The UN sustainable development summit in Rio de Janeiro has formally opened with a warning from UN head Ban Ki-moon that progress on the issue is too slow.
The secretary-general told world leaders and other ministers that "words must translate into action".
On the summit's fringes, international finance institutions launched a $175bn fund to boost sustainable transport.
And the UK government announced that major businesses will have to report their carbon emissions from next year.
Mr Ban opened the session with a reference to the historic Earth Summit held here in Rio 20 years ago, which spawned UN conventions on climate change, biodiversity and desertification, as well as the Agenda 21 blueprint for sustainable development.
"Since then, progress has been too slow - we have not gone far enough down the road," he said.
"We are now in sight of a historic agreement - the world is waiting to see if words will translate into action, as we know they must."
Mr Ban's comments suggested that there were still decisions for the estimated 130 heads of state and government, and ministers from other countries, to take here.
However, there has been no indication that any are planning to re-open talks on the agreement that their negotiators concluded on Tuesday, before the high-level talks began.
The opening session also heard from 17-year-old New Zealander Brittany Trilford, who won a competition organised by climate change campaign group tcktcktck to send a message behalf of the world's youth.
Referring to the remaining length of the summit here, she told world leaders: "You have 72 hours to decide the fate of your children - my children - my childrens' children - and I start the clock now.
"Are you here to save face - or are you here to save us?"
The meeting has seen a slew of announcements from financial institutions and business groups on stimulating green development.
Perhaps the most significant came from a group of eight international development banks led by the Asian Development Bank, who are preparing to pump $175bn into sustainable transport schemes over the next decade.
Greenhouse gas emissions from transport are growing faster than from any other economic sector.
The banks calculate that air pollution, congestion, traffic accidents and climate impacts can take 5-10% off a country´s GDP per year.
"This is a game changer for sustainable transport," commented Holger Dalkmann, of the World Resources Institute's center for sustainable transport.
"It will ensure that hundreds of millions of people will have cleaner air, less congested roads, and safer transportation.¨
UK Deputy Prime Minister Nick Clegg used the Rio+20 platform to announce that from next year, companies listed on the main market of the London Stock Exchange will have to report their greenhouse gas emissions annually.
Green groups have been pushing for such a commitment for years, believing it will stimulate concerned consumers, investors and the companies themselves to curb emissions.
"Counting your business costs while hiding your greenhouse gas emissions is a false economy," said Mr Clegg.
"British companies need to reduce their harmful emissions for the benefit of the planet, but many back our plans because being energy efficient makes good business sense too."
Alan McGill, a sustainability partner with consultants PwC, said the move should not come as a surprise to businesses.
"Regulations on emissions reporting will indirectly increase everyone's attention on the issue," he said.
"The reputational risks and impacts of people sharing information quickly and globally cannot be underestimated."
The remainder of the week will see a sequence of set-piece speeches by heads of national delegations, who in most cases - though not in the UK's - are heads of state or heads of government.
However, there is already a palpable feeling in the corridors that the serious business is over.
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