The outcome of the Rio+20 summit provides further proof that the nation-state system is failing badly in tackling global environmental threats, say analysts.

The UN's Conference on Sustainable Development had been billed as a once-in-a-generation chance to overhaul an economic model that had left a billion people in poverty and imperiled the biosphere.

But veteran observers who watched the 10-day event drag to a close on Friday shook their heads in dismay.

To them, it was a fresh failure by the United Nations system, after the near-disastrous 2009 Copenhagen climate summit, to respond to eco-perils that are now approaching at express speed.

"It's a demonstration of political impotence, of system paralysis, and it makes me feel pessimistic about the system's ability to deliver," Laurence Tubiana, director of a French think-tank, the Institute for Sustainable Development and International Relations (IDDRI), said in an interview.

"The multilateral process today is not delivering the urgent action we need," WWF's Jim Leape told AFP in an email.

"International action is in fact important, to galvanize a global response to these challenges, but it's clear that we need to look to leadership in other places... that means looking for changes everywhere -- communities, cities, national governments and companies."

After a three-day summit of 189 nation-states, the conference issued a 53-page declaration with the horizon-sweeping title "The Future We Want."

It itemized a distressingly long list of problems -- from global warming, deforestation and fisheries collapse to water stress, pollution and biodiversity loss that scientists fear could turn into a mass extinction.

But long months of textual trench warfare, as nations defended their own interests, meant radical proposals were either watered down or got the chop.

They included a commitment to phase out subsidies for fossil fuels and demands for up to $30 billion a year to help poor countries grow in a sustainable way.

Connie Hedegaard, the European commissioner for climate change, admitted that "to the normal citizen, it (the outcome) doesn't sound a lot."

Even so, Europe had cemented references to the green economy, which set an important precedent, "something to build on in the years to come," she said.

Observers said the most tangible success was a plan for "Sustainable Development Goals" to succeed the UN's Millennium Development Goals, which touch on health, poverty and so on, after they expire in 2015.

In an interview with AFP carried on its Geopolitics blog (http://blogs.afp.com/geopolitics), Jeffrey Sachs, director of the Earth Institute at Columbia University in New York, said the MDGs had been an important catalyzer -- but for ordinary citizens, not leaders.

"They have been a global call to action that has mobilized millions of people around the world, as well as informed, nudged or pushed governments to take seriously the challenges of poverty, hunger and disease.

"They thus teach us a lesson: we cannot rely on the politicians and the diplomats to get this job done."

After Copenhagen, some critics said the UN system was genetically incapable of coping with a global environment crisis.

Solutions demand sacrifice by all nations, which gives any dissenter the chance to sabotage or weaken a radical deal.

But Steve Sawyer, a former Greenpeace campaigner who is now secretary general of a Brussels clean-energy lobby, the Global Wind Energy Council, said the UN still offered hope.

"The UN system has lost its way," crippled by the format determined by the victors of World War II, he argued.

"For all its warts, it's what we have, and there is no alternative," he said.

"To deal with global problems, we need a global framework, and to make that work we need the big powers to drive it and not fight against it. So we're hoping that the Chinas, Indias, Brazils, Germanys and Japans will take up some of the slack."