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."