Connaughton said China would soon replace the United States -- if it has not already done so -- as the world's largest emitter of greenhouse gases, which trap heat near the Earth's surface and so bring on global warming. He also acknowledged the country's severe air and water pollution.
"I think there are great challenges in China, but I've been encouraged at the innovation at the governmental level in tools for promoting compliance," he said.
Noting that it had taken the United States a generation to implement strong environmental protection policies, Connaughton said: "We did it in less than 30 years. China can do it in less than 30 years, and that's what we look forward to."
Connaughton sidestepped a question on whether China would meet its goal of reducing energy intensity -- the amount of energy that goes into each unit of output -- by 20 percent between 2006 and 2010. Last year, energy intensity fell just 1.33 percent.
"With any of these goals, what matters most is that they are reasonably ambitious, they are technically justified and we have close monitoring to see what is working and what is not working," he said.
Washington has put cooperation on environmental technology at the heart of its top-level "strategic economic dialogue" with Beijing. The two have agreed to develop 15 large-scale coal mine methane capture projects in China in the next five years.
Cooperating on clean coal technology was especially important because 70 percent of the future increase in greenhouse gases will come from coal burnt for power generation, Connaughton said.
During his trip he visited the word's largest coal methane power plant in the northern province of Shanxi, which will use 60 methane-powered generator sets made by Caterpillar Inc.
