Prince Charles said he had "watched in despair" at the slow pace of progress on the "critical issues of the day," in a pre-recorded video address in Rio.
He urged world leaders to adopt a more integrated approach to issues such as climate change and food security.
Waiting for the worst to happen would be "too late to act at all", he said.
Rio+20, the United Nations Conference on Sustainable Development, is attended by heads of state and representatives from governments, non-governmental organisations and the private sector.
In his address, the prince said scientific evidence showed the potential consequences of ignoring the risks.
'Sceptical reluctance'
"Like a sleepwalker, we seem unable to wake up to the fact that so many of the catastrophic consequences of carrying on with 'business-as-usual' are bearing down on us faster than we think, already dragging many millions more people into poverty and dangerously weakening global food, water and energy security for the future," he said.
It is, perhaps, a trait of human nature to act only when the worst happens, but that is not a trait we can afford to rely on here”
"One thing is clear. We need to be much more informed about the actual state of the planet. More
