Climate change is the biggest global threat to human health this century and will have devastating consequences, from spreading malaria and dengue to food shortages and increased deaths from heatwaves, researchers warn.

A report on managing the health effects of climate change, launched jointly by the Lancet medical journal and University College London (UCL), says global warming will hurt the world's poorest most, even though they have contributed the least to carbon emissions.

"The inequity of climate change - with the rich causing most of the problem and the poor initially suffering most of the consequences - will prove to be a source of historical shame to our generation if nothing is done to address it," warns the study, which is the result of a year's collaboration between the two organisations.

The researchers warn that rising global temperatures will trigger a greater rate of transmission and geographic spread of traditionally tropical diseases like malaria and dengue fever.

And they say more frequent and intense heatwaves will result in higher mortality, as with the 2003 heatwave that caused up to 70,000 deaths in Europe. While some people believe populations in India and Africa may be more resistant to heatwaves, the report says there's little evidence of this and major heatwaves could increase death rates in these populations more than in rich countries.

The security of food and water supplies is also threatened by climate change, with scientists now believing crops are much more sensitive to temperature changes than first thought, the report warns.

"If we are going to get early (climate) changes in the next 20 or 30 years, falling crop yields could trigger more of an effect through rising food prices," said Anthony Costello, the report's lead author and a UCL professor, in a statement.

"Look at what happened last year when food prices rose globally. And one billion people currently have calorie-deficient diets - this situation will get worse as demand increases from India, China and other nations with a population boom."

Water shortages and poor sanitation may also boost malnutrition and gastroenteritis. Up to 250 million people in Africa are expected to face water shortages by 2020 unless action is taken to adapt to climate change.

Estimates show small increases in the risk for climate-sensitive conditions, like diarrhoea and malnutrition, could result in very large increases in the total disease burden, the report warns.

INEQUALITY

A rise in weather-related disasters will hit the populations of poor countries harder than those in wealthy nations, with slum-dwellers and coastal communities particularly exposed to floods and rising sea levels.

At the same time, the fragmented and under-funded health systems of poorer nations will be less able to cope with rising demand triggered by climate change.

"There is massive inequality in health systems throughout the world. Because of this, the loss of healthy life years as a result of global environmental change is predicted to be 500 times higher in Africa than in European nations," said Costello.

The report argues that doctors have stayed silent for too long about the importance of climate change to the future of health and health services, leading to gaps in essential information and research.

It urges health professionals to work with governments, international agencies, NGOs, communities and academics to raise awareness of climate change as an issue that affects human health. They should also do more to promote low-carbon lifestyles, which bring major health benefits by reducing obesity, heart and lung disease, diabetes and stress.

The report also calls for an effort to collate information on the health effects of climate change, leading up to a major international summit in two years' time.

"We especially want representation from poorer nations. This conference would set out some clear indicators, targets, and accountability mechanisms. We need a new 21st-century public health movement to deal with climate change," said Costello.

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