A visitor arriving in Shanghai immediately notices China's technological conundrum. Through the windows of the magnetically levitated train that covers the 30 kilometers from Pudong International Airport to Shanghai at up to 430 kilometers per hour, both the progress the country is making and the price it is paying for it are apparent. Most days, a yellow haze hangs over Shanghai's construction frenzy. Pollution is the leading cause of death in China, killing more than a million people a year. And the primary cause of pollution is also the source of the energy propelling the ultramodern train: coal.

To keep pace with the country's economic growth, ­China's local governments, utilities, and entrepreneurs are building, on average, one coal-fired power plant per week. The power plants emit a steady stream of soot, sulfur dioxide, and other toxic pollutants into the air; they also spew out millions of tons of carbon dioxide. In November, the International Energy Agency projected that China will become the world's largest source of carbon dioxide emissions in 2009, overtaking the United States nearly a decade earlier than previously anticipated. Coal is expected to be responsible for three-quarters of that carbon dioxide.