Countries disagree about how to pay for cuts to greenhouse gas emissions in poorer nations like India. (Vijay Mathur/Reuters)

Failing to reduce carbon dioxide emissions could cause a global health catastrophe, say doctors in a letter and an editorial in two medical journals.

There is now consensus that carbon dioxide emissions need to be reduced to at most 50 per cent of 1990 levels by 2050 to achieve a 50 per cent chance of preventing temperatures from exceeding preindustrial levels by more than two degrees — often considered the tipping point for irreversible climate change, an editorial in this week's British Medical Journal and the Lancet said.

'What is good for the climate is good for health.'— Dr. Fiona Godlee

"Failure to agree to radical reductions in emissions spells a global health catastrophe, which is why health professionals must put their case forcefully now and after Copenhagen," says the editorial written by Lord Michael Jay, who chairs the health charity Merlin, and Prof. Michael Marmot of University College London.

The next United Nations climate change conference will be held in Copenhagen in December, and a successful outcome at the meeting "is vital for our future as a species and for our civilization," the pair say.

In May, experts warned of the health implications of climate change, such as the spread of mosquitoes carrying malaria and dengue fever to warmer high altitudes, declining crop yields, and more extreme weather like flash flooding that would overwhelm sewage systems.

The editorial argues that people living in poor tropical countries, particularly in sub-Saharan Africa, will suffer more from climate change, and that curbing emissions would also pay off in healthier diets and cleaner air.

In a letter accompanying the editorial, the presidents of 18 medical organizations worldwide, including the Royal College of Physicians and Surgeons of Canada, called on doctors to lobby politicians to act on climate change.

"There is a real danger that politicians will be indecisive," they write. "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."

"[W]e have a responsibility as health professionals to warn people how bad things are likely to get if we don't act now," said Dr. Fiona Godlee, editor in chief of the BMJ. "The good news is that we have a positive message — that what is good for the climate is good for health."

Talks to prepare for the Copenhagen summit have been mired by a lack of agreement on how much to cut emissions and how to persuade poor countries to join the agreement.