China has won international plaudits for its commitment to green goals. It has pledged to reduce carbon emissions by at least 40 percent per economic unit by 2020 and is also adding alternative energy sources such as wind farms and nuclear power plants faster than any other country.

But the nation is also in the midst of unprecedented economic growth--and an unprecedented surge in the use of energy, which for China means coal. The country burns more coal than the U.S., Europe and Japan combined, the main reason why it is now the world’s largest emitter of greenhouse gases. “Will China’s carbon dioxide emissions overwhelm the world?” asks Mark D. Levine, a senior staff scientist at Lawrence Berkeley National Laboratory who works in the country on energy-efficiency measures. “That’s the question.”