draft of the report, obtained by Australia's The Age newspaper, estimates that a lack of water will affect between 1.1 billion and 3.2 billion people.
The report says that between 200 million and 600 million more people will go hungry by the same date.
The assessment is contained in a document to be published by the UN's intergovernmental panel on climate change (IPCC), to be released later this year.
Homes threatened
The newspaper says that scientists warn that rising sea levels could flood seven million homes, while Australia's Great Barrier Reef, the world's largest living organism, could be dead within decades.
The report is believed to be one of three prepared for release by the IPCC.
About 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 impact of climate change and on the social-economic costs of reducing the emission of greenhouse gases blamed for global warming.
Reef worries
A chapter on Australia in the report is said to warn 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.
Average global temperatures have already risen about 0.7C to 0.8C since 1900, which the report says contributed to increased bleaching in coral reefs in the Caribbean and the Indian Ocean.
At 2C to 3C 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.
The report says the human and economic costs of climate change are likely to be highest in poor countries.
Water shortages are likely to cripple many African nations and increased coastal flooding will hit low-lying countries such as Bangladesh and many Pacific islands.