Failure to tackle climate change at a key UN conference in Copenhagen could be "catastrophic" for health, the heads of 18 doctors' associations warned on Wednesday.
In an exceptional joint appeal published in the British Medical Journal (BMJ) and The Lancet, they called on governments to act decisively to roll back the threat from global warming.
Scientists have repeatedly warned climate change could affect health in many ways, ranging from malnutrition caused by drought to the risk of cholera from flooding and the spread of mosquito-borne disease to temperate zones.
"Doctors must take a lead in speaking out," said the doctors' letter.
"There is a real danger that politicians will be indecisive, especially in such turbulent economic times as these.
"Should their response be weak, the results for international health could be catastrophic."
The December 7-18 meeting under the UN Framework Convention on Climate Change (UNFCCC) aims to set down action for tackling heat-trapping carbon emissions beyond 2012, when the current provisions of the Kyoto Protocol run out.
The letter was signed by the presidents of 18 colleges of physicians or academies of medicine from the United States, Australia, Britain, Canada, Ireland, Thailand, Hong Kong, Malaysia, Ireland, South Africa and Scotland.