More negotiations on global "sustainable development goals" ... France's President Francois Hollande will be one of the 120 world leaders at the UN conference.

More negotiations on global "sustainable development goals" ... France's President Francois Hollande will be one of the 120 world leaders at the UN conference. Photo: Reuters

ONCE again 120 world leaders - Julia Gillard among them - are about to attend a United Nations mega conference on the environment with a yawning gap between the dire warnings of ecological devastation and what the politicians appear likely to achieve.

Twenty years after it last hosted the United Nations conference on sustainable development, Rio de Janeiro is again preparing for the arrival of presidents, prime ministers and about 50,000 delegates for the meeting from June 20 to 22.

Unlike the Copenhagen climate change meeting in December 2009, or even the first Rio sustainable development meeting in 1992, this so-called Rio+20 meeting is not aiming for agreement on anything that is legal or binding.

After months of talks even its non-binding ''outcomes document'' remains heavily disputed, with negotiators complaining progress has been agonisingly slow and environment groups such as World Wildlife Fund warning the talks could collapse.

As the negotiations stall, a recent United Nations Environment Program report warned Earth was close to an ecological tipping point, after which '' … abrupt and possibly irreversible changes to the life-support functions of the planet are likely to occur''.

Among the possible ''outcomes'' is an arrangement to start negotiations for a new agreement on global ''sustainable development goals'' - matters such as energy and water use, oceans and food security, with the aim of having them finished by 2015.

The Rio conference agreed on two legally binding conventions, on biodiversity and climate change. The latter is the foundation of the last two decades of international climate talks.