BANGKOK (Reuters) - Humans must make sweeping cuts in greenhouse gas emissions in the next 50 years to keep global warming in check, but it need cost only a tiny fraction of world economic output, a major U.N. report said on Friday.
The Intergovernmental Panel on Climate Change (IPCC) said keeping the temperature rise within 2 degrees Celsius (3.6 F) would cost only 0.12 percent of annual gross domestic product.
"It's a low premium to pay to reduce the risk of major climate damage," Bill Hare, a Greenpeace adviser who co-authored the report told Reuters after marathon talks that ran over their four-day schedule to finalize the document.
The report "shows that it's economically and technically feasible to make deep emission reductions sufficient to limit warming to 2 degrees," he said.
To keep within that limit, which scientists and the European Union say is needed to stave off disastrous climate changes, carbon dioxide emissions need to fall 50 to 85 percent by 2050, said the report, the third in a series.
However, technological advances, particularly in more efficient energy use and production, meant such targets were within reach, it said.
It stressed the use of nuclear, solar and wind power, more energy-efficient buildings and lighting, as well as capturing and storing carbon dioxide spewed from coal-fired power stations and oil and gas rigs.
But A U.S. environmental official rejected some options detailed in the report for cutting emissions as too costly.
"There are measures that come currently at an extremely high cost because of the lack of available technology," said James Connaughton, head of the White House Council on Environmental Quality.
These scenarios, he said, would bring cuts in world gross domestic product of up to 3 percent. "That would of course cause global recession, so that is something that we probably want to avoid," Connaughton said in a telephone briefing.
China, expected to soon overtake the United States as the world's biggest greenhouse gas producer, said rich countries must not keep clean energy technologies to themselves.
"It is something the developing countries have been asking for many years, but up till now it has not happened," said Zhou Dadi, director of China's Energy Research Institute and a co-author of the report.
The panel also said for the first time that lifestyle changes could help fight global warming.
It gave no examples, but IPCC chairman Rajendra Pachauri said these could include turning down the thermostat and eating less red meat, which could cut animal methane emissions.
The report, agreed by scientists and officials from more than 100 countries, reviews the latest science on the costs and ways to curb emissions growth. It is meant as a blueprint for governments without telling them exactly what to do.
Its clear message, however, was that the ball was now in government courts. "There is no excuse for waiting," European Environment Commissioner Stavros Dimas said.
U.N. Secretary-General Ban Ki-moon said a "comprehensive package on the way forward" needed to be launched at a December U.N. climate change conference in Bali, Indonesia, so there was no gap when the Kyoto Protocol's first phase runs out in 2012.
In some cases, the IPCC said, technology could bring major benefits, such as cutting health costs by tackling pollution.
Even changing planting times for rice or managing livestock herds better could cut emissions of methane, said the report, which draws on the work of 2,500 scientists.
Two previous IPCC reports this year painted a grim future of human-induced global warming causing more hunger, droughts, heat waves and rising sea levels that would drown low-lying islands.
Asia's population is most at risk from rising seas and more powerful storms. One in 10 people, mainly in Asia, live in highly vulnerable coastal areas, an international study published last month found.
The steeper the emissions cuts, the greater the cost to the global economy, the report said.
The cost of limiting greenhouse gases in 2030 to stabilization levels of between 445 and 710 parts per million (ppm) CO2-equivalent ranges from a 3 percent decrease in global GDP to a small increase, it said.
However, regional costs might differ significantly from global averages, it added. Greenhouse gas concentrations are now at about 430 ppm CO2-equivalent.
Additional reporting by Darren Schuettler in Bangkok, Deborah Zabarenko in Washington and Patrick Worsnip at the U.N.