With world leaders preparing for the three-day Rio+20 meetings beginning tomorrow in Brazil, this is a fitting moment to assess the true legacy of the original Earth Summit of 1992.
In many respects, that meeting was a watershed moment. It brought together a remarkable 172 countries, more than 100 of them represented by their leaders, to start to address at the global level the unsustainable use of natural resources and man's effect on the environment.
Yet, two decades on, all the major scientific indicators continue to flash red. It is now sadly clear that a large part of the Summit's potential has been squandered.
Since 2000 alone, forests equivalent in size to the land mass of Germany have been lost. Today 80 per cent of the world's fish stocks have collapsed or are on the brink of collapse. The Gobi Desert is growing by roughly 10,000 sq km every year.
The list of environmental pressures grows by the day, and there can be little doubt that the unsustainable use of natural resources will be the biggest challenge facing mankind in the 21st century.
So why haven't we done better since 1992? And what needs to be done to correct our course now?
It is not that leaders committed to the wrong objectives in Rio 20 years ago and in Johannesburg in 2002. Those Summits led to the creation of UN conventions on biological diversity, climate change and desertification and the principles on sustainable forestry.
By any standards, these are remarkable achievements that have set in train some key advances such as a significant decrease in deforestation in Brazil and the qualified success of more recent climate summits in Durban and Cancun.
Instead, the major problem has been the failure of governments to implement properly their commitments from Rio and Johannesburg.
First, there has been a lack of domestic legislation to underpin the Rio conclusions. Second, there was a lack of credible, independent international monitoring. Third, the Rio agenda was not translated into the language that holds sway in finance ministries.
If Rio+20 is to be a success, the current generation of world leaders must do better in these areas.
The just-concluded first World Summit of Legislators, bringing together over 300 senior lawmakers, is a big step in this direction, marking the start of a new international process to strengthen delivery of the original Rio agenda, conventions on climate, desertification and biodiversity, and new commitments made at Rio+20.
The World Summit of Legislators had three objectives: to provide a platform to advance laws and share good legislative practice; to establish a global mechanism to monitor the implementation by governments of commitments made in 1992, 2002 and at Rio+20; and finally to incorporate the valuation of natural capital into government accounting.
Perversely, the world still focuses on GDP as the indicator of national wealth, when clearly it does not take into account the stock of natural capital on which all economies rely. A country can expand its GDP, creating the illusion of increased wealth, while becoming poorer by destroying the natural capital on which its long-term prosperity depends.
On Sunday, Summit participants agreed on a Rio+20 legislators' protocol they will take back to their legislatures to seek support or formal ratification. Legislators will then be asked to reconvene every two years to monitor progress in implementing the Rio outcomes, and to share legislative and scrutiny practices.
The World Summit of Legislators was thus just the beginning of a long-term, global process for delivering transformational change that addresses the weaknesses of the original Earth Summit.
If parliamentarians are properly engaged, we are confident we can help create the foundation for genuine sustainable development, and so secure the prosperity of future generations, not just our own.
It is critical that we do so.
Rt Hon John Gummer, Lord Deben, is the former UK Secretary of State for the Environment and president of GLOBE International. Senator Cicero Lucena is 1st Secretary of the Senate of Brazil and president of GLOBE Brazil