The World Summit on Sustainable Development opens here today with a positive spin being put on two days of informal preparatory negotiations on key issues affecting the lives and environments of millions of people throughout the world.
In advance of the arrival this week of ministers and heads of state or government from more than 100 countries, senior United Nations officials were expressing cautious optimism that there would be a positive outcome before the summit ends on September 5th.
An intensive round of negotiations will be necessary to resolve differences over issues ranging from water and sanitation in the world's poorest countries to whether the richer countries are prepared to honour the commitments they made at the first Earth summit in Rio de Janeiro in 1992.
According to Mr Nitin Desai, secretary general of the summit, it must produce "credible commitments" to implement these 10-year-old pledges in line with targets and timetables agreed here.
"Rio focused attention very much on trying to change the way people thought about development," Mr Desai said.
"Here, in Johannesburg, we have to say how we will act. It is about implementation."
And he indicated that globalisation had become one of the sticking points.
According to sources, full agreement has only been reached on four of the 100-plus issues that remain to be resolved at the summit. And even though the atmosphere is described as "positive", it will be a tall order to finalise a credible deal with only 10 days to go.
Tension has already manifested itself in clashes between police and a small group of anti-globalisation demonstrators who protested outside the main police station in central Johannesburg on Saturday. Tear gas and stun grenades were fired to disperse them.
The action taken by the police was defended by the South African Foreign Minister, Ms Nkosazana Dlamini-Zuma, after being challenged at a crowded media briefing by Ms Naomi Klein, author of No Logo, the bible of the anti-globalisation movement.
Ms Klein said the demonstrators were merely taking part in a "candlelight vigil" in protest against the arrest of an American activist, Ms Ann Eveleth, who has been declared a "prohibited person" by the South African authorities and is awaiting deportation.
But the Foreign Minister said that action had to be taken by the police to prevent the Johannesburg summit becoming "a summit of anarchy" - like previous world trade talks in Seattle and Genoa. Some 20,000 police are on duty here to prevent any repetition.
Ms Dlamini-Zuma, a former South African health minister, also noted that "many foreigners" had taken part in a Greenpeace amphibious assault on the country's principal nuclear power plant at Koeberg, near Cape Town, earlier on Saturday. Nine were arrested.
The Earth summit is taking place amid tight security at the opulent Sandton convention centre on the outskirts of Johannesburg. Environment and development activists are holding their own global forum at Nasrec, on the opposite side of the city.
The Minister for the Environment, Mr Cullen, is expected to arrive at the summit tomorrow to take charge of the 30-strong Irish delegation, in advance of the arrival next weekend of the Taoiseach, Mr Ahern, and other European leaders.
The Irish delegation includes representatives of some of the principal environment and development groups which last week denounced Ireland's record on sustainable development; they are already complaining that they have been sidelined in the summit negotiations.
Ms Dlami-Zuma said environment and development activists attending the parallel global forum were quite entitled to demonstrate, but they would have to "obey the law".
She said there was "no anarchy in this country, there is law", and the police had to protect both citizens and property in South Africa from protesters who refused to obey its laws.
The tough line being taken by the South African authorities is obviously designed to deter protesters from engaging in any repetition of the violent scenes that took place at world trade summits in Seattle and Genoa.
On the eve of today's official opening, 14 areas of serious disagreement on central issues remained, like how to bring fresh water, sanitation and energy to the poor; debt relief; overseas aid; the impacts of globalisation, and trade.
There are distinct divisions between the EU, which wants clear targets and timetables for improving the lot of the world's poor, and the US, Japan, Australia and Canada, which are nervous of new commitments.