"When I look ahead at Rio and beyond, it seems to me that our scarcest resource is time", says Lester Brown, president at the Earth Policy Institute.
"What we're actually looking at is a race between tipping points, between natural, environmental tipping points on the one hand and political tipping points on the other."
David Suzuki, founder of David Suzuki Foundation, mirrors Brown, calling for urgent action against "the crisis of our time".
"The sense of urgency is absolutely critical. I cannot stand to have just another meeting where people come, do their thing, and then leave as if, oh, back to the same old problems," Suzuki says.
But as Jonathon Porritt, founder of Forum for the Future, argues, the world has been "at a critical point for years" and yet progression in areas such as cutting carbon emissions and scaling up sustainable development is still too slow.
"We know that this critical point is not really a point, it's a sort of period of time that we have available to us to effect these changes and we've been in that available period of time, in my opinion, for at least 20 and I would probably argue 40 years," Porritt says.
Expectations for Rio+20 are generally low but as Bill Ford, executive chairman, Ford Motor Company, believes, the advances in technology and the shift of mindset within some companies, means that the tables have turned since the original Rio conference. More
