Higher temperatures will change rainfall patterns and the length of seasons, and this will have a resounding impact on agriculture and water-borne and insect-borne diseases, it said.

"There is growing evidence that changes in the global climate will have profound effects on the health and wellbeing of citizens in countries throughout the world," Kerstin Leitner, the agency's assistant director-general for sustainable development and healthy environments.

A study launched in Milan by the WHO with the help of three other agencies, garnering the best available scientific data, said that if global temperatures increase by two or three C (3.6-5.4 F), several hundred million more people a year will be exposed to malaria.

"Further, the seasonal duration of malaria would increase in many currently endemic areas," it added.

In 2030, the estimated risk of diarrhoea will be up to 10 percent higher if emissions of carbon dioxide and other "greenhouse" gases that trap the Sun's heat continue to grow unbraked, it said.

As for malnutrition, the study warned of a "significant increase" in India, Bangladesh, Myanmar and Vietnam, which are heavily dependent on having a predictable monsoon for rice growing, but there would be a "small decrease" in China and the other nations of Southeast Asia.

But there are also other, currently unquantifiable risks to health, according to the report.

These include include deaths from heatwaves, of the kind that ravaged Western Europe this summer, the region's hottest on record, and mortality from floods, storms and droughts.

Worsening air pollution and allergens, the emergence of new diseases or old diseases that take a new transmission path, and the advent of novel pests that could blight food crops are other potential factors.

The agencies that worked with the WHO on the study, "Climate Change and Human Health - Risks and Responses," are the UN Environment Programme (UNEP), the World Meteorological Organisation (WMO) and the US Environmental Protection Agency (EPA).

The data basis for it includes the landmark 2001 report by the UN's top scientific body on global warming, the Intergovernmental Panel on Climate Change (IPCC).

The IPCC believes the Earth's average surface temperature increased by about 0.6 C (1.08 F) during the 20th century, of which two-thirds has occurred since 1975, when the effects of the age of oil began to kick in.

It projects a rise of between 1.4 and 5.8 C (2.5-10.4 F) from 1990-2100, with the variation depending on how much action is taken to curb greenhouse-gas emissions.

At the top end of the IPCC's estimates, sea levels could rise by 88 centimetres (55 inches), drowning many small island states and delta regions.

The report was unveiled on the final day of a two-meeting of world environment ministers, attending the December 1-12 gathering of the UN Framework Convention on Climate Change (UNFCCC).

A summary of the document can be downloaded at the WHO website at (http://www.who.int/globalchange).

SPACE.WIRE