The road from the airport ran through miles of open fields when delegates arrived in Rio de Janeiro for the original Earth Summit in 1992.
Twenty years on, with Brazil's population up by 50 million, that same highway runs through a sprawling conurbation of high-rise flats, some measure of the increased toll humankind is exacting from our planet.
A lot of high-flown rhetoric ushered in last week's UN Conference on Sustainable Development. Rio+20 was the biggest summit the UN had ever organised. Some 40,000 environmentalists and 10,000 government officials gathered with politicians from 190 nations for a meeting which the UN Secretary-General Ban Ki-moon said was "too important to fail".
But fail it did. It ended on Friday with an unambitious, non-binding statement which made few advances on what was agreed 20 years ago. Activists such as Greenpeace International called it "an epic failure". Technocrats such as Maurice Strong, who ran the 1992 summit, called it a "weak" collection of "pious generalities". Politicians such as Nick Clegg called it "insipid". No wonder in Brazil protesters ritually ripped up the final text and renamed the summit "Rio minus 20".
Perhaps it was naive to expect better. All the signs had pointed to a lack of political will for real change. Over the past two decades, only four of the world's 90 most important green goals had seen significant progress. We've repaired ozone levels, removed lead from petrol and provided clean drinking water in the world's urban areas. But there has been little done on food shortages, ocean pollution, fish stocks or desertification. We have been wiping out species and destroying rainforests at an unprecedented rate. Our planet is getting hotter; greenhouse gas emissions have risen by 48 per cent so that they are now not far off the level that scientists fear will trigger irreversible climate changes.
The problem is this: the agreements at the 1992 summit were based on a compact in which poor countries said they would green their economies if the rich countries paid for it. Poor nations would create jobs without creating more of the belching coal-fired smokestacks with which the rich nations had got the planet to such a precarious position in the first place.
But the simple polarity of rich and poor nations no longer applies. Some developing countries have become emerging economies. Countries such as China now want to clean up their environments and change their development models on their own terms. And while really poor nations still need foreign aid to adopt green technologies, rich countries aren't feeling rich enough now to stump up the required $30bn a year to fund the transition to sustainability.
Barack Obama, Angela Merkel and David Cameron did not even bother to turn up in Rio. They knew that the summit's final agreement would be big on woolly feel-good phrases and utterly denuded of the dates and measurable targets to make it meaningful. Only seven of the agreement's 287 paragraphs begin "We commit". By contrast, the feeble "We encourage" features 50 times. Governments couldn't even agree a way of stopping their $1trn- a-year subsidy for fossil fuels.
Yet for all that, Rio+20 was not a total waste of time. The signposts to a greener future were to be found not in the conference hall but in more than 3,000 fringe events. Many of these were innovators focused on small-scale technology solutions. Others were private companies, big and small, that see sustainable development not as some corporate social responsibility PR stunt but as integral to enhancing their productivity and competitiveness.
The head of Unilever was there lobbying for a common set of sustainability goals. The insurance giant Aviva was pushing for it to be made mandatory for companies to report on their green activities. Asda, Philips and PepsiCo backed compulsory publication of carbon emissions. A new generation of business leaders is connecting company success with social and environmental issues that were previously the concern only of NGOs.
Business people and activists have been presented with an important new task by Rio+20. Two developing countries, Guatemala and Colombia, came up with a new idea – a set of new sustainable development goals (SDGs) as successors to the millennium development goals which expire in 2015. The Millennium Development Goals aimed to halve world poverty with specific targets on education, health and child mortality. They will not be fully achieved by 2015 but they have proved very useful yardsticks.
The underwhelming Rio+20 agreement did agree to proceed towards SDGs but avoided any attempt to define them. The challenge for eco-activists now is to do that in a way which creates specific mechanisms for the transition to a greener world economy. Universally accepted SDGs were one of the things the head of Unilever, Paul Polman, was lobbying for in Rio.
Politicians have a history of being followers rather than leaders in such matters. They had to be dragged by Jubilee 2000 activists to forgiveness of unpayable Third World debt. It was ordinary people, through Make Poverty History, who forced them into the great leap forward in aid that came at Gleneagles. We may now need a similar bottom-up mass movement of individuals to get real progress on saving the planet.