An article in the NYT on China's plans to create a market for trading permits to emit greenhouse gases told readers that China has the world's second-largest economy after the United States. According to the International Monetary Fund's estimates, China's economy is currently more than 20 percent larger than the U.S. economy, using a purchasing power parity measure. This measure, which applies a common set of prices to the goods and services produced in both countries, is clearly the correct measure of output to use in an analysis of greenhouse gas emissions.
The piece also wrongly asserts that:
"Chinese emissions per person are still somewhat less than the average per capita figure in the United States, although the gap has been narrowing."
While it is true that the gap in per person emissions has been narrowing, the U.S. still emits more than twice as much per person as China.