One of the world's pre-eminent scientific publications, Nature, has just issued a scathing report card in advance of the Rio+20 summit on sustainable development.

The grades for implementation of the three great treaties signed at the first Rio Earth Summit in 1992 were as follows: Climate Change - F; Biological Diversity - F; and Combating Desertification - F. Can humanity still avoid getting itself expelled?

We have known for at least a generation that the world needs a course correction.

Instead of powering the world economy with fossil fuels, we need to mobilize much greater use of low-carbon alternatives such as wind, solar, and geothermal power.

Instead of hunting, fishing, and clearing land without regard for the impact on other species, we need to pace our agricultural production, fishing, and logging in line with the environment's carrying capacity.

Instead of leaving the world's most vulnerable people without access to family planning, education, and basic healthcare, we need to end extreme poverty and reduce the soaring fertility rates that persist in the poorest parts of the world.

In short, we need to recognize that with seven billion people today, and nine billion by mid-century, all inter-connected in a high-tech, energy-intensive global economy, our collective capacity to destroy the planet's life-support systems is unprecedented. Yet the consequences of our individual actions are typically so far removed from our daily awareness that we can go right over the cliff without even knowing it.

When we power our computers and lights, we are unaware of the carbon emissions that result. When we eat our meals, we are unaware of the deforestation that has resulted from unsustainable farming. And when billions of our actions combine to create famines and floods halfway around the world, afflicting the poorest people in drought-prone Mali and Kenya, few of us are even dimly aware of the dangerous snares of global interconnectedness.

Twenty years ago, the world tried to address these realities through treaties and international law.

The agreements that emerged in 1992 at the first Rio summit were good ones: thoughtful, far-sighted, public-spirited, and focused on global priorities. Yet they have not saved us. Those treaties lived in the shadow of our daily politics, imaginations, and media cycles. Diplomats trudged off to conferences year after year to implement them, but the main results were neglect, delay, and bickering over legalities. Twenty years on, we have only three failing grades to show for our efforts.

Is there a different way? The path through international law engages lawyers and diplomats, but not the engineers, scientists, and community leaders on the front lines of sustainable development. It is littered with technical arcana about monitoring, binding obligations, annex-I and non-annex-I countries, and thousands of other legalisms, but has failed to give humanity the language to discuss our own survival.

We have thousands of documents but a failure to speak plainly to one other. Do we want to save ourselves and our children? Why didn't we say so? At Rio+20 we will have to say so, clearly, decisively, and in a way that leads to problem-solving and action, not to bickering and defensiveness.

Since politicians follow public opinion rather than lead it, it must be the public itself that demands its own survival, not elected officials who are somehow supposed to save us despite ourselves. There are few heroes in politics; waiting for the politicians would be to wait too long. The most important outcome in Rio, therefore, will not be a new treaty, binding clause, or political commitment. It will be a global call to action.

Around the world, the cry is rising to put sustainable development at the center of global thinking and action, especially to help young people to solve the triple-bottom-line challenge - economic well-being, environmental sustainability, and social inclusion - that will define their era. Rio+20 can help them to do it. Rather than a new treaty, let us adopt at Rio+20 a set of Sustainable Development Goals, or SDGs, that will inspire a generation to act.

Opening the eyes

Just as the Millennium Development Goals opened our eyes to extreme poverty and promoted unprecedented global action to fight AIDS, tuberculosis, and malaria, the SDGs can open the eyes of today's youth to climate change, biodiversity loss, and the disasters of desertification. We can still make good on the three Rio treaties, by putting people at the forefront of the effort.

SDGs to end extreme poverty; decarbonize the energy system; slow population growth; promote sustainable food supplies; protect the oceans, forests, and drylands; and redress the inequalities of our time can galvanize a generation's worth of problem-solving. Engineers and technology wizards from Silicon Valley to Sao Paolo to Bangalore to Shanghai have world-saving ideas up their sleeves.

Universities around the world are home to legions of students and faculty intent on solving practical problems in their communities and countries. Businesses, at least the good ones, know that they can't flourish and motivate their workers and consumers unless they are part of the solution.

The world is poised to act. Rio+20 can help to unleash a generation of action. There is still time, just barely, to turn the F's to A's, and to pass humanity's ultimate test.

The author is professor of economics and director of the Earth Institute at Columbia University. Copyright: Project Syndicate, 2012.www.project-syndicate.org