LONDON - More than 100 million people will die and global economic growth will be cut by 3.2 percent of gross domestic product (GDP) by 2030 if the world fails to tackle climate change, a report commissioned by 20 governments said on Wednesday.

As global average temperatures rise due to greenhouse gas emissions, the effects on the planet, such as melting ice caps, extreme weather, drought and rising sea levels, will threaten populations and livelihoods, said the report conducted by humanitarian organisation DARA.

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 percent 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 climate-carbon 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 percent of world GDP, or by about $1.2 trillion a year, and losses could double to 3.2 percent of global GDP by 2030 if global temperatures are allowed to rise, surpassing 10 percent before 2100.

It estimated the cost of moving the world to a low-carbon economy at about 0.5 percent of GDP this decade.

Counting the cost

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 told Reuters earlier this year investment equivalent to 2 percent 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 percent.

Temperatures have already risen by about 0.8 degrees Celsius above pre-industrial times. Almost 200 nations agreed in 2010 to limit the global average temperature rise to below 2C (3.6 Fahrenheit) to avoid dangerous impacts from climate change.

But climate scientists have warned that the chance of limiting the rise to below 2C is getting smaller as global greenhouse gas emissions rise due to burning fossil fuels.

The world's poorest nations are the most vulnerable as they face increased risk of drought, water shortages, crop failure, poverty and disease. On average, they could see an 11 percent loss in GDP by 2030 due to climate change, DARA said.

"One degree Celsius rise in temperature is associated with 10 percent productivity loss in farming. For us, it means losing about 4 million metric tonnes of food grain, amounting to about $2.5 billion. That is about 2 percent of our GDP," Bangladesh's Prime Minister Sheikh Hasina said in response to the report.

"Adding up the damages to property and other losses, we are faced with a total loss of about 3-4 percent of GDP."

Even the biggest and most rapidly developing economies will not escape unscathed. The United States and China could see a 2.1 percent reduction in their respective GDPs by 2030, while India could experience a more than 5 percent loss.