The Rio+20 summit next year should focus on reshaping the world economy to better "manage the planet," the UN's top environment official told AFP at climate talks in Durban.

"Rio will help the world look at climate change in the broader context of the changes we need to bring about in our global economy," United Nations Environment Programme (UNEP) Executive Secretary Achim Steiner told AFP on the sidelines of the 12-day negotiations, which end Friday.

"We are moving toward a world of nine billion people that will face food and climate insecurity, economic shock, unemployment."

The June 20-22 event in Rio de Janeiro is taking place 20 years after the landmark 1992 Earth Summit that set down UN conventions for protecting biodiversity and tackling global warming.

Steiner called on leaders to rethink the way they define economic growth because, he said, the current approach is straining the planet's coping capacity to the breaking point.

"We need a new indicator of wealth. GDP growth is too crude, even misleading," Steiner said in an interview.

"It served us well as long as the world was full of resources. But the world has reached the point where it has to optimise the way it manages the planet."

One way to visualise the problem is this: beginning in the 1970s, humankind demanded more than the planet could provide.

Earth's seven billion denizens, in other words, are using more water, cutting down more forests and eating more fish than Nature can replace.

At the same time, we are disgorging more CO2, pollutants and chemical fertilisers than the atmosphere, soil and oceans can soak up without crippling the ecosystems upon which we depend.

"Rio+20 is about the future of our economies, but not in the narrow sense," Steiner said. "It must address this question: how sustainable will our societies be if we do not address these issues more clearly?"

But better management of the planet does not mean redressing Earth's growing imbalances through brute re-engineering, he added.

Faced with deepening impacts from global warming and chronic deadlock in UN climate talks, attention is turning to a raft of untested technological fixes ranging from seeding the atmosphere with radiation-repelling particles to sowing the ocean with iron.

"People are advocating experimenting with our planet with very inadequate knowledge," said Steiner.

"Learn how Nature has developed carbon capture and sequestration capacity, in forests, soils, and sea marshes. Why try and second guess nature? These are proven methods."

The conference, recently rescheduled to avoid a scheduling clash with Queen Elizabeth II's diamond jubilee to ensure that world leaders could come, will also consider an upgrade for UNEP.

As a UN "programme," it does not have an guaranteed budget but depends on voluntary contributions from member nations. Gaining the same status as the World Health Organisation (WHO), for example, would considerably increase it clout.

"We are in desperate need of a more effective system for international envirornmental governance," said Steiner.

More than 120 nations have requested that boosting UNEP's status be put on the Rio+20 agenda, he said.