THE global sustainable development summit that begins this week in Rio is “too important to fail”, the UN secretary general, Ban ki-Moon has said.

In a desperate last-minute plea to world leaders before the meeting, Ban said the international community was in danger of squandering a once-in-a-generation opportunity to use the Rio+20 meeting to map out a new course for economic and social development.

It was the starkest warning from Ban to date that the meeting — being held 20 years after the first Earth summit in Rio which was attended by then US president George H.W. Bush and British Prime Minister John Major — risked failing in its mission of setting out a plan for expanding prosperity and opportunity without destroying the planet’s environment.

“It is too important to fail, too important to fail,” Ban said in an interview at UN headquarters in New York. “We must not waste [this]. We must have a good practical outcome.”

Nobody expected Rio+20 to produce all the answers, Ban said, but it was crucial the leaders at least agree on the bare bones of a plan. “If we really do not take firm actions, we may be heading towards the end — the end of our future,” he warned.

The final round of negotiations leading up to the Rio+20 summit took place recently, amid deepening despair about the prospects of getting world leaders to agree on development goals.

At a lunch with a group of international journalists last month, Ban described the pace of negotiations as “painfully slow”. But with the meeting now only days away, the secretary general tried to put a more positive spin on the plodding path to Rio.

“It’s only natural that when you are dealing with so important, so serious, matters that you have to address these issues until the last minute. It’s not unusual in this type of these mega, big, multilateral conferences,” he said.

Unfortunately for Ban, however, his leadership at the UN is indelibly associated with precisely the kind of diplomatic dysfunction put on display at such mega-conferences.

He spent months elevating the importance of the 2009 climate change conference in Copenhagen, cajoling Barack Obama and other world leaders to attend.

The effort blew up in their faces, when the Copenhagen summit failed to produce a binding climate change treaty. Instead, the meeting exposed the deep divide between rich and poor countries over who should deal with climate change.

Now, some fear, it’s Rio’s turn. After a great deal of build-up, there is little sign that the meeting will heed Ban’s call to put the world on a clear path to sustainable development.

Despite personal appeals, many leaders are staying away from Rio. Barack Obama made it clear recently he would not attend — though he is sending a high-powered delegation led by the secretary of state, Hillary Clinton. David Cameron and Angela Merkel are also giving Rio a miss — the deputy prime minister, Nick Clegg, is leading the UK delegation, along with the environment secretary, Caroline Spelman. —The Guardian, London