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.

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.

If an economy is to sustain progress, it must satisfy the basic principles of ecology. If it does not, it will decline and eventually collapse. There is no middle ground

Yet, most of the readily accessible reserves of oil formed over hundreds of millions of years will be consumed within a single generation, spanning the years from 1960 to 1995.

The foundation is being laid for the emergence of both wind and solar cells as cornerstones of the new energy economy. World wind generating capacity grew from 7,600 megawatts in 1997 to 9,600 in 1998, an expansion of 26 percent. At a national level, Germany led the way, adding 790 megawatts of capacity, followed by Spain with 380 megawatts, and the United States with 226 megawatts. In the past, U.S. wind generating capacity was concentrated in California, but in 1998, wind farms began generating electricity in Minnesota, Oregon, and Wyoming, broadening the new industry's geographical base.

It takes 1,000 tons of water to produce 1 ton of grain. As water becomes scarce and countries are forced to divert irrigation water to cities and industry, they will import more grain. As they do so, water scarcity will be transmitted across national borders via the grain trade. Aquifer depletion is a largely invisible threat, but that does not make it any less real.

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.