* U.N. urges "decoupling" of raw material use and GDP growth
* Says resource use could triple by 2050 to 140 bln tonnes
* China called a test case for global economy
By Alister Doyle, Environment Correspondent
OSLO, May 12 (Reuters) - The world must curb soaring use of resources ranging from coal to copper to prevent consumption from reaching ruinous levels by 2050, according to a U.N. report on Thursday that says China's economy will be a test case.
All countries should seek economic growth that does not rely on increasing exploitation of minerals, ores, fossil fuels and biomass -- such as timber -- as poverty declines and the world population rises, it said.
Resource use totals about 47 to 59 billion tonnes a year -- according to the study which lumps everything together by weight from oil and gold ore to sand or cement used in construction. Without restrictions, that could leap to 140 billion by 2050.
"Decoupling makes sense on all the economic, social and environmental dials," Achim Steiner, head of the United Nations Environment Programme (UNEP) which produced the 174-page report, said in a statement.
"Decoupling is not about stopping growth. It's about doing more with less. Global resource consumption is exploding. It's not a trend that is in any way sustainable," added Ernst von Weizsacker, co-chair of the UNEP resource panel.
"China is, in many ways, the test case for the global economy," the report said of the most populous nation with 1.3 billion citizens of almost 7 billion worldwide. Beijing in 2007 set a goal of becoming an "ecological civilisation".
Each of the world's citizens consumes about eight to 10 tonnes per year of the materials on average, with people in rich nations using double the average and those in poor African nations far less. China's use is around average.
China "wants to continue its rapid economic growth but use resources more sustainably," the report said. Beijing's steps to reconcile those goals "will be of crucial significance for every other developing country with similar policy intentions".
The study said decoupling was already under way, but needed to accelerate. World gross domestic product grew by a factor of 23 in the 20th century, resource use rose by a factor of eight.
"There is a need for policy changes. The market alone won't do it," Marina Fischer-Kowalski, a lead author of the report at the Alpen-Adria University in Austria, told Reuters.
"It's a common challenge to reach a different kind of growth," Mark Swilling, the other lead author at the University of Stellenbosch in South Africa, told Reuters.
Some cheap and high-quality sources of materials such as oil, copper and gold were already running low. Extraction from lower-grade deposits was already adding strains by requiring ever more use of fossil fuels and fresh water.
A steady shift to living in cities might help -- people in urban areas generally consume less than those in rural areas.
Steiner said the level of resources used by each person "may need to fall to between 5 and 6 tonnes" by 2050. Even so, the study acknowledged that seemed too restrictive as a global goal.
Per capita consumption of the key resources in countries including the United States, Canada and Australia were now well above 20 tonnes. A less drastic scenario would mean all nations aiming for around 8 tonnes per capita by 2050, still demanding deep cuts by rich nations.
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Editing by Elizabeth Fullerton