Today, more than ever, we need political leaders who can see the big picture, who understand the relationship between the economy and its environmental support systems.

Our numbers expand, but Earth's natural systems do not.

The challenge is either to build an economy that is sustainable or to stay with our unsustainable economy until it declines. It is not a goal that can be compromised. One way or another, the choice will be made by our generation, but it will affect life on earth for all generations to come.

Saving Greenland is both a metaphor and a precondition for saving civilization. If its ice sheet melts, sea levels will rise 23 feet. Hundreds of coastal cities will be abandoned. The rice growing river deltas of Asia will be under water. There will be hundreds of millions of rising-sea refuges. The word that comes to mind is chaos. If we cannot mobilize to save the Greenland ice sheet; we probably cannot save civilization as we know it.

In Mexico City, Tehran, Kolkata, Bangkok, Shanghai, and hundreds of other cities, the air is no longer safe to breathe. In some cities, the air is so polluted that breathing is equivalent to smoking two packs of cigarettes per day.

We can build an economy that does not destroy its natural support systems, a global community where the basic needs of all the Earth's people are satisfied, and a world that will allow us to think of ourselves as civilized. This is entirely doable.

In this era of tightening world food supplies, the ability to grow food is fast becoming a new form of geopolitical leverage, and countries are scrambling to secure their own parochial interests at the expense of the common good.