It calculated that five million deaths occur each year from air pollution, hunger and disease as a result of climate change and carbon-intensive economies , and that toll would likely rise to six million a year by 2030 if current patterns of fossil fuel use continue.

More than 90% of those deaths will occur in developing countries, said the report that calculated the human and economic impact of climate change on 184 countries in 2010 and 2030.

It was commissioned by the Climate Vulnerable Forum, a partnership of 20 developing countries threatened by climate change. "A combined climatecarbon crisis is estimated to claim 100 million lives between now and the end of the next decade ," the report said.

It said the effects of climate change had lowered global output by 1.6% of world GDP, or by about $1.2 trillion a year, and losses could double to 3.2%of global GDP by 2030 if global temperatures are allowed to rise, surpassing 10 % before 2100.

It estimated the cost of moving the world to a low-carbon economy at about 0.5% of GDP this decade. Responding to the report , Oxfam International said the costs of political inaction on climate were "staggering" .

"The losses to agriculture and fisheries alone could amount to more than $500 billion per year by 2030, heavily focussed in the poorest countries where millions depend on these sectors to make a living," said executive director Jeremy Hobbs.

British economist Nicholas Stern said earlier this year investment equivalent to 2% of global GDP was needed to limit, prevent and adapt to climate change. His report on the economics of climate change in 2006 said that without any action to tackle climate change, the overall costs and risks of climate change would be equivalent to a cut in per-capita consumption of perhaps up to 20%.