The summit, known as Rio+20, was supposed to hammer out aspirational, rather than mandatory sustainable development goals across core areas like food security, water and energy, but the draft text agreed upon by diplomats failed to define those goals or give clear timetables toward setting them.
It is "telling that nobody in that room adopting the text was happy. That's how weak it is," the European Union's climate commissioner Connie Hedegaard said on social network Twitter.
The text "has too much 'take note' and 'reaffirm' and too little 'decide' and 'commit'. (The) big task now for U.N. nations to follow up" on this, she added.
Expectations were low for the summit because politicians' attention is more focused on the euro zone crisis, a presidential election in the United States and turmoil in the Middle East than on the environment.
The first Rio Earth summit in 1992 paved the way for a global treaty on biodiversity, and the 1997 Kyoto Protocol on greenhouse gases, which is due to expire this year. The Rio+20 moniker is a nod to the 1992 summit.
Heads of state and ministers, including Russian President Vladimir Putin, French President Francois Hollande and U.S. Secretary of State Hillary Clinton, will meet with diplomats representing other nations from Wednesday for three days to discuss the text and possibly make some changes to its wording.
Observers do not expect major amendments.
U.S. special envoy for climate change, Todd Stern, told reporters on Tuesday he did not expect the document to change much after heads of state meet to discuss it.
"We don't have anything that we are expecting to try to drive into the document that is not there yet," he said.
'OVER BEFORE IT'S STARTED'
Environmental groups criticized the text, saying it omitted or watered down important proposals and challenged heads of state to act urgently to respond to climate change.
"This summit could be over before it's started. World leaders arriving tonight must start afresh. Rio+20 should be a turning point," said Oxfam spokesman Stephen Hale.
"There's no sign of that here. Almost a billion hungry people deserve better."
The draft text omitted a clause calling for governments to phase out fossil fuel subsidies, which have nearly tripled since 2009, despite a pledge by G20 countries to eliminate them.
Phasing out fossil fuel subsidies by 2020 would reduce annual global energy demand by 5 percent and carbon dioxide emissions by nearly 6 percent, according to the International Energy Agency.
Oil producing countries, including Venezuela and Canada, blocked inclusion of the clause, despite a huge social media push on Monday to include phase-out language in the text, with over 100,000 tweets on Twitter with the hashtag #endfossilfuelsubsidies.
An eagerly awaited decision on a governance structure for the high seas was also postponed for three years, after the United States, Japan, Canada, Russia and Venezuela opposed strong language to implement it.
"There's no commitment - it's like telling your girlfriend you promise to decide in three years whether or not to decide, whether or not to get married," said Susanna Fuller of the High Seas Alliance, a coalition of NGOs.
FOCUS ON IMPLEMENTATION
Others were slightly more optimistic.
"The document represents a positive step forward. While it is not the major breakthrough we had 20 years ago it puts us on the pathway to sustainable development," Selwyn Hart, diplomat for Barbados, told Reuters.
"The formal negotiations might be over but (leaders here tomorrow) need to focus on the implementation of some of the central issues dealt with in the document," he added.
Separately, in a meeting of big-city mayors at an old fortress in Rio, New York City Mayor Michael Bloomberg and colleagues from around the world sought to show how cities, can make progress even if a multi-national agreement isn't possible.
Cities are responsible for up to three-quarters of global greenhouse gases.
Measures already underway in major cities, the mayors said, are on track to reduce their combined emission of greenhouse gases by 248 million tons by 2020, an amount equal to the current annual emissions of Mexico and Canada together.
The measures, the mayors said, include everything from better waste management to more efficient lighting, and would include biofuel and electric-powered municipal transport.
Noting the sluggish pace of the multi-national negotiations, Bloomberg said cities "aren't arguing with each other. We're going out there and making progress."