The World Health Organisation (WHO) has estimated that climate change leads to more than 150,000 deaths every year and at least 5 million cases of illness.

In a review of the impact of global warming on public health, researchers at the University of Wisconsin-Madison and the WHO predict countries in Africa and coastal nations along the Pacific and Indian Oceans will be hardest hit.

"Those most at risk from global warming are also those least responsible for causing the problem. There is a real ethical message from the paper," said Jonathan Patz of the UW-Madison's Nelson Institute for Environmental Studies.

"Global warming is not only an environmental problem but a serious health threat," he added in an interview.

Greenhouse gases are expected to increase global average temperature by about 6 degrees Fahrenheit by the end of the century, causing extreme flooding, more droughts and intense heatwaves.

The researchers said model-based forecasts suggest the risk of climate-related disease assessed by the WHO will more than double by 2030. Flooding will affect the lives of up to 200 million people by the 2080s and heat-related deaths in California will more than double by 2100.

"Many of the most important diseases in poor countries, from malaria to diarrhoea and malnutrition are highly sensitive to climate," said Diarmid Campbell-Lendrum, of the WHO, and a co-author of the report published in the science journal Nature.

DISAPPEARING GLACIERS

In addition to increasing health problems, warmer temperatures will reduce glaciers and snow packs which could disrupt water supplies in some regions of the world.

More water will fall as rain, rather than snow, so reservoirs will fill earlier than normal. Water shortages could result in areas where reservoirs and dam capacities are insufficient, according to a separate review in the journal.

"Mother nature is not going to act like a reservoir as it has in the past and when the water comes out all at once, there isn't enough capacity to contain it," said Tim Barnett, of the Scripps Institution of Oceanography at the University of California, San Diego.

Along with scientists at the University of Washington, Barnett said vanishing glaciers will have the most impact on water supplies in the future in China, India and other parts of Asia, which has the third largest ice mass in mountainous areas on Earth.

In South America, many people living west of the Andes mountains will also be at risk of shrinking water supplies.

"Climate warming is a certainty for our future and ... the long-term prognosis is clear and very dire," Barnett said in a statement.