In response to a comment about global warming, I looked up the data for CO2 emissions from the US and China over the last 25 years and made the plots below. The data are from the Energy Information Administration's "Official Energy Statistics from the U.S. Government" on the web here. The data represent emissions of CO2 from the consumption and flaring of fossil fuels. The first plot shows that since 1980, the U.S. has released 2 times as much carbon dioxide as China has. 
Cumulative emissions of CO2, 1980-2004, data source: US Government
The second shows that the contrast is even greater per capita (per person): each year since 1980 the U.S. has released between 4 and 10 times as much CO2 per person as China. 
Per capita emissions of CO2, 1980-2004, data source: US Government
The third plot shows that there is reason to be cocerned about China. Though in recent years the U.S. has continued to emit more CO2 than China, China's emissions are accelerating drastically and will eclipse ours. 
Emissions of CO2, 1980-2004, data source: US Government