FOR DECADES, many believed that nuclear war represented the only apocalyptic threat to human civilization. Today, we know better. We know that any number of environmental or human catastrophes pose grave risks. These are not just problems for individual nations. These are the problems of an interdependent world, and so they are our problems.

These threats may take decades to develop, and they respect no borders. They can be solved only through coordinated and cooperative global efforts. And America must lead, because it's the right thing to do and because our national security is at stake. We must act now: if we wait 10 or 20 or 50 years to confront these challenges, it will already be too late.

We need a Marshall Plan for the 21st Century that partners developed nations, the U.N., non-profit organizations, and the private sector in a massive, multilateral effort. We will assist the developing world in stimulating economic opportunity, protecting the environment, combating pandemics, and conserving water supplies.

A central part of this initiative must be to take immediate and bold steps toward creating a clean energy future. The foundation for this future will be my comprehensive energy plan, which the Sierra Club has called the most aggressive of any candidate for President.

From improving automobile efficiency to 50miles per gallon to instituting a nationwide cap-and-trade system to reduce carbon emissions by 80 percent, my plan offers a realistic and aggressive approach to creating energy and environmental security.

Environmental degradation takes many forms, but the most urgent is global warming. There is an overwhelming scientific consensus that the planet is getting hotter. Three hundred million human beings live less than 15 feet above sea level. Unless we act now, homes, villages, cities, and entire nations will be submerged under rising waters caused by melting ice caps.

Those not displaced by these rising waters may go hungry, as our unrestrained addiction to fossil fuels threatens both regional and global food supplies. Already, severe drought has cut the world's wheat supplies to near their lowest level in 26 years.

More than one billion people depend on fish as their main source of protein, but today less than one-quarter of world fish stocks are healthy. Droughts caused by climate change could leave up to 1.5billion people without enough water to survive.

We must act to arrest and reverse global warming, and we must act now.

We must also remember that more than a billion people survive on less than one dollar per day, and nearly half of the world's two billion children live in poverty. At the same time, infectious diseases -- which strike hardest at those who have the fewest resources to fight back -- are growing more resistant to treatment. They are spreading with a vengeance, and Americans are not immune.

A second plank, then, of my plan to combat these global threats requires leading the world against global poverty. As a nation, we must have the resolve to honor our U.N. Millennium goal commitments, and we must have the audacity to demand that others meet theirs. When I am President, we will double our annual foreign assistance. Furthermore, the World Bank will not be a place for politics. Its only ideology will be the relief of suffering.

We must also focus on education in developing nations. One hundred and fifteen million of the world's children – sixty percent of them girls -- do not receive any schooling at all. In too many countries, a virtual apartheid exists, in which women are frozen out of the workforce and civic life.

Unleashing the economic power of women through education can be the silver bullet that makes every problem easier to fight.

Finally, we must fight cross-border crime. Sophisticated criminal networks running black market trade in arms, drugs and human beings threaten the security of us all. Financial assistance to developing nations should be tied to swift and solid progress toward the eradication of human trafficking. We must end slavery forever.

These are serious challenges, and now is not the time for political calculation. We cannot afford another President who believes that stubbornness is strength. We cannot afford more leadership that has not been tested. To triumph over these challenges, we need to act courageously and compassionately, with an abiding faith in the founding principles of our nation: equality, freedom and human dignity.

Bill Richardson, governor of New Mexico, is running for the Democratic nomination for President.