Last week's summit has confirmed that sustainable development will only be achieved through the political leadership of developing countries.
Two and a half years ago, the Copenhagen climate change conference (COP15) ended in rancorous and highly public disagreement between developed and developing nations on what was needed to prevent further global warming.
The outcome proved an intense embarrassment to the host nation, Denmark.
From the beginning of negotiations over the UN Conference on Sustainable Development (dubbed Rio+20), which took place in Rio de Janeiro, Brazil, last week, it was widely reported that the Brazilian government was desperate to avoid the same fate.
Although Brazil's determination was only one contributory factor, the result was the agreement, by all 188 participating nations, on an outcome document that was filled with aspirations and exhortations about the need for the world to move to a more sustainable path of economic and social development, but lacking any firm commitment to the more painful steps needed to achieve this goal.
Inevitably, this outcome has satisfied virtually no-one engaged in the process (apart from the host country).
But the increased focus that it provided on the political realities on which the Copenhagen meeting foundered — and which Rio+20 ducked — has itself been a significant step forward.
Taking the lead
What became clearer than ever at Rio was that the key to global sustainable development does not lie in the logical arguments coming from proponents in the developed world, including its scientific communities, however passionately they are delivered.
Rather, it now lies in the combination of political muscle and imaginative thinking in the developing world, particularly the so-called 'emerging economies' of countries such as Brazil, China and India.
In Rio, these countries insisted, quite legitimately, that a global commitment to making the transition to 'green economies' is only valid if it includes a transfer of significant financial and technical resources from the North to the South.
Their argument was that such a transfer would compensate for the fact that this transition is necessary because of the consumption patterns of the North.
Furthermore, the emerging economies — and China in particular — are coming to realise that sustainable development is in their own interest.
At the same time, a combination of technical ingenuity and low labour costs makes them well placed to become the leading producers of sustainable technologies for the rest of the world — as China has already shown in exporting solar energy technologies to Africa, for example.
Galvanising the grassroots
The organisers of Rio+20 were keen to emphasise that even as the formal proceedings turned out to be disappointing, this had been partially compensated for by the enormous networking opportunities the meeting provided for sustainable development stakeholders.
In particular, by the end of the meeting, more than 700 pledges — valued at over US$500 billion — had been registered for concrete actions through, for example, individual institutional commitments or partnership agreements.
Each of these was required to commit to quantifiable outcomes within a fixed timeframe. Together they show that a massive global commitment to sustainable development already exists, even without promises of resource transfers from political leaders.
Indeed, this outcome appears to confirm what many have been arguing: that truly sustainable economies can only be built from the grassroots, and with the full inclusion of community groups and other interested stakeholders.
Reigning in corporate power
But even if grassroots or voluntary initiatives are a necessary condition for sustainable development, they are not sufficient.
In particular, it ignores the extent to which the key directions and components of economic growth — such as a continued reliance on non-renewable energy sources supported by generous subsidies — are inevitably set at the top, rather than the bottom, of the political pyramid.
Furthermore, without an all-embracing political framework to ensure coherence between individual actions, each stakeholder remains — equally inevitably — motivated primarily by their own self-interest (or that of their stakeholders or shareholders), rather than a commitment to a common good.
For example, many of the 700 individual pledges registered at Rio involved individual commitments from corporations keen to be seen to be 'going green'.
Ironically, however, former Norwegian Prime Minister Gro Harlem Brundlandt, head of the Brundlandt Commission, which first coined the phrase 'sustainable development' in the 1980s, accused corporate lobbyists of being partly responsible for the disappointing outcome of the formal negotiations. 
Paving the future
The scientific meetings held in the run-up to Rio+20 — including both the Planet Under Pressure meeting in London in April, and the International Council for Science and UN Educational, Scientific and Cultural Organization's Forum on Science, Technology and Innovation for Sustainable Development, held two weeks ago in Rio itself — both underlined the urgency of taking action on many fronts.
Rio+20 opened the door for action on some of these, such as protecting the marine environment or mountain ecosystems. It also endorsed closer interaction between scientific communities and policymakers — another essential element of any future strategy.
But the meeting also highlighted the political challenge of changing the course of a global economy still wedded largely to fossil fuels and non-sustainable patterns of consumption.
It also showed that the developed world lacks the commitment to make the necessary changes and accept the painful consequences, pursuing the familiar maxim that 'turkeys don't vote for Christmas'.
It is now up to the developing world and its emerging economies to show that they can do better — for example, by taking on a key role in defining the forthcoming Sustainable Development Goals — and providing the political muscle to make this happen.
Concerns about embarrassment over possible failure should not stop them from taking the necessary political risks.