The world will face a global health catastrophe if governments fail to agree deep cuts in greenhouse gas emissions as part of a U.N. pact in Copenhagen in December, several leading doctors have declared.

What's good for the climate is good for health, according to an editorial published in the British Medical Journal and The Lancet on Wednesday.

A strong agreement in Copenhagen by 190 nations to curb emissions would help avert heatwaves, floods and desertification that would disrupt water supplies and cause malnutrition and disease, especially in poor nations.

Failure to agree radical reductions in emissions spells a global health catastrophe, wrote authors Michael Jay, chair of the Merlin medical relief charity, and Michael Marmot, director of the International Institute for Society and Health.

The measures needed to combat climate change coincide with those needed to ensure a healthier population and reduce the burden on health services. A low carbon economy will mean less pollution, their editorial said.

A low-carbon diet (especially eating less meat) and more exercise will mean less cancer, obesity, diabetes, and heart disease. Opportunity, surely, not cost, they wrote.

NONE SPARED

Separately, a group of presidents of colleges of physicians and medical academies in nations including the United States, Australia, Hong Kong, Canada, Thailand, Britain and Nigeria urged doctors to demand more action from governments.

They also said impacts on health could be catastrophic and noted in a letter to the two medical journals that a report in May concluded that climate change was the biggest health threat of the 21st century.

While the poorest in the world will be the first affected, none will be spared, they wrote. Doctors are still seen as respected and independent, largely trusted by their patients and the societies in which they practice. As leaders of physicians across many countries, we call on doctors to demand that their politicians listen to the clear facts that have been identified in relation to climate change and act now, they wrote.

More than 190 nations will meet in Copenhagen from December 7-18 to agree a broader successor to the U.N.'s Kyoto Protocol, which obliges developed nations to cut

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