They said the gathering had let down millions of people and organisations who had been inspired by he original 1992 Earth Summit to change their outlook and their lives. It had also further strained relations between rich and poor countries.
The meeting ended with developed nations insisting that they would not make any unambiguous, timetabled commitment to end the decline in their overseas aid to poor countries. It was a commitment Britain was willing to make, but the United States, Japan, Canada, Germany and France would not.
Overseas aid has been falling since the 1992 summit, even though all developed countries apart from the US promised back then that it would rise. But now they stress that developing nations will have to rely increasingly on private sector money for development, either from within their own economies or from overseas.
The developed countries as a whole would not commit themselves to any figure for reducing emissions of climate changing, greenhouse gases, although they are obliged to do so at a climate treaty meeting later this year.
There was no agreement in New York on the need for an international forest convention. Nor do the European Union's proposals for an international tax on aviation fuel - one of the fastest-growing sources of greenhouse gas emissions - make any real progress.
Tony Juniper, campaigns director of Friend of the Earth UK, said: "We came here knowing not to expect too much, but it has been a dismal failure.
"The atmosphere here has shown that the world community cannot agree on the vision needed to save the world, and that's frightening. Nations are deeply entrenched behind their own interests."
Andrew Simms, of Christian Aid, said "negotiations have failed to not lived up to expectations because there's been no trust between the developed and developing countries. The issue is economic justice and it has not been addressed here."
Merylyn McKenzie Hedger, climate campaigner with the World Wide Fund for Nature, said: "There was no way it was ever going to be a great success, but now it's a question of how big a failure this has been. We're calling it Rio Minus 5."
However, Michael Meacher, Britain's Minister for the Environment who has been negotiating on the final text late into the night, refused to be pessimistic. He said: "A new world order is gradually and painfully coming into play, but with enormous resistance from the old pattern of forces."
He also praised President Bill Clinton's speech, in which he said the US had to take the threat of global warming seriously, but failed to give any clue about how much it would cut its emissions by.
Summits are largely talking shops, but even their sternest critics would agree that they get the press and leading politicians thinking about and discussing environmental issues. Summits spawn other talking shops, and some of the talk eventually does lead to concrete actions which shift economies towards sustainable development.
The crunch on global warming will come at United Nations Climate Treaty talks in Kyoto in Japan in December when developed nations have promised to make commitments to cut their greenhouse gas emissions after 2000.