Saving the world's poorest people from the effects of runaway climate change will require the West to cut carbon emissions by four-fifths and display the political commitment shown by the US in developing the atomic bomb or putting a man on the moon, the UN said on Tuesday.
In its annual human development report, the UN said the international community would need to invest two-thirds of what is currently spent globally on arms to prevent a buildup in greenhouse gases that would trigger a rise in temperatures of more than 2oC.
The UN said it would cost about 1.6 percent of global GDP -- around US$1.7 trillion a year -- to reduce carbon emissions by 50 percent by 2050, but stressed that a failure to act now would be the 21st-century equivalent of the lack of leadership that led to the 20th century's two world wars.
The report, released in the run-up to next month's UN climate change conference in Bali, said vulnerability to climate disasters was heavily concentrated in poor countries, with 98 percent of those affected between 2000 and 2004 living in the developing world.
One person in 19 living in the world's poorest countries was at risk from climate dangers compared with one in 1,500 in the rich West, the UN said.
Its health check on the state of the world warned that climate change could turn reverse attempts to tackle poverty by reducing food production in areas such as sub-Saharan Africa, exacerbating water shortages in regions such as the Middle East, raising sea levels in low-lying countries such as Bangladesh and Vietnam, damaging fragile ecosystems and damaging human health by increasing the chances of diseases such as malaria.
Rich countries, which account for half of global carbon dioxide emissions but only 15 percent of the world's population, would have to take the lead in preventing the world from using up its carbon budget for the entire 21st century by 2032, the UN said.
"They carry the burden of historic responsibility for the climate change problem. And they have the financial resources and technological capabilities to initiate deep and early cuts in emissions," the UN said.
The UN said that avoiding an increase in global temperature of more than 2oC would require rich countries to cut emissions by at least 80 percent by 2050, with a cut of 30 percent by 2020. Emissions from developing countries would need to peak around 2020, with cuts of 20 percent by 2050.
The scale of the cuts demanded by the UN is far in excess of those currently being considered by policymakers.
The report said reductions of 60 percent in carbon emissions could still leave temperatures rising by 4oC and 5oC and leave carbon levels at between 660 parts per million (ppm) and 750ppm in the atmosphere, way above the 450ppm most experts believe is the Earth's safe limit and which would restrict global warming to 2oC.
That kind of temperature rise, with the related increase in sea levels and disruptive weather, could cause havoc in poorer countries, which would be hardest hit by climate change and which have the least money to mitigate the effects.
The UN said such 80 percent cuts in greenhouse gases would require a range of measures. It called for a global carbon tax to be introduced at a starting rate of between US$10 and US$20 per tonne of carbon dioxide emitted, rising eventually to between US$60 and US$100 a tonne; a beefed-up system of carbon trading; improvements in energy efficiency; extra investment in green technologies; and a global climate change mitigation facility established with a US$25 billion to US$50 billion budget to support low carbon transition in the developing world.