As world leaders prepare for the Rio+20 meeting in just over a week, now is a fitting moment to assess the true legacy of the original Earth Summit in 1992.
In many respects, the summit was a watershed moment for the environment. It brought together a remarkable 172 countries, more than 100 of which were represented by their leaders, to start to address at the global level the unsustainable use of natural resources and man's impact on the environment.
Yet, two decades on, all the major scientific indicators continue to flash red. And, sadly, it is now clear that a large part of the summit's original potential has been squandered.
Since 2000 alone, forests equivalent in size to the landmass of Germany have been lost; 80% of the world's fish stocks have collapsed or are on the brink of collapse; and the Gobi desert is growing by roughly 10,000 square kilometres 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 achieve a course correction now?
Crucially, it is not that leaders committed to the wrong objectives at Rio 20 years ago and in Johannesburg 10 years later. These summits led to the creation of the UN conventions on biological diversity, climate change and desertification, the principles on sustainable forestry and Agenda 21.
By any standards, these are remarkable achievements that have set in train some key advances. Examples include the significant decrease in deforestation seen in Brazil, and the qualified success of the recent climate summits in Durban and Cancun.
Instead, the major problem in the past 20 years has been the failure of Governments to implement properly their commitments from Rio and Johannesburg. Three particular parts of the jigsaw puzzle have been missing since 1992.
First, there has been a lack of domestic legislation to underpin the Rio principles and conventions. Second, there was a lack of credible and independent international scrutiny to monitor delivery. And finally, the international community failed to convert the original Rio agenda into a language that would hold sway in the most powerful departments in each government: the treasuries and finance ministries.
These are three critical omissions and, if Rio+20 is to be a success, they must be addressed by the current generation of world leaders.
We are delighted that the Brazilian government, the Mayor of Rio and the UN Secretary-General have recognised this. And that is why The Global Legislators' Organisation (GLOBE), supported by the UN, will convene the first World Summit of Legislators of more than 300 key legistlators immediately before the Rio+20 meeting of world leaders.
It has three objectives. First, it will provide a platform to advance laws and share good legislative practice to underpin the Rio commitments. Second, it will establish a mechanism at the international level to monitor the implementation by governments of commitments made at the original Rio Earth Summit, Johannesburg and Rio+20.
The third objective is about incorporating the valuation of natural capital into government accounting. Perversely, we still focus on GDP as the indicator of national wealth, when clearly it is only a partial measure of income that does not take into account the stock of natural capital on which we all depend and our economies rely.
A country can expand its GDP, creating the illusion of increased wealth, while becoming "poorer" as it destroys the natural capital on which its long-term prosperity depends. Recognising the role of many national parliaments in approving budgets and national accounts, the World Summit of Legislators will examine how the value of natural capital can be integrated into our national economic frameworks.
The summit participants will agree a Rio+20 legislators' protocol. Legislators will be asked to commit to take the protocol 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, as well as to share good legislative and scrutiny practices.
If parliamentarians are properly engaged, we are confident we can help create the foundation for genuine sustainable development, and secure the prosperity of future generations, not just our own.
• Senator Cicero Lucena is first Secretary of the Brazilian senate and President of GLOBE Brazil. Lord Gummer is a former UK environment minister and president of GLOBE International.
Article originally appeared in The Guardian.