"I'm not going to stand here and pretend what is in that text is going to make some indelible mark on the world's history from tomorrow on.
"But I do think it is putting the spotlight on sustainable development ... and oceans."
Gillard, the first Australian Prime Minister to visit Brazil, was praised by UN Secretary-General Ban Ki Moon as he appointed her to co-chair, with Rwanda, of a body that will make the final push towards meeting the MDGs.
"I really count on the Prime Minister's strong visionary leadership and commitment," Ban said.
A week before the carbon tax starts, he said Australia was "leading by example" in addressing climate change.
The MDG group, which also includes British rock star Bob Geldof, will rally nations to do more to end poverty, provide clean water, food and education and boost foreign aid.
Australia has delayed meeting its target for a year to deliver a budget surplus in 2012/13.
Gillard's climate efforts were also praised by South Korean President Lee Myung Bak, who welcomed Australia joining the Global Green Growth Institute and putting A$15 million ($19.1 million) towards fostering ties between the private sector, academia and government to pursue model projects.
South Korea is also introducing an emissions trading scheme.
Gillard earlier launched a global network - initially involving Australia, Brazil, Norway and New Zealand - to bring together Australian Aboriginal people with other indigenous peoples of the world to share knowledge on managing land and sea.
About 56 heads of state and 31 heads of government are set to sign a 50-page non-binding document tackling poverty, sustainable development and environmental protection.
Australian Greens senator Larissa Waters, who is attending the summit, said she was disappointed Gillard was taking a "defeatist" approach and not making further changes to the document put together by diplomats.
"Frankly these are the people we have elected to speak for us - it should be their call," she said.
Contentious issues such as technology transfers from rich to poor nations and new financing for developing countries were set aside in the draft document. Diplomats agreed on what all call a mere beginning, a step towards a roadmap on how to embrace sustainable development at the three-day conference.
"The future we want has [got] a little further away today. Rio+20 has turned into an epic failure. It has failed on equity, failed on ecology and failed on economy," said Kumi Naidoo, executive director of Greenpeace. "This is not a foundation on which to grow economies or pull people out of poverty, it's the last will and testament of a destructive 20th century development model."
Ban acknowledged the world had made little progress on environmental issues since the first Rio meeting in 1992, but said leaders were working to reverse that.
"Twenty years ago, the Earth Summit put sustainable development on the global agenda. Yet let me be frank: our efforts have not lived up to the measure of the challenge," he told delegates. "For too long, we have behaved as though we could indefinitely burn and consume our way to prosperity. Today, we recognise that we can no longer do so.
"We recognise that the old model for economic development and social advancement is broken. Rio+20 has given us a unique chance to set it right," Ban said.
French President Francois Hollande said he wasn't too excited about the summit's likely results.
"Disappointment, yes, there's always a bit of disappointment. But I've come here to show my hope, my confidence."
- AAP, AP
