More than 100 world leaders, but not America's Barack Obama or Britain's David Cameron, gathered in Rio de Janeiro yesterday for a three-day UN summit on sustainable development – the formula for bringing millions of people out of poverty without trashing the environment.

The gathering at "Rio Plus 20" marks the 20th anniversary of the so-called "Earth Summit" in Rio in June 1992, regarded as one of the most influential environmental gatherings ever, not least for the two UN treaties it saw signed on climate change and biodiversity.

Expectations this time are much lower and have been steadily dropping all week, especially since the draft final text, entitled "The Future We Want", was released two nights ago. Many environmental and developmental groups say it contains no new commitments for anyone to do anything, no targets and no timetables, and it is unlikely to be strengthened when heads of state and government agree to it tomorrow.

"This summit was over before it even started," Oxfam's Antonio Hill said last night. "World leaders failed to seize the day. This summit will be recognised as a failure – a fail on equity, a fail on ecology and a fail on economy. We always knew government ambitions were low, but the final deal lacks a single new meaningful commitment."

The sense that the conference might not make decisions of substance clearly influenced Mr Obama and Mr Cameron's decisions to stay away. The President has sent Hillary Clinton, his Secretary of State, in his place, and Mr Cameron has sent the Deputy Prime Minister, Nick Clegg. German Chancellor Angela Merkel is another prominent rich-country absentee.

But all the leaders of the "Brics" group of leading developing countries – Brazil, Russia, India, China and South Africa – are present, as the issue of development is something they cannot afford to ignore. The summit's significance may depend on pronouncements today and tomorrow from the likes of Russia's Vladimir Putin, China's Wen Jiabao or India's Manmohan Singh.

Yesterday the summit was opened by UN Secretary-General Ban Ki-Moon, who admitted the draft outcome was disappointing. "Some member states hoped for a bolder, ambitious document," he said. "But you should understand that negotiations have been very difficult and very slow because of all these conflicting interests."

* Leading British companies will be made to report their greenhouse gas emissions from the beginning of the next financial year, Nick Clegg announced in Rio yesterday. The new rules will apply to London Stock Exchange-listed businesses from April 2013 to allow investors to see which companies are managing their pollution effectively, and the scheme could be rolled out to all large companies from 2016.

A global challenge: Rio's key players

Brazil

206m Population (World rank: 5)

1.1% Population growth rate (Rank: 102)

2.7% Economic growth rate (Rank: 133)

Key environmental issues: Ongoing efforts to reduce deforestation in the Amazon, the world's largest rainforest, but eradicating logging altogether would be financially disastrous.

China

1.34bn Population: (Rank: 1)

0.5% Population growth (Rank: 152)

9.2% Economic growth rate(Rank: 7)

Key environmental issues: The biggest emitter of CO2, with 24 per cent of the world total. A recent report claimed only 1 per cent of city dwellers breathe air deemed safe by the EU. Unparalleled pollution problem.

India

1.21bn Population: (Rank: 2)

1.3% Population growth(Rank: 88)

7.8% Economic growth rate: (Rank: 15)

Key environmental issues: Third behind China and the US in CO2 emissions. Lacks forceful legislation on the environment. Its "lawless" mining industry has been criticised. Air and water quality remain a huge problem.

Russia

138m Population (Rank: 9)

-0.48% Population growth (Rank: 219)

4.3% Economic growth rate(Rank: 91)

Key environmental issues: Currently eyeing delicately balanced Arctic ecosystems as potential sources of exports of oil and gas. Government accused of wielding country's vast natural reserves as a political tool. Water pollution and air quality have still not recovered from lack of industrial regulations in Soviet era.

South Africa

48.8m Population(Rank: 26)

-0.41% Population growth (Rank: 217)

3.4% Growth rate(Rank: 119)