Climate change, linked by scientists to human emissions of gases such as carbon dioxide from cars and factories, is causing more frequent floods and droughts and melting ice caps.

"An estimated 150,000 deaths...were caused in the year 2000 due to climate change," the study said. A further 5.5 million healthy years of life were lost worldwide due to debilitating diseases caused by climate change, it said.

"The 1990s were the hottest decade on record and the upward trend in the world's temperature does not look like it is abating," it said. "In Europe this past summer, for example, an estimated 20,000 people died due to extremely hot temperatures."

The situation will worsen if climate trends continue, WHO experts said at a news conference to launch the book.

"We see an approximate doubling in deaths and in the burden in healthy life years lost" by 2030, said WHO scientist Diarmid Campbell-Lendrum.

DIARRHOEA, MALARIA

The book estimated climate change was to blame for 2.4 percent of cases of diarrhoea because, Campbell-Lendrum said, the heat would exacerbate bacterial contamination of food.

Climate change was also behind two percent of all cases of malaria, because increased rainfall created new breeding grounds for mosquitoes which carry the disease, he said.

But he acknowledged global deaths from climate change were minuscule compared with the total number of deaths a year, which the WHO puts at 56 million. About 10 times more people die each year from tobacco-linked illness, he said.

"That doesn't make it more acceptable and the fact is it's likely to get worse," he said. "One of the points about climate change is that people who are affected by it don't have the choice to stop smoking."

While halting global warming was the only long-term cure, immediate actions to fight disease and improve access to health services would also help, Campbell-Lendrum said.

The 180-nation conference in Milan is trying to work out ways to slow climate change, mainly via the United Nations' Kyoto protocol which aims to curb emissions of greenhouse gases.

Not all scientists were convinced by the study, especially by the link it draws between warming and malaria.

"It is naive to predict the effects of 'global warming' on malaria on the mere basis of temperature," Paul Reiter, a professor at Paris's Pasteur Institute, said in a statement.

"Why don't we devote our resources to tackling these diseases directly, instead of spending billions in vain attempts to change the weather?"